Is there a method to limit the people with access to a simplex channel? I would like to utilize a channel that is set up for just myself and my wife. If I gave directions to meet somewhere I would only want her to know where and when we would meet.
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$\begingroup$ Consider Cell Phone SMS to a "Drop Box". Wife can retrieve, delete, and answer. Don't share your "Drop Box" with anyone else. Anyone inadvertently accessing the "Drop Box" message, would have no information as to who it was from / to or what it references, unless your text gives that away. $\endgroup$– OptionpartyCommented Mar 3, 2017 at 17:24
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1$\begingroup$ Martin, welcome to ham.stackexchange.com. Please consider taking the tour to get the most from the site. $\endgroup$– rclocher3Commented Mar 3, 2017 at 21:16
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$\begingroup$ Adding the 'legal' tag without mentioning a country is extremely unhelpful. I know people tend to assume the USA, but that is by no means always the case $\endgroup$– Scott Earle ♦Commented Mar 9, 2017 at 1:40
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$\begingroup$ friendly reminder: please accept an answer or clarify what is not satisfactory about the answers you've gotten. This site stops working if askers don't give feedback!! $\endgroup$– Marcus MüllerCommented Apr 15, 2017 at 10:25
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4 Answers
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There is a way to use radio waves to hold a private conversation.
It's called a mobile telephone, and they are available with surprisingly good coverage around the world.
We should always use a tool appropriate for the task at hand. Amateur radio is not suitable for the use case you are describing, and a mobile phone is.
answered Mar 9, 2017 at 1:42
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$\begingroup$ Private from your neighbor, maybe. Not necessarily private from from your telephone provider, government, and anyone who does business with them. $\endgroup$– Chris_FCommented Jan 3, 2021 at 22:08
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$\begingroup$ @Chris_F if you desire, you can lay end-to-end encryption over a phone line with something like the Signal app. $\endgroup$– webmarcCommented Jul 30, 2023 at 17:13
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You cannot limit others from using a channel.
But as long as you have a license then you can operate anywhere in the band in question, and there are a lot of underutilized frequencies.
Just be sure to ID at the start of your transmission and every 10 minutes if it goes on longer than that.
Privacy is relative, though. Someone with a scanner might catch your transmissions. You can use CTCSS to open her squelch just for you, but that won't hide you from scanners. So in that sense there is no legal way to have a truly private channel.
If she has a license she can answer. But without a license she would be in violation to even just click the PTT button to acknowledge reception of your transmission.
You might want to consider the FRS (Family Radio Service) units where both of you can talk all you want. The better ones also can use CTCSS so neither of you need to listen to whatever other chatter may be on the same channel.
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1$\begingroup$ (At least in ZA) Amateur radio is only for communication between licensed stations, so one-way transmission like this isn't technically allowed. Your wife would also need a license. However we all make experimental one-way transmissions, tuning up, testing, etc, and those would be in the spirit. Funny, on some repeaters 20 years ago, I would hear ham couples saying "I'm on my way home now" and "thanks, see you soon". $\endgroup$– tomnexusCommented Aug 21, 2021 at 15:52
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No. It is not legal. You may not hide the content of your message when making use of amateur frequencies, no matter what means you use to do so.
Technically, all you would need is radios supporting a digital voice mode that includes encryption, but I can't name one that would definitely work simplex (e.g. P25 can be encrypted but is as far as I know always “trunked”, requiring a repeater).
If you wish to pursue this then you would need to use non-amateur frequencies, e.g. by purchasing a ‘business band’ license (details vary by jurisdiction; that's the USA concept). At this point you have to compare the cost with other methods of communication.
answered Mar 2, 2017 at 18:43
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$\begingroup$ P25 can operate in conventional (i.e. not trunked mode). There are ham repeaters that use P25. They are not trunked. And, as far as I can tell from online information, P25 can also work simplex. Not sure about phase 2 TDMA though. $\endgroup$– WA9ZZZCommented Aug 22, 2021 at 1:57
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$\begingroup$ D-STAR works fine in simplex mode. $\endgroup$ Commented Aug 23, 2021 at 19:58
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This topic came up in a discussion on a Facebook ham page.
I had my own thoughts on legally narrowing the available listeners when setting up my mobile to cross-band repeat so as to catch it with my HT:
- Use a non-open-source digital mode. Yaesu’s C4FM-based System Fusion is a good example. It is registered with the FCC, but for all intents and purposes, you can only transmit and receive by using one of their digital radios.
- Use an off-the-beaten-path simplex frequency. For example, I set my cross band output to 147.520. It is not a standard “channelized” 2m simplex frequency in the USA, but available.
- Use tone-squelch (tx AND rx) and do so with one of the more obscure tones: like 177.3Hz
- Yaesu also has the “DG-ID” (one for tx, and another for rx) intended for establishing and simplifying local group communications. Say, code TX to 21 and rx to 89. Works similar to CTCSS, but isn’t— they are just digital codes.
- Finally, it was just suggested to me by another Yaesu user, to use Yaesu’s “VW” (digital Voice Wide) mode. Almost no one uses it, and is somewhat counter-intuitive to digital modes in that it uses the full available bandwidth in sending only voice data. The idea is to have the highest quality digital voice sound, but like I said, it is rarely employed.
Combining all those legal schemes, at once, would make it highly unlikely anyone else will be eavesdropping—even if they were intent on trying.
— KI5KWG, Crews
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1$\begingroup$ Be aware that using any significant power for a "non-open source" mode would be considered to be concealing the communication, which is illegal in the US. Additionally, using tone squelching will prevent you from hearing others, but will do nothing to prevent others from hearing your conversation. The DG-ID approach sounds good, but is again not private since others can choose to listen in. Combining some of those might help to make listening less likely, but some of what you've listed won't really help at all. :) :) $\endgroup$– David Hoelzer ♦Commented Aug 21, 2021 at 11:30
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1$\begingroup$ Hello Crews, and welcome to this site! :-) $\endgroup$ Commented Aug 21, 2021 at 20:35
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2$\begingroup$ I would go on to suggest that even more "off the beaten path" than a 2m simplex frequency would be the entire 220MHz band. $\endgroup$– DustonCommented Aug 23, 2021 at 13:36