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.
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.
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.
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.
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