[aprssig] FRS radios and PTT

Steve Noskowicz noskosteve at yahoo.com
Mon Mar 14 14:47:28 EDT 2011

--- Stephen H. Smith wrote:
> Huh?   What does this mean? What two voices?

The 4.5 kHz is detected in the VOX circuit just like a voice signal is.  Therefore it is another "voice" hense Bob's caps VOICE instead of quotes.

  You should indicate why you want to just key the radio without voice...?

  While this is very clever and I like it, for anyone else trying this, some advice.

Obviously these have the VOX before the low pass filtering in the audio path.  Other radios may not. (this will also "work" on Ham HTs and other radios.

1 - Use the lowest amplitude of tone to reliably operate the VOX.
2 - You'll need to do some investigation on the frequency so you use the highest frequency that triggers the VOX, yet it can't make it through the sudio path and into the modulation.
3 - #2 and #1 are in conflict with each other. Higher frequencies will be atenuated more by he audio filtering, but it may take a higher level to trigger the VOX.
4 - Remember that once you truly talk, you don't need the tone.  This tone and your audio are additive and could clip in the audio chain creating distorion of the voice.

 73, Steve, 


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