[aprssig] Re: APRS Voice Alert

Stephen H. Smith wa8lmf2 at aol.com
Thu Sep 8 18:48:50 CDT 2005

> Steering more towards the topic at hand, does anyone know of good  
> radios that can be modded in such a way that you could still do voice  
> alert?  As an example, I thought of looking for a commercial radio  
> (like an older Motorola or Midland) that I could retune to 390.  But,  
> the second trick would be to tie the TNC in so that it acts like a  
> D700, where the TNC hears the packets but only spits out a data burst  
> through the speaker if the 100Hz PL tone is there.

Nothing special needs to be done.  Just operate PL encode/decode 
normally as you would on a voice channel.  The only requirement is to 
connect the TNC audio-in (receive) line to a source of RX audio 
somewhere before the squelched stage of the radio's receiver.  

On any Moto or other commercial land-mobile rig,  there are test points, 
used for alignment test sets, connected directly to the receiver 
discriminator that are the perfect point to grab an RX signal unaffected 
by the carrier or tone squelch systems.   Many of the newer radios 
actually  have such connectors on the rear panel for attaching tone 
signalling options or mobile data modems. 

If nothing else, one can grab a signal off one of the pins of the 
internal socket for  the optional plug-in CTCSS (a.k.a. "PL") module, 
since the the PL detector HAS to be able to continuously hear the 
discriminator audio in order to decode it and unmute the speaker. 

Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com

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