[aprssig] APRS Voice Alert

A.J. Farmer (AJ3U) farmer.aj at gmail.com
Thu Sep 8 18:43:14 CDT 2005

On 9/8/05, Steve Huston <huston at astro.princeton.edu> wrote:
>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.

You don't need a TNC to "hear" the packet.  This is just a PL/CTCSS
function, it has nothing to do with a TNC.  All you need is your
receiver tuned to 144.39 with a CTCSS of 100.  All of the transmitters
that are transmitting normally without a PL of 100 will be muted by
your receiver so your your receiver will be silent the majority of the
time.  The only time you will hear packet bursts is if a transmitter
is within simplex range and is transmitting with a PL of 100.

As I stated in an earlier post, I have a non-APRS radio in my wife's
car and I keep 144.39 with CTCSS of 100 in the scan list.  This is
just so I can hear any voice alert packets.  It is silent the majority
of the time.  The radio pauses for a second when there is activity on
the channel, but the speaker is muted and it quickly resumes the scan
when it does not detect a the PL tone.  There is no TNC involved at

Hope that helps!

A.J. Farmer, AJ3U

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