[aprssig] D700 Tip. Reading Mail

Robert Bruninga bruninga at usna.edu
Tue Jul 31 14:52:09 EDT 2007

>>> How do we call CQ locally on APRS?
>>Voice Alert.  Each of packet contains a 100 HZ tone which will
>>be heard [by] all surrounding APRS also running Voice Alert.
> I never quite got this.   In order for this to work, 
> I'd need to run PL squelch, right?  So how, then, 
> would my APRS station be able to hear, say, the 
> local digi or WX station that *isn't* transmitting 
> a PL of 100?  

The D7 and D700 take their TNC data from the radio receiver in
front of the CTCSS tone squelch.  The CTCSS tone squelch only
silences the speaker in the D7 and D700.  This is why we can get
dual use from the 144.39 APRS channel for both APRS data
(without PL) and for the occasional human-to-human voice call
with PL 100.

Running Voice Alert in the mobile, is like adding another free
radio channel in the APRS mobile.  This hidden-back-channel is
for being able to make a voice call to such an operator on a
guaranteed known voice calling channel that you know he is
monitoring... Because you hear his (and only his) packet when he
is in SIMPLEX range (about 1 to 3 miles)...

It works!

But the WORST killer of this function is HOME stations or 24/7
parked cars that still TX their Voice Alert PL100 packets
*without* an operator present.  This is very frustrating since
other voice alert mobiles that might be passing by, hear these
"CQ's" yet no one is listening in response.  

So remember, Voice Alert is a MOBILE-to-mobile system only.
Home stations that TX it continuously can kill the golden goose
due to QRM.  People willturn their APRS channel volume down and
forget about it, and then they also do not hear voice calls to

Of course you CAN monitor with CTCSS 100 from home for passing
simplex mobiles BUT ONLY IF YOU DO NOT TX PL100 24/7.  Problem
is that most radios cannot independently set their RX CTCSS
without also automatically enabling their TX PL...  This is why
we simply ask home stations to never TX with voice alert


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