[aprssig] UHF/VHF Voice Alert (rev 1)

Robert Bruninga bruninga at usna.edu
Fri Jul 31 20:53:27 CDT 2009


For your UHF/VHF Cross Band regional APRS Voice Alert System.

You recall last month or so, I announced our local plans to put
up a 445.925 RECEIVER cross-banded to a 144.39 T100 Voice
Transmitter on a major mountain top so that APRS mobiles could
call Voice Alert over the entire central part of the state.  It
was one-way only, of course, because if the return path was
implemented, then the UHF output would be wall-to-wall T100
packets.  The caller simply announced "WB4APR cross-band Voice
Alert, listening on the 147.xx repeater"...  It was a one-way
call. 

But there is a better way... Make the return path be listening
on 146.52 T100!

Here is the cross band repeater plan:

445.925 input PL 100 goes to 144.39 PL 100 output.
146.52  input PL 100 goes to 445.925 PL 100 output

This way, any APRS operator needing to do an emergency call-up
of ALL APRS mobiles within central Maryland can put out a call
on 445.925 and get relayed to EVERY APRS mobile running Voice
alert (listening wit CTCSS 100 on 144.39).

The standard call is "WB4APR crossband Voice Alert, listening
146.52 PL 100"

This arrangement gives the same long-range call-back capability
as the outgoing call.

Again, once any QSO is established, they move to an agreed
mutual voice repeater.

This unique arrangement solves the problem of just using 144.39
backwards.  Remember, EVERY APRS mobile with voice alert has his
packets going out with PL 100 on them.  SO if we just let the 2m
radio listen on 144.39 with PL 100, all we would hear on the
445.925 would be packets 24/7.  But using 52 T100, we only hear
people intentionally calling us back.  

It is so frustrating to have all those APRS mobiles out there,
and have a "situation come up" and not be able to call-up all
mobiles in range.  Again, even people with dumb trackers, can
still monitor Voice Alert and join this system.

Bob, Wb4APR





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