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Robert Bruninga wrote:
<blockquote cite="mid:23D9269B92E44FD7ADD3EE2479A7C94E@ewlab.usna.edu" type="cite">
<pre wrap="">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.
</pre>
</blockquote>
<br>
No it doesn't ! Assuming anyone actually responds to this incredibly
confusing kludge, they transmit back to you on '52, but you hear them
but miss their response. Now when you transmit "Please repeat that" on
UHF, it goes out on 144.390, not on '52. So they miss your response
since they have dialed their 2M rig off of 144.39 (unless they have TWO
2-meter radios, or a D700-type "dual-dual-bander"; i.e. capable of
having both sides on different frequencies in the SAME band.)<br>
<br>
<br>
Further, you will have an acute "hidden transmitter" problem on '52.
'52 is relatively heavily occupied and fairly active. <br>
<br>
1) The mobile APRS user hears your call on '39. <br>
<br>
2) He quickly fumbles around and selects '52 with PL transmit.<br>
<br>
3) Being a low-level station (i.e. mobile) he CAN'T hear the activity
on '52 over a large area that your cross-band repeat site can, so he
keys up. <br>
<br>
4) Assuming he is lucky and arrives at your mountain top stronger
than other activity elsewhere on '52 to successfully and positively
capture the '52 RX, the PL tone on his transmitted signal now
unsquelches the mountain top '52 RX.<br>
<br>
5) While his PL tone holds the RX squelch open, other NON-PL'ed
signals on '52 will also get picked up by the RX, resulting in a
howling mess of non-capture heterodynes retransmitted on the UHF
downlink. <br>
<br>
[This is not hypothetical -- it happens all the time here in the west
with cross-band remote bases at high locations. A PL'ed signal opens
the RX, but then a non-decisive capture of multiple non-PL signals
compete for the RX.]<br>
<br>
<br>
<br>
I think the only practical way for this to work is to have the UHF
system be a full-blown standard UHF-to-UHF repeater, with an auxiliary
transmitter on 144.39. Use one PL tone on the user's mobile to repeat
to 144.39. Use a different tone to repeat to UHF. <br>
<br>
Now when the mobile user hears voice alert from this system on 144.39,
he just selects a standard UHF repeater pair on the other side of the
radio, and talks back like any other repeater to coordinate the QSY.
You would have two adjacent memory slots on the UHF half of the radio
with the identical freq and splt--- one with the PL tone to key the
144.39 TX downlink, and one with a different PL tone for the normal UHF
repeater.<br>
<br>
After all, just this week, you commented about discovering how nice
conducting voice ops on UHF was, while the APRS goes on without
conflict on VHF. <br>
<br>
<hr size="2" width="100%"><br>
--<br>
<br>
Stephen H. Smith wa8lmf (at) aol.com <br>
EchoLink Node: WA8LMF or 14400 [Think bottom of the 2M band]<br>
Skype: WA8LMF<br>
Home Page: <a class="moz-txt-link-freetext" href="http://wa8lmf.net">http://wa8lmf.net</a><br>
<br>
JavAPRS Filter Port 14580 Guide <br>
<a class="moz-txt-link-freetext" href="http://wa8lmf.net/aprs/JAVaprsFilters.htm">http://wa8lmf.net/aprs/JAVaprsFilters.htm</a><br>
<br>
"APRS 101" Explanation of APRS Path Selection & Digipeating <br>
<a class="moz-txt-link-freetext" href="http://wa8lmf.net/DigiPaths">http://wa8lmf.net/DigiPaths</a> <br>
<br>
Updated "Rev H" APRS <a class="moz-txt-link-freetext" href="http://wa8lmf.net/aprs">http://wa8lmf.net/aprs</a><br>
Symbols Set for UI-View, <br>
UIpoint and APRSplus:<br>
<br>
<br>
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