[CRAPRS] Alternate APRS frequencies or experiments

[Jerry Pasker]

>Posting from the CRAPRS mailing list:
>
>I just recently setup my Igate at home for a 
>temporary test for a friend.  Now that the test 
>is over, it just sitting idle.  I have been 
>thinking about alternate frequencies and such 
>for APRS tests.  Listening to 144.39 now you 
>hear a lot of those 10- 20 watt trackers, not 
>many of the 1/4 watt QRP trackers anymore.  I 
>live close enough to the main digi in town 
>(Hiawatha) there is about 100% coverage of my 
>area.

Was it stand alone, or through your PC?


>I have hard talk of the following alternate 
>frequencies for trackers, and wondered if 
>anybody else is experimenting with alternate 
>frequencies, or something other that the 
>standard 144.390 stuff?
>
>Here is a quick list of the frequencies I have 
>seen listed looking thru the various email 
>newsgroups , but I have yet to hear anybody else 
>on any of them.  Anybody else running alternate 
>frequencies?
>
>50.620 (FM) 1200 baud 6 meter band (simplex)
>
>144.390(FM) 1200 baud 2 meter US (simplex)
>144.990(FM) 1200 baud secondary US (simplex) Nobody heard here

That's because you can't hear my 1 watt tracker 
from Hiawatha when I occasionally play on 
144.990.  :-)

It wasn't until I was digipeating my little 
tracker with a port-o-digi that I realized the 
144.990 and 144.390 offset was 600khz so low 
power stuff can be transmitted on to 144.390 
easily. Someone was thinking when they suggested 
that alternate frequency.

The drawback is that when digipeating like that, 
the digi is deaf on 144.390 and a 1 sec carrier 
tone before data is required to keep everyone 
else off the 144.390, assuming they are nice and 
listen before transmitting. (explanation follows)

I do the same 1 sec carrier thing on KD0EWX on 
144.390.  The 1 watt radio is deaf and transmit 
only, so a 1 sec carrier before data stomps on 
any occurring transmission long enough that those 
transmissions can finish, (probably unimpeded due 
to the low power level of the tracker) and then 
no one else jumps in until the tracker is done. 
I've found it's the only way a deaf 1 watt 
tracker can get packets reliably in to the 
network, otherwise it tends to be hit and miss. 
It does lots of corner pegging, and adaptive 
speed transmitting, so it's not abusive.   Seems 
to work great around here, and well in major 
metro areas as well.

I do the same thing on the balloon tracker.  But 
it's on a 57 sec transmit cycle, so it is much 
more abusive to the network. At altitude, it 
*WILL* be doubling with other ground 
transmissions, and at altitude, it *will* hear 
everything all over the ground so it *has* to 
transmit blind (deaf) or it'll never be able to 
get a packet in to the network.  The only way to 
do that is to intentionally have it QRM for 1 sec 
so everyone else in range finishes transmitting 
and then stays quiet until the tracker transmits. 
But it doesn't fly often.  I do the same on my 
wearable tracker, (...that I never wear...). but 
being 1 watt  and low to the ground, it never 
gets more than a handful of miles to a digi, 
(always mine anyway) so it has a very very local 
affect, so again, I don't feel guilty about it.

Intentionally QRMing for 1 sec, doubles the duty 
cycle of the transmitter, so I justify it by 
transmitting half as much.  Either with good 
adaptive transmitting (corner pegging, speed 
changes, etc) or by just plain doubling the 
transmit rate.


-Jerry