[amsat-bb] Re: AO-51 short experiment

Bob Herrell nk7i at yahoo.com
Sun Oct 24 15:02:24 PDT 2010


I agree with you totally. It is going to be an ongoing problem and unless 
individual operators take responsibility for their emissions, it is going to 
continue. Even with coordination the frequency is still not owned by any 
particular station. It is just  common courtesy that we need to show to each 
other. Are these APRS stations just beaconing in hopes of hitting the ISS or are 
they in use for normal APRS? I don't see 145.825MHz being used as a terrestrial 
frequency. I can understand the problem when HO-68 and the ISS are in the same 
footprint, but to run a station continuously on 145.825MHz is crazy. I do send 
packets to the ISS myself, but ONLY when it is in view and turned on. It all 
boils down to the old idea of "Listen before you talk".


From: Alan P. Biddle <APBIDDLE at UNITED.NET>
To: Bob Herrell <nk7i at yahoo.com>; amsat-bb at amsat.org
Sent: Sun, October 24, 2010 3:45:18 PM
Subject: RE: [amsat-bb] Re: AO-51 short experiment


145.825 is the "established" space APRS frequency, and has been/is used by
more than just the ISS for years.  There are other APRS satellites which are
intermittently active on the same frequency, and I expect there will be
others in the future.  I can't address the formal coordination issue, but
anything with an uplink on that frequency is guaranteed to have problems.
The only question is whether those problems are tolerable.  There is little
to no APRS activity on that frequency over most of the world, and then there
is the question of both HO-68 and the ISS being in the same footprint.  The
HO-68 has an inclination of about 102 degrees, the ISS about half that.
Finally, the ISS is not active on that frequency 24/7.  It operates on other
frequencies for voice and SSTV, and is often QRT completely due to other
operations.  In an imperfect world, it looks like a reasonable tradeoff,
though other evaluations are certainly possible.

The problem of unattended APRS beacons does cut both ways.  There are some
daylight-only APRS satellites.  When they enter periods of extended
illumination, they can be commanded from their default modes.  However, even
a single "braaap" can pull the DC busses low enough that the command
stations need to start over again.  WB4APR has lamented this problem, with
specific calls, in other venues.  Looking at some of the paths, both in
Drew's example and my reception, there are stations whose paths have not
been updated for years.  

The sort of courtesy/coordination issue is not limited to space operations.
A ham relatively local to me fired up a propagation beacon on 30 meters this
month.  It is/was within 200 HZ of an APRS frequency which has been in use
for some time.  Quite a fight over who "owns" the frequency.  ;)



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