[amsat-bb] Re: AO-51 short experiment
Alan P. Biddle
APBIDDLE at UNITED.NET
Sun Oct 24 13:45:18 PDT 2010
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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