[amsat-bb] Re: AO-51

Alan Sieg WB5RMG wb5rmg at somenet.net
Wed Dec 10 06:31:13 PST 2008

>> I would expect . . . .
> I may be misunderstanding your statement, but transmitters in different
> locations on the ground will show different curves. Remember you have
> Doppler on both the uplink and downlink too, so the beacon should be
> different than any uplinked signal (unless someone was running full Doppler
> tuning).
> 73, Drew KO4MA

Point well taken Drew - Thanks for your thoughts.
I figured there would be some slight differences in uplink doppler as
a function of ground location relative to TCA. Comparing the other traces
to that of the presumed beacon, there appear to be two slopes - either
matching closely or not. That made me suspect an additional transmitter.
The 145 MHz doppler I would expect to be less pronounced than the 435 ...
I suppose with a really clean display and accurate measurements and .. .. ..

I'm sure that an entire team of experts is involved in this type of
spectral fingerprinting every day. Wish I had more time and tools, it
could be a lot of (admittedly geeky) fun.    Unfortunately the only
waterfall I can get is an audio passband-width ala MixW or similar. The
wideband waterfall you showed looks like an interesting tool. I'm envious.

Anyway, changing the uplink solves the immediate issue, but still leaves
the question - could it have been a terrestrial carrier, relayed by FO-29
or possibly a spur from some other transmitter on a different bird...
The fact that you saw energy on that frequency, with doppler could
fairly well rule out a ground-based signal on the 145 MHz uplink, reckon ?

  Thanks  /;^)
  <- Licensed in 1976, WB5RMG = Alan Sieg * AMSAT#20554 ->
  <- http://www.somenet.net * http://wb5rmg.somenet.net ->
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