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Something OLD, Something NEW


The suggestion to point the antenna at the ground and then at the sky and
observe the noise differential. A great suggestion to help evaluate your


How do I know when my receive system is "as good as it can get" ?

Simple...no test equipment required.

When you can clearly hear the "passband" noise of the satellite itself, no
further improvement will help. Until you can hear it clearly....your system
is not as good as it can get.

How do you hear passband noise?

First...when there is some spin mod on the bird, listen to a white noise
area (no signals). If you don't hear any swishing up and down of the noise
in the background....you're not hearing the passband noise. The passband
noise should be "spin modulated" at the same rate the main beacon is being
"spin modulated". You should be able to clearly hear the swoosh, swoosh,
swoosh. This will only happen as AO-40's antenna is "off pointed" or
squinted. Don't look for it at apogee...it won't be there.


When the bird is at apogee and we have no spin modulation to listen to, tune
down or up the band far enough to drop off the "edge" of the transponder's
bandwidth. Your noise should drop significantly when you hit the edge "going
away" and rise abruptly when "coming back" into the passband.

If you can't hear the passband noise CLEARLY, when you do either of these
two experiments, your receiver downlink is inadequate, period.

Once you can hear several dB of consistent passband noise at apogee, you
will know that there is nothing you can do to make things better...you've
reached the PINNACLE of receive performance.

When we used AO 10 and 13, we used to see 1 to 3 S-units of passband noise,
with an antenna mounted preamp (gasfet, 25 dB gain)  and KLM 14C crossed



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