Re: [amsat-bb] Crystal Ovens

["Bill Magnusson" <williamb@xxxxxxxxxxx>]

>
>I have a S-band downconvertor (several years old, from DEM).
>This uses a 94 MHz crystal in a HC/18 case.
>I'm concerned about the frequency drifting around, especially
>when trying to keep my telemetry demodulator locked on
>to the telemetry signal.

>
Doug,

I have the same unit.

There is a short-term drift on the signal caused by Doppler as the
spacecraft spins. This has been making precise tuning almost impossible. It
will improve as the squint-angle improves.


My solution to long-term drift is to keep the downconverter in the shack and
run good co-ax up to the pre-amp on the dish feed. Since then I haven't
noticed any long term drift at all.

I haven't decoded anything since ao-40 has been on after the mishap. Signal
has been far too weak. I can only hear the beacon at odd times and then only
for perhaps a quarter-hour and it disappears into the noise again. Using a
DEM pre-amp on a 4ft dish with G3RUH design feed. Prior to the mishap the
2.4GHz signal was up to 7 "S" units above my noise floor.

Bill...vk3jt
Milawa
Australia


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