[amsat-bb] Re: Satellite tracking programming ideas
w9ae at charter.net
Fri Jan 18 14:31:00 PST 2008
Phil, you correctly point out that full Doppler tuning can sometimes
have errors due to either the earth station or the satellite frequency
drifting slightly. The best solution to compensate for the drifting
depends on WHAT is drifting. In my case, I know my FT-847 435 MHz
transmit frequency drifts a few hundred Hz during a long transmission.
Consequently, as my transmitter slowly drifts, I turn my FT-847's Sub
Tune knob to keep my uplink signal sounding good on the Doppler-tuned
downlink. The Sub Tune knob adjusts SatPC32's TX offset.
Alternatively, I can click the + and - keys on my keyboard's number pad
as required to adjust TX offset in 100 Hz increments. Or I could press
the - and = keys to tune TX offset in 10 Hz increments.
If your receiver or the satellite's transmitter is drifting, I suppose
you should click the CAT menu and use the Downlink Calibration
adjustments. Then, in theory, you can tune across the transponder and
enjoy perfect automatic Doppler correction. In practice, I frequently
have to tweak my TX offset to keep my signal sounding good on the
Doppler-tuned downlink, and I often tune manually to chase the downlink
from stations that don't use automatic Doppler tuning.
Wayne Estes W9AE
Oakland, Oregon, USA, CN83ik
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