[amsat-bb] Re: Satellite tracking programming ideas

[Wayne Estes]

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