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