David Palmer wrote:

I seem to have to adjust ± 100 to 200 Hz at the start of the pass, and periodically during the pass, to keep my return pitch constant.

Wayne replies:

I have to make similar corrections when SatPC32 tunes my FT-847. One likely cause is that the radio's local oscillator drifts slightly when transmitting due to heat generated by the transmitter. My FT-847 transmit frequency drifts noticeably when I transmit on 435 MHz with high power. It drifts less when I transmit at low power. Unless your radios have high-stability oscillators I think it's normal to need to correct the frequencies by 100-200 Hz.

From one pass to another, the local oscillator on the satellite might also drift slightly due to changes in temperature.

Wayne Estes W9AE Oakland, Oregon, USA, CN83ik