A couple of ideas:
1) Make sure your Lat / Lon is correct - very correct. 2) Make sure you use good Kepler data, for example from www.celestrak.com .
I test with the CW beacon on LO-19 - if the pitch does not change during a pass then the Doppler is spot-on.
I also notice offsets with some sats - as other have commented this is the LO on the satellite although it could also be the LO on the radio.
Simon Brown, HB9DRV www.ham-radio-deluxe.com
----- Original Message ----- From: "Mark Lunday, WD4ELG" mlunday@nc.rr.com
I notice that for the non-FM birds I am working (AO7, FO29, VO52) the Doppler is never quite exact. Or I guess I should say there seems to be a constant *offset* that needs to be included in the Doppler calc. Tonight on AO7 mode B pass, my actual downlink frequency seemed to be about 4 kHz lower than what it should be according to the Doppler. As the bird passed by, I followed the "one true rule" and only adjusted the higher freq (uplink in this case). It was consistently about 4 kHz lower.
On FO29 pass, there seemed to be about a 2 kHz offset. When the bird passed overhead, the Doppler "flipped" quickly and I had to find my signal again.