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Some doppler observations/questions

I am using HRD with Sat tracker module (thanks, Simon!)

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.  

How can I consistently determine this offset so I can include it in with the
Doppler correction?  Or is it on a case-by-case basis?

PS Thanks, Frank, K9CIS, for the nice CW rag chew on FO29 tonight.  

Mark Lunday

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