[amsat-bb] Re: Some doppler observations/questions

Simon (HB9DRV) simon at hb9drv.ch
Sat Nov 15 23:29:43 PST 2008

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

----- Original Message ----- 
From: "Mark Lunday, WD4ELG" <mlunday at 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.

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