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

[mlunday@nc.rr.com]

Thanks to all who replied!

For HRD, how would I enter this offset?

---- Alan Cresswell <alancresswell at xtra.co.nz> wrote: 
> Hi Mark,
> 
> Almost all the linear sats have some offset due to variations in frequency
> of the internal oscillators etc.  In the case of AO-07 the offset is
> temperature related and varies slowly depending on the amount of sunlight
> etc.  (AO-07 at the moment is about 4.5kHz) The technique I use to determine
> the offset at any time is to set my receiver to the centre of the satellite
> downlink passband (+/- Doppler) and then adjust my transmitter frequency to
> hear myself correctly on the downlink.  The difference between my actual
> uplink (+/- Doppler) and the nominal centre of the uplink passband is the
> offset. I save this value and use it built into my Doppler correction until
> any change warrants a re-calculation.
> 
> Alan
> ZL2BX
> 
> 
> 
> -----Original Message-----
> From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
> Behalf Of Mark Lunday, WD4ELG
> Sent: Sunday, 16 November 2008 04:58
> To: amsat-bb at amsat.org
> Subject: [amsat-bb] 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
> WD4ELG
> wd4elg at arrl.net
> http://wd4elg.net
> 
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