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

[Luc Leblanc]

On 15 Nov 2008 at 23:57, Mark Lunday, WD4ELG wrote:

> 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

I am starting to implement automatic doppler control and i note the same effect. I guess it is related to the step of adjustment. I am 
using 10 hertz and i think especially at TCA on vertical elevation pass the 10HZ step is not enough i have to manually adjust to compensate 
for this lag. I will try to use higher step.


"-"


Luc Leblanc VE2DWE
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www.qsl.net/ve2dwe
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