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G0FTD > DOPLER 05.03.06 17:24l 32 Lines 1182 Bytes #999 (0) @ EU
BID : BE4020G0FTD
Read: GUEST
Subj: Re: GB3VHF Rebuilt Beacon Accuracy
Path: DB0FHN<DB0FOR<DB0SIF<DB0EA<DB0RES<DB0GOS<ON0AR<ON0AR<GB7YKS<GB7SYP<
GB7LGS<GB7ESX<GB7NNA
Sent: 060305/1239z 00754@GB7NNA.#31.GBR.EU $:BE4020G0FTD [Witham, Esx]NNA V3.1
GM7HUD wrote:-
> The discrepancy in your measurements will come from your receiver LO
> accuracy, which in absolute terms you probably have measured and you'll
> also so know its temperature drift etc.
>
> So the only thing we don't know is how accurate the sample clock is in your
> PC. It should be 11025kHz for WSJT IIRC, so I would suggest that the source
> of the error is in your PC.
Not long after I sent the doppler bulletin I played some more to see
what WSJT is doing. I noticed that the reported doppler shift merely
varied each time I altered the VFO, so WSJT has to assume that the JT65B
synch tone really is correct in the first place and then applies any
offset as doppler shift, which it isn't.
I was hoping that some unknown (to me) system was being used - but no
chance :-(
I reckon to make things work properly you need the tx and rx at both ends
of the link synched and locked to the same source for doppler feature to
work properly.
So the bottom line is the doppler info should be disregarded - it's
meaningless and John can feel confident his results are correct.
Ah well - the experiment kept me amused for half an hour.
Lesson complete.
- Andy -
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