[amsat-bb] Re: How you do DOPPLER correction in Linear Transponders?
n3tl at bellsouth.net
Thu Jul 2 10:29:41 PDT 2009
The latest edition of "The ARRL Satellite Handbook" contradicts earlier versions, which suggested the same approach that Drew has here (i.e., always Doppler-tune the higher frequency) in favor of "parking" the uplink frequency and Doppler-tuning the downlink (see the section "Finding Yourself ... and Others," which begins on page 5-13 of the handbook). It occurs to me that, in general, that is the worst approach to take - although I admit to only knowing enough about all of this to be more dangerous than not.
Before I added computer-aided Doppler tuning to my station, I took Francesco's approach and always tried to stay at the same downlink frequency, Doppler-tuning the uplink regardless of whether it was the higher frequency. In reality, my approach is only inconsistent with Drew's ONLY on FO-29 because, on AO-7 (when in Mode B) and VO-52 (always in Mode B), the uplink IS the higher frequency.
The reason I believe the 2008 edition of "The ARRL Satellite Handbook" offers the worst approach has two elements:
1 - the "slipping" on the downlink that Francesco alludes to in his post, and
2 - the use of VO-52 as the "example satellite" for the description of how to find one's signal. The exercise directs readers to Doppler-tune the lower of the two frequencies to find themselves on the satellite.
Later today, I will try the "always tune the higher frequency" rule on FO-29, which I admittedly have not every tried. I'm looking forward to learning how that works for me since the higher frequency on that satelite is the downlink.
73 to all,
Tim - N3TL
-------------- Original message from Fabiano Moser <fabianomoser at gmail.com>: --------------
> Dear friends,
> We know that some Satellite Operators use diferent system to doppler
> For Linear Transponder
> 1) Adjust uplink and downlink automatic by CAT? (Not always woks, some times
> I´m up or down from the computer adjust)
> 2) Adjust uplink and downlink manual
> 3) Keep Uplink fixed and adjust only the Downlink frequency.
> What is the more indicate method to use?
> FT-847 have knob to adjust Uplink without change downlink VFO, and I´m using
> it to keep my voice in downlink at same downlink much I can.
> But I know some operators use fixed uplink.
> How you do?
> Fabiano Moser CR7/PY5RX
> ARISS-PORTUGAL (Amateur Radio on the International Space Station)
> Representative at Teleconference and Portugal Telebridge Coordinator.
> "There is no great talent without great will. (Honoré de Balzac)"
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