[amsat-bb] Re: How you do DOPPLER correction in Linear Transponders?

n3tl@bellsouth.net 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 
> control. 
> 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? 
> -- 
> 73 
> Fabiano Moser CR7/PY5RX 
> ARISS-PORTUGAL (Amateur Radio on the International Space Station) 
> Representative at Teleconference and Portugal Telebridge Coordinator. 
> http://www.amrad.pt/ariss.php 
> "There is no great talent without great will. (Honoré de Balzac)" 
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