[amsat-bb] Re: Doppler Tuning Convention Question

Tim - N3TL n3tl at bellsouth.net
Tue Jun 1 07:49:52 PDT 2010

Hi Alan,

Your comments suggest that I'm the one in Bizarro World. 

Regarding the One True Rule - I operate under the impression (which, I thought, has been backed by science) that regardless of the frequency pair, Doppler always will have a more pronounced effect (in relative terms, of course, based on the frequencies being used) on the higher of the two. In a perfect world, ever operator will be tuning for Doppler the same way. reality, of course, is that some people either can't use computer-aided Doppler tuning (my situation for the first several months that I worked the linear satellites) or they choose not to - as I still often do. And when I do, I will continue to compensate - most - for the frequency being most affected by Doppler, which is the higher frequency.

Regarding mid-pass - My experience suggests that, while your statement about mid-pass Doppler shift is accurate, it does not take into account that mid-pass occurs for only a moment in time during any orbit. My experience has been that the lower a satellite's orbit, the more significant Doppler movement will be. VO-52 is the prime example, in my opinion. And here, for me, the time just before and just after (say, 20-30 seconds on each side) mid-pass is when Doppler affects the uplink frequency the most. The computer and software I use often have not been able to adjust my radio's frequency as quickly as they need to in order to compensate for Doppler. Others may not have that problem with their computer-tuning system, but I believe the more-rapid Doppler effect is consistent for VO-52 regardless of how one is tuning. I'm confident (and, actually hope) that others will correct me if I'm wrong about the relative speed of Doppler correlating to the relative
 height of a satellite's orbit.

Regarding pride associated with the decision to not use current technology - Any measure of pride I take from knowing how to routinely tune for Doppler manually comes from the knowledge that circumstances and situations may arise when I will be asked to communicate effectively through the satellites without access to everything associated with current technology. My station is founded in that concept. I don't have an all-mode, full-duplex radio. I use two radios with a diplexer connecting them to one antenna. I don't have an az/el rotator; well, actually I do. It has three parts - shoulder, elbow and wrist. I don't have two very large, high-gain antennas. The only satellite antenna I own and use (other than some whips for the HTs) is the Elk dual-band log periodic. All of that being said, I am proud to say that I can use the gear I have to work any of the current fleet of single-channel-FM and linear-transponder satellites from anywhere - even without
 access to a computer or even to power. In that regard, Patrick - WD9EWK - has been an inspiration and mentor. His station is similar to mine.

I can't comment on your last two statements (about SSB vs. FM satellites and how to appropriate use a Yaesu FT-736r) because I didn't comment initially on either one. Personally, I find the FM satellites easier to work than the birds with linear transponders - but the latter are easier to make contacts on because they never attract nearly the number of operators on a single pass as the FM satellites. NONE of them are as difficult to work as I believed. They represent the most fun and satisfying operation I've ever done in amateur radio.

73 to all ... from the EM84 chunk of Bizarro World....

Tim - N3TL

From: Alan <ve4yz at hotmail.com>
To: amsat-bb at amsat.org
Sent: Tue, June 1, 2010 9:31:36 AM
Subject: [amsat-bb] Re: Doppler Tuning Convention Question

Folks I've been patiently silent reading this déjà vu annual discussion and
I'm getting a brain crap.

- comments that tuning the highest frequency is the "One True Method"
Yikes! Why is that?  So you can leap frog down the pass band and eventually
stomp all over a QSO where folks are tuning both TX and RX to maintain a
single constant frequency at the satellite?

I've read the " Doppler tends to move more quickly near mid-pass than the
computer and software routinely seem able to keep up".  Mid pass is when the
sat is moving most tangentially to you at which point Doppler shift is nil.

I've read statements from many taking pride in their lack of use of current

I've read that working tight SSB sats is easier than the wide band FM where
the satellite is very forgiving of your sloppy tuning. 

I've read advise to someone using an FT 736r that your shouldn't tune the RX
and ignore the use of the NOR/REV feature, again so you can eventually stomp
on other QSO's as you slide down the pass band.

Have I just been transported into a Bizarro World?

73, Alan VE4YZ
AMSAT LM 2352 
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