[amsat-bb] Re: Doppler Tuning Convention Question

Edward R Cole kl7uw at acsalaska.net
Tue Jun 1 11:58:00 PDT 2010

Just a quick comment on Doppler effects.  Doppler 
offset from the resting frequency is observable 
only on the radial velocity component of the 
satellite and that is usually most significant at 
AOS or LOS.  BUT what the operator is usually 
responding is to the rate of change of Doppler 
and not the absolute value of the frequency 
offset.  Doppler rate change may occur more at mid-pass than elsewhere.

Regarding the "one true rule" that is generally 
only accomplished by software tuning both uplink 
and downlink simultaneously, the manual method of 
tuning the higher frequency will never mesh 
exactly with the other mode.  FM should be more 
forgiving of Doppler shifts due to the 15-KHz 
bandwidth of the signal.  Some radios even have 
AFC to maintain change in frequency in the FM mode.

Higher frequencies show more Doppler and the rate 
of change will also be proportional.  Thus the 
difficulty manual tuning mode LS for Leos.

73, Ed - KL7uW

At 06:49 AM 6/1/2010, Tim - N3TL wrote:
>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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>Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
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73, Ed - KL7UW, WD2XSH/45
BP40IQ   500 KHz - 10-GHz   www.kl7uw.com
EME: 144-600w, 432-100w, 1296-60w, 3400-fall 2010
DUBUS Magazine USA Rep dubususa at hotmail.com

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