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Re: doppler.



Hi All,
        Re: doppler. I've attached K4GMJ's article from the August 1992 
issue of Oscar News. It may be of interest to those, like me, who still use 
old equipment.

In addition to Maury's notes, I can mention, I have used an NE 567 tone 
decoder IC and a LED as the visual receiver with a simple twin-T audio 
oscillator for the transmitted signal.
A simple twin-T osc: is better than an NE555 in this application.

I still operate with the Yaesu 290/790 pair + associated homebrew aerials 
and amps (over 20 years now) and manage quite nicely on VO-52 with 
InstantTUNE. When set up correctly, the signals track perfectly so even with 
"old" equipment it's still possible to adhere to THE ONE TRUE RULE regarding 
doppler.

I don't tune at all for doppler on AO-7.

Occasionally, just for fun, I tune manually ... (transmitter and receiver) 
.... to keep the frequency constant at the satellite, however ... be aware 
.... it is *NOT* mandatory to keep the signal fixed at the satellite. Many 
operators still use the manual convention of tuning the highest frequency 
.... (because it has the highest doppler rate).

This is perfectly acceptable because not everybody is either 1) affluent 
enough to be able to afford the latest all singing, all dancing multimode 
rig ... or 2) not experienced enough to cope with doppler on the uplink and 
the downlink at the same time.

73 John.   <la2qaa@amsat.org>

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