[amsat-bb] Full Doppler Tuning

Ronald G. Parsons w5rkn at w5rkn.com
Wed Sep 29 12:31:33 PDT 2010

My July/August 2010 issue of The AMSAT Journal arrived today and I was pleased to see the article by Alan Biddle on Doppler Tuning. This has long been a pet project of mine since Paul Williamson, KB5MU, published his article "The One True Rule for Doppler Tuning" in the OSCAR Satellite Report, January 1994 and my article "A Recommendation for Doppler Tuning" in the March/April 1996 issue of The AMSAT Journal.

I was especially pleased by Alan's call for satellite tracking programs that control your transmitter and receiver to display the "frequencies at the satellite." This should be very easy for the developers of the software to do. For example, in SATPC32 (an ad for which appears on the last page of Alan's article), the  "frequencies at the satellite" are almost displayed now. In the center of the window, just below the menu bar, are displayed the Receive and Transmit frequencies (at your location) and just below these are the Doppler correction values from the "frequencies at the satellite." Algebraically subtracting the lower (Doppler correction) value from the upper (your site frequency) values yields the "frequency at the satellite."

It would seen to me that the program should display the "frequency at the satellite" as the frequency of your receiver and transmitter are most likely already displayed on your rig. How about it, you software developers? At least give your users the option of which value to display in your window.

As an aside, speaking of Doppler shifts, I (along with K5EWS and others) are currently working on a method of tracking model rocket flights using an inexpensive UHF transmitter (925 MHz CW in my test case) in the rocket and, using several receiver sites, analyze the Doppler shift of the transmitted signal and use the mathematics of Trilateration to determine the location of the rocket in 3-space. Our first full scale test is this coming weekend.

Ron Parsons W5RKN

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