[amsat-bb] ARISSat telemetry and Doppler tuning

[Ronald G. Parsons]

Last evening, after having several days experience capturing ARISSat telemetry, I sat at my radio and watched carefully how SatPC32 and ARISSatTLM played together. I had settled on a tuning correction value of –540 HZ to get the CW signal to center around the CW tuning point as the Doppler correction was handled by SatPC32.

The approach of the satellite seemed normal. but as the satellite passed by, I noticed the CW signal average “position” to be creeping upward, needing a reduction of the tuning correction by about 40 Hz to –500 Hz. This lasted for a couple minutes and then the CW signal started creeping down and I had to go back to my –540 Hz value.

The first explanation I could think of is that the Doppler correction computed by SatPC32 from my position and the keps was in error. But of course, it could have been a change in my radio (unlikely as it had been on for hours) or a change in the frequency of the CW signal from the satellite.

I’ll keep watching this and wonder if others have noticed something similar.

Ron W5RKN