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Re: Doppler



In a message dated 9/11/01 8:03:31 AM GMT Daylight Time, 
owner-AMSAT-BB-digest@AMSAT.Org writes:

<< Set me straight!
 
 I always thought that the frequency increased as the object approached and
 fell as the object went away.
 
 Well, I picked up the bird (AO-40) tonight at about MA 6 or so. The beacon
 freq was falling fast as the bird started to streak away, as I would expect.
 Then at about MA 15-20 I suddenly noticed that the freq was going UP and
 continues at this time (MA-26). Nova continues to say that the range
 continues to increase (About 28,500km), thus I would think that the freq
 should continue to fall until apogee, at which time the range would start to
 fall and the freq would start to again rise.
 
 Is there something I don't understand, or am I seeing a massive drift in my
 UEK-3000 DC? >>

How about this? (figures not accurate but OK for explanation)

1) doppler will always be more accurate than any tracking program.
2) It's all relative......

e.g.
If the combined effects of satellite orbit and earth rotation at MA10 mean 
that, relative to you, the satellite is moving away at 500m per second then 
the beacon may appear to be  20 kHz below the actual frequency.
Now if at MA50 the relative movement is reduced to moving away at 250m per 
second, the doppler shift will move the beacon to just 10kHz below the actual 
frequency.

So...the rules of doppler shift have been obeyed, in that the beacon is still 
lower than the actual frequency. However, using the example above, you have 
heard the beacon increase from 20k below to 10k below its actual frequency.

Hows that?

73

David  G0MRF
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