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Author Topic: Doppler Shift  (Read 257 times)

W9AC

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Doppler Shift
« on: July 21, 2021, 11:33:48 AM »

Today, I was monitoring changes to transmit Doppler shift of CAS-4B using SatPC32 software.  As expected, as CAS-4B approached my QTH, the frequency increases.  However, as the satellite passed nearly overhead, I was expecting to see a downward frequency shift reversal but that didn't happen until CAS-4B's footprint was far away, well past the Caribbean.  Can someone explain why there's not a frequency reversal at the time the satellite is overhead?

Paul, W9AC
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AB5R

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Re: Doppler Shift
« Reply #1 on: July 21, 2021, 12:25:06 PM »

I suspect that the dropout "may" have been due to the type of antenna that you may have been using.  You didn't specify what you antenna system was at that time.  Or, possible geographical blockage to your site.  Do you have horizon to horizon vision?

73,
Jerry AB5R
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W9IQ

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Re: Doppler Shift
« Reply #2 on: July 21, 2021, 02:29:00 PM »

Paul,

The Doppler shift should pass through 0 and change signs as the satellite passes through your observer maximum elevation angle and the closest location to you.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W9AC

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Re: Doppler Shift
« Reply #3 on: July 21, 2021, 02:59:59 PM »

Paul,

The Doppler shift should pass through 0 and change signs as the satellite passes through your observer maximum elevation angle and the closest location to you.

- Glenn W9IQ

Glenn,

That's what I thought too.  Time to validate settings in SatPC32.  Thanks.

Paul, W9AC
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W9IQ

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Re: Doppler Shift
« Reply #4 on: July 23, 2021, 08:17:09 AM »

Perhaps your keps are out of date, Paul? Or another thought - I had a minor problem for a field day activation because I forgot to change my coordinates even though I was in the same general area.

- Glenn W9IQ
« Last Edit: July 23, 2021, 08:27:39 AM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.
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