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f4exb / sdrangel

SDR Rx/Tx software for Airspy, Airspy HF+, BladeRF, HackRF, LimeSDR, PlutoSDR, RTL-SDR, SDRplay and FunCube
GNU General Public License v3.0
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BUG: SDRangel Satellite Tracker, Doppler shift calculations have issues #1448

Closed gvimlag closed 2 years ago

gvimlag commented 2 years ago

TWO PROBLEMS: 1) When an NOAA satellite passes overhead, part of its pass should show a POSITIVE Doppler shift and the other part should show a NEGATIVE Doppler shift. Unfortunately, the APT Demodulator always shows a NEGATIVE Doppler shift (negative Delta-Frequency) during an NOAA satellite pass. It never shows a POSITIVE Doppler shift.

2) The Doppler shift adjustment should center the receiver frequency band around the satellite transmission. In the case where the correct Doppler shift is negative, the receiver frequency band is NOT centered around the satellite transmission.

The only user adjustment to Doppler shift that I've found is the default frequency used to calculate Doppler shift. I've manually adjusted the default frequency to the middle of the NOAA transmission range (137.5 MHz), to minimize Doppler calculation errors:

    Show settings dialog
      Display
        Default frequency (MHz): 137.500

Unfortunately, this change has no noticeable effect on the above issues.

So both the direction of the Doppler shift and its centering appear to have issues.

Please correct the Doppler shift processing in the Satellite Tracker.

srcejon commented 2 years ago
  1. When an NOAA satellite passes overhead, part of its pass should show a POSITIVE Doppler shift and the other part should show a NEGATIVE Doppler shift. Unfortunately, the APT Demodulator always shows a NEGATIVE Doppler shift (negative Delta-Frequency) during an NOAA satellite pass. It never shows a POSITIVE Doppler shift.

Just gave it a try for the pass 5 minutes ago here, and there was a positive shift for me, so I think I'll need some more details from you. Please can you send your (approx) lat, long and time zone with details of the satellite and time the pass went wrong, I'll try to recreate it. A screenshot of it going wrong would probably also be useful.

gvimlag commented 2 years ago

I withdraw my bug report: BUG: SDRangel Satellite Tracker, Doppler shift calculations have issues (Issue #1448)

I reinstalled the OS's on both the client and server machines, plus recompiled SDRangel. After these updates, I tested the Satellite tracker with all three NOAA satellites using a mix of local and remote Soapy devices. The Doppler shift now works correctly in all cases.

I apologize for wasting your time.