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RE: AO40 Doppler



At 08:53 AM 5/28/2002 +0100, Howard Long wrote:
>I also find that, for instance, the Doppler frequency predictions from
>IT+InstantTune, Nova and Wisp+WispDDE are rarely in agreement, sometimes out
>to a couple of kHz.

That's disturbing. If they all disagree, at most one of them can be right.

In a spot check of Nova 2.1r, InstantTrack 1.55, WiSP GSC 2.03, and a manual calculation, they all agree pretty well except Nova. Nova's numbers were just wrong, showing about 17 kHz of downlink Doppler where the other calculations showed 21 kHz (AO-40 S2 downlink, San Diego observer, around 2002-05-28 16:40 UTC, latest AMSAT keps), even though the satellite coordinates and range values agreed among all the programs.

That's just one data point, but it seems to indicate that Nova's newish Doppler calculations might still have some bugs.

In particular, that number (17 kHz) looks like the Doppler shift on the *difference* between the uplink and downlink frequencies. That would be the right number for tuning radios on the transponder, but as shown by Nova it's clearly intended to be just the downlink Doppler, since the uplink Doppler is shown separately.

73  -Paul
kb5mu@amsat.org

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