I am composing a presentation about FM sats, hopefully to be given in a few months at a hamfest. How to remember which way to compensate for doppler: Always adjust the higher frequency. For V/u or U/v sats, this means adjust the 70cm side and leave the 2m side fixed. Which way to move it? Very easy to remember. If 70cm is the UPlink, you'll adjust your transmit frequency UPward through the pass. If 70cm is the DOWNlink, you'll adjust your receive frequency DOWNward through the pass.
I think others have basically explained why.
Dave AD7DB
If 70cm is the UPlink, you'll adjust your transmit frequency UPward
through
the pass. If 70cm is the DOWNlink, you'll adjust your receive frequency DOWNward through the pass.
I showed a quick slide with the Doppler equation on it ... that delta-lambda stuff. Then I told them pretty much what you said ... and I could hear a "Phew!" from the audience.
-- 73 de JoAnne K9JKM k9jkm@amsat.org
...and of course there is no reason NOT to adjust the lower frequency especially if it is computer controlled. It's just that lower frequencies do not change as much for a given satellite speed (see JoAnne's Doppler equation to determine why :-). And as someone said, the FM capture effect makes it even less important.
On Thu, Jun 6, 2019 at 12:01 PM JoAnne K9JKM via AMSAT-BB < amsat-bb@amsat.org> wrote:
If 70cm is the UPlink, you'll adjust your transmit frequency UPward
through
the pass. If 70cm is the DOWNlink, you'll adjust your receive frequency DOWNward through the pass.
I showed a quick slide with the Doppler equation on it ... that delta-lambda stuff. Then I told them pretty much what you said ... and I could hear a "Phew!" from the audience.
-- 73 de JoAnne K9JKM k9jkm@amsat.org
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participants (3)
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Burns Fisher -
David Bartholomew -
JoAnne K9JKM