Philip you might have a typo here:
You say, for SO-50, "from AOS I lower my receive frequency (and continue lowering it as the bird approaches LOS." You do lower the frequency through the pass, but you actually start by raising the frequency, then you lower. So with AO-91 you start by lowering the frequency and then raise it through the pass.
73, John Brier KG4AKV
On Wed, Jun 5, 2019, 13:56 Paul Stoetzer via AMSAT-BB amsat-bb@amsat.org wrote:
When you're on the ground listening to SO-50 as it approaches you, the RF waves are compressed, and thus the frequency you receive at is higher than the frequency the satellite is transmitting at.
When you're transmitting to AO-91 as it approaches you, you need to compensate for the fact that your RF waves are going to be compressed and appear at the satellite at a higher frequency than you are transmitting at. So you have to transmit lower than the nominal frequency.
73,
Paul, N8HM
On Wed, Jun 5, 2019 at 1:45 PM Philip Jenkins via AMSAT-BB amsat-bb@amsat.org wrote:
This came up at AMSAT Academy at Hamvention, and I still can't wrap my
head
around it (something simple I'm not getting, I'm sure). I know the xmit/receive frequencies aren't shifted, stay the same at the satellite.
SO-50 has a 435 Mhz downlink; as the satellite approaches me from AOS I lower my receive frequency (and continue lowering it as the bird
approaches
LOS). So far so good.
AO 91/92 have a 435 Mhz uplink,; as the satellite approaches me from
AOS, I
go up in my transmit frequency.
Here is where I get lost: Why do I* lower* the frequency on 435 Mhz when receiving a satellite, but *raise* the 435 Mhz frequency when
transmitting
to a satelllite?
So, my question boils down to - why should transmit doppler shift go in
the
opposite direction from receive on the same band? In both cases, the satellites are approaching me (from AOS).
Basically, why the difference when I'm transmitting and when I'm receiving?
73
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Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: https://www.amsat.org/mailman/listinfo/amsat-bb