Re: [amsat-bb] Satellite Inquiry

[Emily Clarke <w0eec@xxxxxxxxx>]

At 10:57 PM 2/21/2005 -0800, you wrote:
>The other question is with a +/- 60 KHz of Doppler shift and +/- 100 HZ for
>SSB copy is it reasonable to expect computer correction of this magnitude?

The Icom 910 will step in 1 Hz increments, though I've set the computer to 
step it when the Doppler changes 10 Hz (which looks like 10 Hz 
increments.)  This cuts down on overhead on the CI-V bus and doesn't result 
in conflicts when I manually tune the radio.  I feel this is 
quite  reasonable for voice, CW and PSK copy provided everyone is using 
Full Doppler Tuning, better known as the 1 True Rule [ note to Rick and 
Paul - yes, I'm a convert :-) ]

Not everyone is using FDT on modes V/U and V/S and it isn't really required 
for FM in those modes.  However, modes U/S, L/S or U/V (mode B) require it 
even for an FM satellite.  In U/V FM, a center tuned transmitter would be 
outside the FM capture range of the satellite's receiver for much of the 
pass and could cause harmful interference, something I observed when the 
ISS was in Mode U/V voice.

[ Assuming a 70cm FM uplink into a 6KHz wide (+/- 3 KHz) capture range 
receiver and an 18KHz doppler shift over the life of the pass, the 
center-tuned transmitter would be "off-frequency" and out of capture range 
for something like 66% of the pass - moreso if you consider that time-wise 
the doppler shifts are non-linear over the life of the pass and shifts the 
most at TCA.]

73,

Emily


---------------------------------
W0EEC - CM87tm
AMSAT Area Coordinator - San Francisco Bay Area
http://www.projectoscar.net    http://www.PlanetEmily.com

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