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Re: Satellite Inquiry



Emily,
I made this point knowing that accruracy includes time, Kep's, station
coordinates, and rate of tunning, besides tunning increments. As the Doppler
shift becomes greater the amount of error becomes greater, and at some point
it makes the signal unusable. Time can be corrected , but kep's are not that
easy and as you pointed out the shift is not linear,  but peaks at the TCA.
This is where time and kep's are of greatest importance. When you are
correcting 60,000 to 100 that is only allows for a  0.2 % error.

Art
----- Original Message -----
From: "Emily Clarke" <w0eec@amsat.org>
To: "KC6UQH" <kc6uqh@cox.net>
Cc: "AMSAT BBS" <amsat-bb@amsat.org>
Sent: Tuesday, February 22, 2005 7:22 AM
Subject: Re: [amsat-bb] Satellite Inquiry


> 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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