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Re: Doppler

At 2:08 PM -0400 6/17/06, ANTHONY JAPHA wrote:
>Also, IT seems to give doppler for the beacons but not for the
>transponders.  Is that correct?

Yes, for the on-screen displayed Doppler.

>   Seems unusually not useful.

The beacon frequency is usually either the center or just off the end 
of the range of transponder downlink frequencies. Since the 
transponder bandwidth is a tiny fraction of the transponder 
frequency, any difference in Doppler shift between the beacon and the 
downlink is similarly tiny. The difference is negligible when you're 
manually tuning from an on-screen display.

In the case where the beacon frequency is NOT nearly identical to the 
downlink frequency, you are free to set InstantTrack's "beacon" 
frequency to the center of the downlink passband. There's no 
particular need for InstantTrack's idea of the "beacon" frequency to 
be the actual beacon frequency.

And if you'd prefer that InstantTrack display the NET Doppler 
(downlink shift minus uplink shift) for use with an inverting 
transponder, you can give InstantTrack a "beacon" frequency 
corresponding to the frequency difference.

That's all for the on-screen display. For automation, the case is 
different. InstantTrack's interface with a radio driver for automatic 
tuning is frequency-independent. The radio driver is free to compute 
Doppler shift for the actual frequencies in use.

73  -Paul
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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