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RE: AO-40 data mode




> One notion I have been thinking about is as follows:
> digitize a wide bandwidth, say 40 kHz with your soundcard.
> Lock onto the beacon to run your AFC loop.  Then you can
> digitize the desired signal without worrying about doppler anymore.
>
> Of course the problem with this scheme is that you can't use
> a standard IF with 3 kHz bandwidth.  You need at least 40 kHz
> with I/Q outputs.

I've been giving this some thought also (ie looking at a software based
solution with an interface at the IF).  You would need enough bandwidth to
cover the entire passband plus whatever Doppler you would anticipate (on the
order of 1 MHz, say).  Tracking the beacon frequency would eliminate manual
Doppler compensation (as you indicated).  This would allow you to select an
appropriate band (up and/or down) within the transponder passband with
reference to the beacon.  I would also consider a DSP solution rather than a
PC.  Although capable of fast operations, this would require a bit more than
what a Pentium can provide (especially if it is running a GUI).

This project would not be for the squeamish, but a working solution would be
much more automated than what is available at present for working the sats,
which in turn would open up the doors to more satellite users (=more
members, =more revenvues, =more satellites, etc).

My 2 cents worth.

Cheers,

George
VE3LQN


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