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Bob Bruninga <bruninga@usna.edu> wrote:

>I made an error in my newbee excitement...

Not to worry: excitement is good. Gets people thinking.

Another approach I've thought of: the Doppler of an LEO
satellite is significant, and must be accounted for. Rather
than a 3 kHz passband HF radio, or even a 1 kHz wide Warbler,
why not make a radio that's wide enough to accomodate the
Doppler without tuning?

Convert to I/Q baseband and do all subsequent processing
(including Doppler tracking) in software. At 70cm the
Doppler is +/- 10 kHz, so make the radio have an IF
response from as low as you can go to 12 kHz. You can't
quite go to DC, but you can get close. The upper limit is
set by the audio hardware, but most of the CODEC chips
used on sound cards and DSP eval boards max out at 48 ksps,
leaving plenty of room for a 12 kHz signal.

Since the radio frequency is fixed, all you need is one
crystal. It won't be an off the shelf crystal, but you
only need one.

Laura Halliday VE7LDH     "Que les nuages soient notre
Grid: CN89mg                     pied a terre..."
ICBM: 49 15.042 N 122 59.053 W       - Hospital/Shafte
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