[amsat-bb] Re: SatPC32 Help Needed

David Palmer dave at zdap.com
Wed Oct 6 13:11:50 PDT 2010

Hi Ed,

Thanks for the fast response!  Yeah, both the original poster (Guy)
and myself are using computer tuning of both radios.  I know for sure
my SatPC32 is set up for adjusting both the uplink and the downlink,
and I see the readout on the radio changing accordingly, so it seems
to be working ... what puzzles me is why the computer tuning seems to
be so poor, since even though it's complex math, it's just math and
the computer should be able to keep up!

Of course, since there are many on the list here using SatPC32 and
twin radios successfully, I'm almost certain it's operator error
that's causing this slight drift (or lack of complete correction), but
I just can't figure out what it is yet.  :-)

One thing I *did* notice with the Twin FT-817's, is that those radios
(817,857, 897) do not update the TX frequency by CAT while they're
transmitting ... so as I call CQ, I definitely hear my voice drop in
pitch because the SatPC32 is busy updating the downlink frequency but
the radio is busy so is not updating the uplink frequency.  I accept
that as normal (and just unkey to let the computer reset the radio for
proper shift) but ...

... what's confusing me is that the amount of correction seems to
change from pass to pass and even during the pass ... at first (out of
the box) SatPC32 was about 2400 Hz low on the uplink based on the
values in the doppler.sqf file.  I just figured it could be due to
radio calibration, etc, so I applied the calibration factor, and now
it's much closer ... but still I seem to have to adjust +/- 100 to 200
Hz at the start of the pass, and periodically during the pass, to keep
my return pitch constant.

Thanks everyone!

Dave KB5WIA CM88 Northern California.

> When one gets up to modes like LS, it gets more challenging because both
> Doppler and rate of Doppler change are greater.  Probably should consider
> computer tuning of the radio at this point.

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