[amsat-bb] Re: PC clock

i8cvs domenico.i8cvs at tin.it
Tue May 11 13:07:22 PDT 2010

----- Original Message -----
From: "Greg D." <ko6th_greg at hotmail.com>
To: <w7in at montana.com>
Cc: <amsat-bb at amsat.org>
Sent: Tuesday, May 11, 2010 7:47 AM
Subject: [amsat-bb] Re: PC clock
> Hi Larry,
> Ok, I understand the need for an accurate clock, though I believe you're
> expectations for being able to track an overhead pass is pushing the
> limits of orbital prediction pretty hard.  Another ham I know locally
> tried this, and  ultimately gave up.  His issue was not one of clock
> accuracy, but of Keps and the mathematics behind them.
> Greg  KO6TH
Hi Greg, KO6TH

When the software calculate the Az and the El of the satellite at the right
time with an accurate clock then it send a command to the rotators but the
antennas takes a certain time to go in that calculated position and when the
antennas are finally there then the satellite is already in another position
far advanced in it's orbital path particularly when the satellite pass is

I dont think you want to run the motors every 5 or 10 seconds othervise your
control relays will work as a machine-gun

So the issue is not on clock accuracy or Keps or mathematics behind them but
it is on the tracking system that we normally use to mimichaise the
satellite position with a phase difference between the satellite calculated
position and the actual antenna position when the traching command is sent
to the motors.

If you go over the roof and you follow the ISS by naked eye you will realize
that your antenna pointing is always a little bit behind the ISS position in
the sky and so a very accurate clock to track a LEO satellite is meaning
less particularly using high gain antennas with a narrow main lobe.

73" de

i8CVS Domenico

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