[amsat-bb] Re: PC clock

Mark L. Hammond marklhammond at gmail.com
Tue May 11 13:25:38 PDT 2010

Hello Domenico,

The very excellent SatPC32 program "leads" so as to keep an accurate
pointing at a satellite.  It has several adjustments for how often the
rotors are updated, gain consideration of the antennas in use, etc.


Mark N8MH

On Tue, May 11, 2010 at 4:07 PM, i8cvs <domenico.i8cvs at tin.it> wrote:
> ----- 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
> overhead.
> 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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Mark L. Hammond [N8MH]

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