[amsat-bb] Re: VO-52 Frequency Drift

David Palmer KB5WIA kb5wia at amsat.org
Tue Mar 27 11:45:38 PDT 2012

Nice observations there, John.  I too have noticed frequency drift of
a similar magnitude to what you describe below.  Just about every time
I work a VO-52 pass I need to reset the frequency calibration on
SatPC32 up or down a few hundred Hz.

One thing I thought was interesting from last night's overhead pass
(3/27/2012 around 0320z) was that close to mid-pass, there seemed to
suddenly be a very large amount of noise (almost sounding like hash
from a microwave oven) coming through the passband.  At the time, I
was the only station on the sat, calling CQ with my 0.5 watts, and a
very nice quiet clean downlink.   When the noise came, it virtually
drowned out my input signal, even going up to 5 watts.  The noise
lasted about 30 seconds and then faded out -- it seemed to occupy most
of the passband.  After the noise dissipated, I was surprised that I
had to reset my SatPC32 calibration by about 200 Hz.  I found this
really interesting, the seeming coincidence between the noise and the
frequency offset changing rather suddenly during a pass.  The
graphical plot of the sat path showed it starting the pass just barely
touching the sun line, and ending with the footprint a good ways in --
maybe as the satellite entered more sun exposure its temp increased,
causing the freq shift and possibly a bit of oscillation causing the
noise??   Could just have been me, of course, but it would be
interesting if anyone else has noticed these things.


On Tue, Mar 27, 2012 at 8:41 AM, John Papay <john at papays.com> wrote:
> There were three passes of VO-52 here this morning, 27March2012.
> I was able to copy the beacon on all three passes.  Here are the
> results:
> 1200utc 145862.6
> 1335utc 145861.7
> 1510utc 145861.9
> The frequencies are not exact. My CW offset is 850Hz.  There is
> significant frequency drift and temperature is probably the cause.
> It would be interesting to hear from the control team regarding
> this.
> HO-68 provides an excellent check of your doppler compensation in
> your tracking program.  I find that the beacon is always very strong
> and the frequency is rock solid.  You can save the frequency in your
> program and a month later find that it is right where it was the month
> before.  If you can listen to the beacon with your CW filter on throughout
> the entire pass, you have everything set right, keps, computer clock etc.
> The doppler gets quite severe on a high pass and is a great way to make
> sure you have everything set right.  Since HO-68 is on UHF, everything
> becomes more critical.
> 73,
> John K8YSE

More information about the AMSAT-BB mailing list