[amsat-bb] Re: ARISSat telemetry and Doppler tuning

[Mark L. Hammond]

Ron,

Alan's points are spot on.  That being said---I see something similar to
what you are seeing and "blame" the Keps :)

In the first few days, the manual freq. correction at TCA was over 1,000Hz
(seems like I had to shift it down, so -1,000) as compared to AOS and
LOS...which were "on frequency."

It has gotten much better over time.  It was off -500Hz, and now it's under
-100Hz at TCA--so my thought is that the Kep elements are to blame, not a
drifting satellite transmitter, etc.

73!

Mark N8MH

On Thu, Aug 18, 2011 at 9:59 AM, Alan P. Biddle <APBIDDLE at united.net> wrote:

> Ron,
>
> That behavior is common around TCA, Time of Closest Approach.  At that time
> everything is changing rapidly, and slight errors in QTH position, system
> clock, and Keps can be magnified.  I have seen a few hundred Hz shift at
> that time with new satellites whose Keps have not fully converged.  The
> same
> if the system clock is off a bit.  As you probably know, the basic Windows
> internet time calibration facility can be tweaked, but it is better to
> replace it with one such as Meinberg.  Finally, always have the latest
> Keps.
> Updating with SATPC32 is easy and only takes a few seconds.
>
> It is unlikely to be a factor on 2 meters, with a fast computer, but you
> can
> try increasing the update calculations in SATPC32.  Look on the CAT page.
> You will see tick boxes for 1X, 5X and 10X.  Try 5X and see if it makes any
> difference.  Note that this setting is not sticky.
>
> Actually, your results show you have just about everything nailed.
>
> 73s,
>
> Alan
> WA4SCA
>
>
>
> -----Original Message-----
> From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
> Behalf Of Ronald G. Parsons
> Sent: Thursday, August 18, 2011 8:35 AM
> To: AMSAT-BB
> Subject: [amsat-bb] ARISSat telemetry and Doppler tuning
>
> Last evening, after having several days experience capturing ARISSat
> telemetry, I sat at my radio and watched carefully how SatPC32 and
> ARISSatTLM played together. I had settled on a tuning correction value of
> -540 HZ to get the CW signal to center around the CW tuning point as the
> Doppler correction was handled by SatPC32.
>
> The approach of the satellite seemed normal. but as the satellite passed
> by,
> I noticed the CW signal average "position" to be creeping upward, needing a
> reduction of the tuning correction by about 40 Hz to -500 Hz. This lasted
> for a couple minutes and then the CW signal started creeping down and I had
> to go back to my -540 Hz value.
>
> The first explanation I could think of is that the Doppler correction
> computed by SatPC32 from my position and the keps was in error. But of
> course, it could have been a change in my radio (unlikely as it had been on
> for hours) or a change in the frequency of the CW signal from the
> satellite.
>
> I'll keep watching this and wonder if others have noticed something
> similar.
>
> Ron W5RKN
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-- 
Mark L. Hammond [N8MH]