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 [email protected] 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: [email protected] [mailto:[email protected]] 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 _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb