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 > -- Mark L. Hammond [N8MH] _______________________________________________ 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
