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RE: AO-40 KEPS



Thanks Paul. I believe the problem was due to the time increments
I had chosen for the ephemeris steps. It was set to 9 minutes
for AO-40. The az/el columns would display values for the start of 
the interval, but several minutes later I would change to the map
screen which displayed the data for real time which couldn't 
agree with the start of the 9 minute step since several minutes
had passed. My mistake. ........never mind

73
Ken  K5MBV 
__________________________________________________________________

Check the displayed time on the map screen against the time in the 
ephemeris table. Very likely you will find that at a given displayed time, 
the azimuth and elevation values are the same (rounded off in the ephemeris 
table to conserve columns).

If you're running under a recent version of Windows, you might find that 
the displayed time on the map isn't quite right. That will be the case if 
you ever send the map screen (which is forced to be full-screen under most 
video drivers) into the background. Windows has strange ideas about 
timekeeping in this situation, especially Windows 2000. As long as you keep 
InstantTrack on the screen and active, it should keep time correctly (but 
it does depend on DOS or Windows for this function).

If you really find a discrepancy between the azimuth and elevation values 
computed for the same displayed time on different screens of InstantTrack, 
I will be amazed. In that case, please send me all the details. If 
possible, send a screen capture of both screens, plus the elements screen 
for the satellite and for your station, and a copy of your IT.INI file. 
This will give me the best chance of reproducing what you're seeing.

Another possibility is that you have two different satellite entries in 
your InstantTrack database, both named AO-40 for instance, but with 
different object numbers. They would get different keps updates, and thus 
would predict different positions.

If you're trying to match up times second by second during a perigee pass 
(when azimuth and elevation are changing very rapidly), note that the value 
displayed in the ephemeris table is not necessarily the value at the 
beginning of the minute. The exact start time (to 1 second) is displayed on 
the setup screen for the ephemeris display, but the times on the ephemeris 
display are truncated to the minute.

Please help me follow up on this. I don't want there to be any question 
about InstantTrack getting the right answers (on all screens!).

73  -Paul
kb5mu@amsat.org
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