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tracking through APRS



Hi there,

I'm a total newbie when it comes to satellites so please forgive my
ignorance and use of the incorrect terminology.

I was wondering if someone could give me some feedback about the
following:

I'm writing some APRS software for a Linux platform which transmits
satellite objects. I think Bob Bruninga wrote something similar for DOS
and I will check that out soon too. These objects will display the next
AOS for a given satellite and its current position when the satellite is
out of sight (below the horizon). They will be transmitted about every
15 min or so (user defined). As soon as it gets in sight it will step up
the tx rate to say once a minute (also user defined). Then the object
will display its current position plus the elevation and azimuth.

The purpose of this is to give people a live feed of where the
satellites are and where to point their antennas to if they are within
a 30 miles radius of the transmitting station. Perhaps this can help
people out in the field (or on events like the field day or JOTA)
tracking the satellites on their D7 or other APRS capability.

Now to my question. If I would broadcast the elevation and azimuth data
for the position of the transmitting station, would this still be
accurate enough for say a 30 miles radius? I realize it will not be
exact, but will it still be useful?

I tried to get an answer using tracking software. What I did is I
compared the data of a predicted pass at the transmitter's location and
at 4 points 30 miles away from the station. I picked the point during
the pass at which the elevation angle would be the largest for that pass
at those positions. This is the data I obtained:

location:   El:   Az:  time:

@tx loc.    77    55   10:13:53z
30mi NW     76    54   10:13:48z
30mi SW     72    50   10:13:56z
30mi SE     78    56   10:13:44z
30mi NE     80    59   10:13:57z

To me this seems close enough to be useful, but I wonder if that
assessment is correct.

Any feedback is appreciated.

73s,
Alex
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