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[aprssig] Suggestion for APRS over Satellite

Robert Bruninga bruninga at usna.edu
Tue Apr 22 14:33:27 UTC 2008


> ...the idea of building some equipment for 
> extreme remote telemetry stuff to be done 
> over satellite.  (Similar to Bob's 
> [buoys and] project in Mongolia). 
> 
> ... extremely useful [to]... include its current 
> orbital data in the beacon packet... [so that the
> instrument]... could power down its radio until the 
> next useful satellite pass.  

Yes, APRS even has a format for it that we have used in the
past.  We have a two-line format and a one-line format.  But for
many satellites it is not necessary.  Remember, we have had
amateur satellites for 40 years, but only personal PC's for
maybe 20.  We can estimate pass times very simply.

The most popular HAM satellite you can use from your FM mobile
is AO-51 and it comes over 6 times a day, and the patter repeats
every 5 days.  But you only need one pass a day to be able to
predict the others, and since the pattern repeats every 5 days,
you only need 5 times (20 bytes) to allow good predictions for
many weeks.  See the info on about 50% down this page:

http://www.ew.usna.edu/~bruninga/sset.html

Of course, these timer/per day have to be predicted for one
location.  They are different at other locations.  But for fixed
sensors, then, a single packet for that location would do.

Just post those 5 times on your dashboard, and while commuting,
you can watch out for those passes any day for a few months.
Before updating those 5 numbers.  For GO-32 which supports APRS,
the repeat-time is 9 days.

Bob, WB4APR





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