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[aprssig] Easy Predicting GO-32 for the mobile!

Robert Bruninga bruninga at usna.edu
Fri Oct 12 16:09:34 UTC 2007


I've been trying to come up with an easy GO-32 pass-time
predictor for the mobile.  This morning I got it!  The Ground
track of GO-32 repeats every 10 days!

So All you need on your dash board is this strip of paper.

Day1 Day2 Day3 Day4 Day5 Day6 Day7 Day8 Day9 Day1
---- ---- ---- ---- ---- ---- ---- ---- ---- ----
0930 0910 1025 1005 0940 0920 1040 1015 0950 0930
     1050                1055
2050 2030 2005 2125 2100 2040 2015 2135 2110 2050
     2210 2145                2155

For example, today is Day3 in Wash DC.

If you print these in fixed font, it will show you the pass
times for any day and time zone and location, as long as you
know what day sequence to be on in your area.  And we can have
GO-32 send down a table-of-days in its bulletins!  So if you
ever hear GO32 once, then you will have all you need for
tracking for the next few months or so for your area!

Initially, I assumed this table would be only for Washington DC
(77 deg Longitude) and 40 deg latitude where I calculated it.
But it should also apply anywhere at this longitude north or
south and be off by less than 5 minutes or so. 

Then I thought we would need a different one for every 5 degrees
of longitude... But then realized that just as the pattern
repeats every 10 days in time, it also repeats incrementally in
longitude!  Since the longitude increment of GO-32 is about 26
degrees, that means these multiples of 26 degrees from
Washington DC will have the same pattern on the same day as we
do.  And that every 2.6 degrees in between will have an
additional day offset from ours. 

Wow, it can't get any simpler than that for mobiles to know when
to use their rigs on GO-32 when traveling in wilderness areas.
A similar table could be predicted for ECHO (AO-51) maybe.

ELEVATION ANGLE:  To keep the chart simple, I did not include
max elevations, but that can be added in the final version.  It
is also easy to infer.  The days with double passes are near 30
degrees each (barely detectible by the mobile)  The days midway
between these lowest peak passes are the highest elevations (75
or more degrees).  And you can interpolate inbetween these.

UPLINKS!  The above table gives you only the BEST pass of the
day for your location (passes above 30 degrees).  This is the
pass where you can expecet to receive the GO32 downlink on your
mobile whip antenna.  HOWEVER, every day, there is a pass
exactly 100 minutes before and after each of those passes too.
So now you have 6 chances a day to report your position in the
wilderness and 2 chances a day to receive any APRS message
traffic.

Happy wilderness traveling!
(Oh, and of course, make sure there is someone in your footprint
that is SATgating your data into the APRS system so that your
position and status and any emails get delivered.)...

Bob, WB4APR





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