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[aprssig] Trackers from Heaven?

Robert Bruninga bruninga at usna.edu
Mon Jul 30 18:35:37 UTC 2007


Someone just walked into my office with a NWS Radiosonde they
found in a field.  Talk about TRACKERS from HEAVEN...

The sign on the side says what it is and that it is of NO
FURTHER USE.  So therefore its now his.  We opened it up and
noticed a GPS patch antenna and on the other side of the board
was a pair of GPS chips in 1.2" square cans.  Also there was
anotehr can for the RF transmitter and a 4 position dip switch
and a frequency table.

We hooked up a 9v power supply across the dead battery and it
sprang to life.  Could just barely see it on a spectrum
analyzer.  RF power output is probably about 10 milliwatts or
less.  Looked up the battery and it appears the battery life is
designed for about 6 hours.

200 of these are launched every day at 0000 and 1200 UTC by the
WX service and they all fall into someone's backyard every
day...  Using HT Dfing techniques, it should be easy to find
these things before the 6 hours is up..

Of course the telemetry format is not APRS, in fact, I think the
GPS chip set only recovers GPS doppler rates and sends those to
the ground for further processing???  but it would be fun for
someone to write  a decoder.  Then all we have to do is HACK the
RF oscillator to get it onto a HAM band and we have a continuous
source of GPS trackers for throw-away events.

I didn't have time to take photos, before the person had to
leave, but having had so much fun chasing the APRS balloon last
week, I now realize that you can chase balloons every day if you
simply tune to one of the frequenceis below, about 3 hours after
the NWS launches them at the same time every day..

400.250
400.625
401.000
401.375
401.750
402.125
402.500
402.875
403.250
403.625
404.000
404.375
404.750
405.125
405.500
405.875

Lets see, 1200 and 0000 UTC is 8 AM and PM, and about perfect
for a quick ballooon chase.  Now to find out our local launch
site...

Bob, Wb4APR





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