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[aprssig] Trackers from Heaven?

Scott Miller scott at opentrac.org
Mon Jul 30 23:05:14 UTC 2007


I got to launch one of these once.  I was under the impression that they 
were AGPS and would require signal processing on the ground to get 
position and velocity data.

Around here they send them up every hour for at least part of the day 
prior to a rocket launch.  When they've got one on the pad that keeps 
getting scrubbed, that adds up to a lot of radiosondes over a week or 
two.  Not sure where they all wind up, though.  Out of boredom one night 
(my job involved babysitting the file transfer system) I started trying 
to run the files through a balloon prediction program.  Didn't ever 
quite get the format right, though.

Scott
N1VG

Robert Bruninga wrote:
> 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.





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