[aprssig] Trackers from Heaven?

mconner at aer.com mconner at aer.com
Tue Jul 31 15:07:23 EDT 2007

Robert Bruninga wrote:
> 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.

Sounds about right for battery life, could be less.  The balloon reaches burst altitude in under two hours and would not need to transmit after that.

> 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..


Total is 60-some every 12 hours in the CONUS, plus a handful at odd times to support severe weather forecasting, rocket launches, experiments, etc.

> 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.

Indeed, further processing is required on the ground to derive position and velocities.

> 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..

I'm a little surprised that these were in the 400-406 MHz band.  All the operational sites I know of are using 1680-ish MHz even for non-GPS sondes.  The site at Sterling VA does testing/evaluation of NWS upper-air stuff, so maybe it came from there.

Is this what it looked like?

> 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...

Your nearest site would be the Sterling VA office near Dulles Int'l.  
Launch times are about one hour prior to the nominal 1200 and 0000 UTC, or at 0700/1900 EDT.

You could also go to Wallops VA, but you'd probably need to bring a boat with you for the chase.

73 de Mark N9XTN

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