[aprssig] Balloon - lessons learned (AVMAP-GPS) - GreenLight Labs GPS?

Robert Bruninga bruninga at usna.edu
Mon Apr 7 11:24:48 CDT 2014


See web page for summary of the balloon mission:
http://aprs.org/balloons.html



APRS Lessons Learned: -- What the  GPS map shows MAY NOT BE what your radio
knows.



We were running a GreenLight Labs GPS on the D710:
http://www.greenlightlabs.com/gps-710/



For the chase, we added an AVMAP GPS for the map display and plugged it
into the "pass-through" socket on the Green light labs GPS.  Everything
seemed to be working.



20/20 HINDSIGHT HINTS:  Occasionally we notice the D710 was not updating
and so we cycled power and continued.  Some times the AVMAP was not
updating.  Sometimes when the AVMAP was plugged into the Green Light Labs
GPS, then the D710 did not get GPS updates.  But generally, a power cycle
fixed it.  Did it maybe 3 times during the all day chase.



PROBLEM:  What screwed us up was "assuming" that the balloon ICON SHOWING
on the AVMAP GPS was the same last-updated balloon data showing on the
Kenwood D710.  So we were visually driving and chasing the BALLOON ICON on
the AVMAP not realizing that it was the 2nd from last actual position data
heard.  But each time we LOOKED at  the data on the kenwwod we WERE seeing
the last known position (looking mostly to see the altitude).  But you see,
they were not the same.  Apparently the last two packets did not make it to
the AVMAP.  So we were searching based on the time and altitiude on the
radio and the visual map data on the AVMAP, not realizing they were
different.



Finally when I happened to compare LAT/LONG numbers on the radio, to our
searching area, it was 7 miles to the east!



And searching through the 150+ AVMAP APRS entries provided nothing to
correlate the two.  (it shows no lat/long and the altitude it shows is the
LAND elevation, not the balloon!)  And since I was completely trusting the
balloon ICON on the GPS map display, I never noticed that the distance and
bearing on the Radio was showing it 7 miles away.



20/20 Hindsight.  Always use the final data in the RADIO as the last known
information.  It has to be right.  There may have been a transmission error
between the radio and the GPS display.



WB4APR, Bob
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