[time-nuts] Thunderbolt self-survey results...

Mark Sims holrum at hotmail.com
Sat Aug 30 23:35:19 UTC 2008


Well,  I didn't start out to do a formal test of the survey repeatability.  I was actually testing my ThunderBolt control program.  The survey command causes lots of states in the unit to change and I was actually watching that.  I did write down the results that I got each time (I think I may still have that napkin).  Depending upon the time of day,  a survey could complete (1200 fixes) in from under and hour to over 6 hours.  Before I got my antenna in a better (but still really crappy) location,  the first survey that I did took almost three days!

Lat and lons were spread over around 35 feet,  with most clustered within 12 feet.  Altitudes were spread over 100 feet,  with most clustered within 25 feet.  I plotted the results,  threw out the outliers (usually from those long surveys when the track satellite constellation changed every couple of seconds),  and stuck a pin in the middle of what was left.  

Plugging the result into Google Maps was rather astonishing...  the point on their photo appeared  to be within inches of where the antenna is.
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What was the standard deviation of the dozen surveys?


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