[time-nuts] Performance of the Thunderbolt self-survey / antennas

Mark Sims holrum at hotmail.com
Mon Jul 13 04:39:48 UTC 2009


Now that I have a precise spot (+/- 4cm) known on my front deck I set up a tripod and did numerous 1400 point self-surveys with a Thunderbolt.  This spot is surrounded by very tall trees and multipath from the trees,  steel gates and stucco walls,  a house,  an iron fence, etc.  I used four different antennas:

1) A Sokkia geodetic grade L1/L2 antenna
2) A Aero survey grade L1 only antenna
3) A Datum timing antenna
4) A cheap patch antenna

I could not find any repeatable differences in the performance of any of the antennas.  The $3000+ geodetic grade antenna performed no better than the cheap $5 dollar patch antenna.

Composite performance over 22 runs was:
Avg lat error: 1.4 feet,  std dev 4.48 feet
Avg lon error: 2.24 feet,  std dev 2.87 feet
Avg alt error: 6.00 feet,  std dev 15 feet

Although I did not do any extended timing tests between the antennas,  the numbers that I did see make me suspect that timing performance among the antennas would be similar.  A couple of 24 hour runs between the cheap patch and the geodetic antenna were the same.  A cheapskate could probably get excellent results by mounting a cheap patch antenna in the middle of a large pizza pan ground plane.


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