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