[time-nuts] GPS antenna length correction

Brian Lloyd brian at lloyd.com
Tue Apr 29 09:27:32 EDT 2014


I want to thank everyone for their answers. I was sure I had the geometry
right and that the additional latency would make the position "fuzzier"
because I kept thinking that the clock was absolutely correct.

Of course, the clock in the GPS receiver converges on a time that is offset
from absolute time by the delay in the cable. This time offset is equal and
opposite to the extra path length for each satellite's range, thus ensuring
that the position calculation is independent of connecting cable length. So
this corrects for the (apparent) path length error but still leaves a clock
offset error which is then corrected by the cable length input value.

I get it now. Thank you all very much. This is something that has bothered
me for some time and finally seeing the solution makes me feel a lot better
about GPS installations in aircraft.

-- 
Brian Lloyd, WB6RQN/J79BPL
706 Flightline Drive
Spring Branch, TX 78070
brian at lloyd.com
+1.916.877.5067


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