[time-nuts] GNSS antenna delays
Michael Wouters
michaeljwouters at gmail.com
Wed Jun 29 17:46:55 EDT 2016
The discussion about antenna cable delays made me think of the issue of the
antenna delay. An antenna typically has a bandpass filter and amplifier so
there clearly is some non-negligible delay associated with this.
The issue is usually sidestepped by calibrating the delay of
receiver+antenna (against what? A calibrated receiver + antenna from
the BIPM of course...)
But sometimes, after calibration, an antenna in the field has to be
replaced with a different antenna and the original calibration is
invalidated. It then becomes necessary to expand the uncertainty of the
delay.
I did read a NIST paper where they described measuring the delay by
physically disassembling the antenna so that they could feed signals
directly to the electronics. Delays like 30 ns were measured, I think.
Myself, when changing antennas I have seen steps like 10 ns.
Does anyone have any data points to add to this ?
Cheers
Michael
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