[time-nuts] Common sky pps errors for any GPSDOs?
SAIDJACK at aol.com
SAIDJACK at aol.com
Tue Jan 6 05:27:29 UTC 2009
Hi Matt,
having 140ps matching of the 1PPS between units is the equivalent of knowing
your antenna position to within ~0.14 feet total error max.
Thats less than one inch error per antenna!
That would require some serious antenna surveying :) This accuracy is
impossible to achieve with timing GPS receivers without
carrier-phase/post-processing as far as I know.
If you are only looking at second-to-second jitter of less than 140ps then
we can do this without a problem.
Our ADEV at 1s measurement intervalls on the Fury OCXO is about 2E-012, or
2ps. So the pulse to pulse jitter would be much more than an order of
magnitude better than you require.
On the Fury GPSDO one could get better than ~5ns unit to unit variation rms
with proper antenna surveying, and calibration of the 1PPS output in 1ns
steps using the 1PPS shift commands.
bye,
Said
In a message dated 1/5/2009 18:22:01 Pacific Standard Time,
boyscout at gmail.com writes:
But Said just told us that he sees about 25ns difference between
units, which is about 180 times worse than 140 ps.
In VLBI I think that they can deal with an unknown phase error between
the two LOs as long as that phase error remains relatively constant
over the period of integration. That is why they care about ADEV.
They just correlate the two signals, and subtract out that constant
phase error. My problem is that we can't just do that in this
application. We need to know that phase error a priori.
Matt
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