[time-nuts] Common sky pps errors for any GPSDOs?

SAIDJACK at aol.com SAIDJACK at aol.com
Tue Jan 6 00:27:29 EST 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.
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.


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