[time-nuts] Synchronisation using GPS

[Robert Lutwak]

If the two positions are fixed, say a permanent VLBI or bi-static radar 
installation, You can do pretty well (say < 5 ns delta between sites) with 
GPS-steered cesium.   The long-term stability of the delta can be even 
better (say < 1 ns).  Even with civilian one-way GPS, the cesium allows you 
to average the position/time with averaging times of days.  Once locked, you 
have the short-term stability and phase noise performance of a good cesium, 
with long-term phase and frequency accuracy driven by the GPS constellation.

Historically, there have been several off-the-shelf GPS-steered-cesium 
solutions, there was an option board for the TrueTime XL-DC, which steered 
the 5071A, and the Datum 6801, which steered the FTS 4040/CsIII series. 
There was even a short-lived product, the Datum Cs+, which crammed it all 
into one box.  Alas, all of these products are out of production, but you 
may find them on the used market.

-RL

------------------------------------------------------------
Robert Lutwak, Senior Scientist
Symmetricom - Technology Realization Center
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