[time-nuts] pps vs. 10 MHz timing

[SAIDJACK at aol.com]

Hi Magnus,
 
on our Fury system the phase relationship between the 1PPS (clean OCXO  
version) and the 10MHz is established during power-on, then held stable (it is  
generated by the same 10MHz crystal) unless it for some reason drifts more  than 
+/-220ns away from UTC at which point it is reset to UTC, or until it is  
changed by user-command.
 
We do also have the raw GPS 1PPS available (jumper selection option) which  
is asynchronous to the 10MHz, and as you mentioned will drift since it is  
generated by a separate crystal, and clocking system.
 
One could use two or three cascaded FF's two avoid the  
setup/hold/metastability issues, then set the phase via software command so as  to compensate for 
the FF-induced phase delays.
 
You are right, there are so many ways to cross that river :)
 
bye,
Said
 
 
In a message dated 12/12/2008 15:16:00 Pacific Standard Time,  
magnus at rubidium.dyndns.org writes:

You  really can't sync up some PPSes to the 10 MHz by simple DFFs since 
the  variations may be more than 100 ns during some phases of the 
training and  holdover shifts. The PPS output should always be generated 
using the 10  MHz such as they have a stable phase-relationship. The 
generated PPS is  then compared to the source PPS and controlled phase 
adjustments should be  done.

Cheers,
Magnus