[time-nuts] Disciplining Rubidium

SAIDJACK at aol.com SAIDJACK at aol.com
Fri Apr 25 02:41:52 EDT 2008

Hi Tom,
true, that decision has to be made, and there is probably some cut-off  phase 
difference where the 1PPS position is just reset.
But I would have expected the PRS10 designers to bound the frequency change  
to something less than several parts to the E-10 when the loop time constant 
is  set to 7 hours. Even a frequency error of 1.0E-011 would have drifted the 
1PPS  at a rate of 36ns per hour, so by the 7'th hour it would have been back 
on track  (since I set a 7 hour loop time constant that would have worked well).
I just did not expect such a drastic frequency adjustment from the Rb, and  
would think most people would not mind a slower drift rate while also having  
less of a frequency error. After all the 1PPS was "off course" for a long time  
already anyways - otherwise the error would have been much smaller.
In a message dated 4/24/2008 20:48:04 Pacific Daylight Time,  
tvb at LeapSecond.com writes:

If  you're lucky, the GPSDO gives you an option whereby you
can program your  threshold; your "expectation". But internally
every GPSDO has to make a  decision about when to jump vs.
when to drift. Whether it's hardcoded or  programmable is the

See section 5.1.1 of the Trimble  Thunderbolt manual for a
good example of how this can be  done.


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