[time-nuts] TBolt-PRS10

[Charles P. Steinmetz]

Juerg wrote:

>Having a M12+Timing GPS driving the 1 Hz input of my PRS10. I decided
>to upgrade my house referenc switching to a Tbolt as the 1 Hz source.
>    *   *   *
>Tests showed maximum deviation of 2 nsec with the Tbolt over 1000
>seconds
>    *   *   *
>Here are my questions:
>Are 2 nsec acceptable for a Tbolt

2 nS maximum deviation over 1000 seconds is good for a Tbolt, in my 
experience.  You apparently have a good, strong signal from the 
satellites, low multipath, and an accurately surveyed antenna location.

>What should the Tbolt loop time be for this application

That depends on a number of factors, primarily (i) the 
carrier-to-noise ratio you have (satellite signal strength) and (ii) 
the stability of the OCXO in your particular Tbolt.  Basically, you 
want the OXCO to dominate up until it enters the random-walk 
phase.  The best TC will probably be between 250 and 800 seconds to 
achieve this, in my experience.  If the Tbolt goes into holdover from 
time to time, you may need to compromise between best absolute 
performance and holdover recovery.

>What should the loop time be for the PRS10

The PRS10 manual addresses choosing setup parameters for disciplining 
the unit with the 1pps of a GPSDO.

>What is the long term performance of the Tbolt and what is the
>contribution due to the GPS signal.

Generally, you can expect parts in 10^-13 at 10k seconds, dominated 
by the GPS deviation.  If you have poor carrier-to-noise, somewhat worse.

>What is the resolution of the Tbolt detecting and correcting the 1 pps
>and is it done by changing the OCXO frequency for short periods.

Yes, the 1pps is corrected by adjusting the OCXO.  You can set the 
maximum allowed frequency error with TboltMON or Lady Heather (of 
course, if you set it too tight it will take forever to stabilize 
coming out of holdover).  The Tbolt can also be set to slip cycles 
during recovery ("jam synch") to speed up the process.  I don't think 
the adjustment resolution is an issue -- it is much smaller than the 
pps jitter.

You will be using a VERY slow loop in the PRS-10, so jitter in the 
GPSDO 1pps will not be much of a factor.  The pps deviation at very 
long time scales (tens of hours and up) is what matters.

Best regards,

Charles