[time-nuts] Some results of PRS10 and Trimble Resolution

Hal Murray hmurray at suespammers.org
Tue Jun 27 14:49:33 EDT 2006

> If you feed a PRS10 with a 1PPS that has systematic jitter (NB: not
> random jitter!) like the Oncore GPS receivers have, then some heavy
> duty averaging is called for before the loop is fed.

> Unfortunately the 1/256'th exponential filter provided in the PRS10 is
> not long enough to fill this need.

> Newer versions of the PRS10 firmware allows you to set the PPS input
> offset, and with a small program you can transmit the negative
> sawtooth correction from the GPS to the PRS and that solved the
> problem for me.

Where is the sawtooth coming from?

My first guess was some sort of beat between the Oncore crystal and GPS, but 
that would probably be temperature dependent and hence unlikely to show up as 
a specific frequency.

Is it something deliberate?  Maybe it's trying to avoid the dead zone in a 
phase detector?

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