[time-nuts] How does sawtooth compensation work?

Bob Stewart bob at evoria.net
Mon Jul 18 19:25:56 EDT 2016

Hi Nick,

Let's use the example of a Ublox timing receiver.  In the TIM-TP data package, there is a qErr value, which is the quantization error of the *next* PPS pulse output by the receiver.  At the next PPS, you would subtract that from the unwrapped phase measurement your GPSDO makes and that would give you the actual phase difference between your OCXO (or generated PPS) and what Tom has called "The PPS", which is the pulse occurring exactly at the top of the second --- give or take coax length, etc.


      From: Nick Sayer via time-nuts <time-nuts at febo.com>
 To: Chris Arnold via time-nuts <time-nuts at febo.com> 
 Sent: Monday, July 18, 2016 5:31 PM
 Subject: [time-nuts] How does sawtooth compensation work?
I've read Tom's page about sawtooth PPS jitter and I believe I understand where it comes from.    My current GPSDOs ignore the phenomenon. Certainly at the moment, I'm satisfied with that.  The systems gravitate towards PLL time constants that average it all away. 

What I'd like to understand is how sawtooth compensation works with receivers that support it. Is it that I expect an NMEA sentence with a nanosecond offset value that I add to any phase difference observation that I get?

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