[time-nuts] How does sawtooth compensation work?

Bob Stewart bob at evoria.net
Tue Jul 19 00:30:52 EDT 2016

The LEA-6T is a good receiver, but it does have a sawtooth bug.  From time to time, when the sawtooth is approximately 10,299 (or is it 10,399?) ps, the sign of the sawtooth is wrong.  It's an easy fix:  Just check whether the sawtooth makes "this" corrected measurement worse than the previous corrected measurement.  I haven't checked the LEA-M8T for the bug, as I turned off the notice message when I corrected it.

Bob -----------------------------------------------------------------


      From: Mark Sims <holrum at hotmail.com>
 To: "time-nuts at febo.com" <time-nuts at febo.com> 
 Sent: Monday, July 18, 2016 10:28 PM
 Subject: [time-nuts] How does sawtooth compensation work?
Or use the sawtooth compensation value  to control an external variable delay line circuit to move around the PPS signal from the receiver.  This can get interesting to implement if the receiver can output negative values for the sawtooth compensation (hint: add a bias to  the sawtooth value to make the compensation values always positive and adjust the antenna cable delay command to remove the bias value that you add.  Oh, and for some receivers you have to reverse the meaning of positive and negative sawtooth corrections and/or cable delay values).  It is even more interesting if the receiver outputs the sawtooth correction after the pulse it just generated... hint: get a different GPS receiver).

> A device that uses the sawtooth data shoves it into the control loop along with the measured early / late information on the PPS. 

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