[time-nuts] How does sawtooth compensation work?
kb8tq at n1k.org
Tue Jul 19 07:06:43 EDT 2016
On the sub-set of receivers that send you the sawtooth correction *after* (as in 200 ms after) the PPS …. the delay
line correction thing does not work very well. Also in a “strict time nuts” sense, you can only delay the edge. If the
sawtooth says the edge was late, you can never get it back to correct (accurate). Not at all a big deal for a GPSDO.
It is a big deal if you are looking for a “perfect tick” time wise.
> On Jul 18, 2016, at 11:28 PM, Mark Sims <holrum at hotmail.com> wrote:
> 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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