Bob, > On the sub-set of receivers that send you the sawtooth correction *after* (as > in 200 ms after) the PPS
Right. The 1PPS delay line method is not compatible with these chips. > If the sawtooth says the edge was late, you can never get it back to correct > (accurate). The systems that use 1PPS delay chips solve your worry with an at-power-on adjustment to the receiver's antenna delay parameter. So if you have a 256 ns 8-bit programmable silicon delay line, instead of telling your receiver that your antenna delay is X you tell it X - 128 ns. Then the delay chip acts like a -128 ns to +127 ns phase stepper instead of a 0 to 255 ns phase stepper. /tvb ----- Original Message ----- From: "Bob Camp" <kb...@n1k.org> To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com> Sent: Tuesday, July 19, 2016 4:06 AM Subject: Re: [time-nuts] How does sawtooth compensation work? Hi 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. Bob > On Jul 18, 2016, at 11:28 PM, Mark Sims <hol...@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. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
