> Le 14 août 2018 à 09:29, Mike Cook <[email protected]> a écrit : > > Sorry about the previous blank mail. Finger jitter. > > > >> Le 14 août 2018 à 04:29, Chris Caudle <[email protected]> a écrit : >> >> On Mon, August 13, 2018 9:16 pm, Chris Burford wrote: >>> I have a (generic?) GPSDO which contains an Oscilloquartz STAR 4+ OCXO >>> that I am using to steer a PRS10 RFS. I'm a little confused on where the >>> 1PPS is coming from with respect to the GPSDO. > > As Chris points out the 1PPS from a GPSDO will « generally » be derived from > the primary frequency and can show better performance than directly from a > GPS receiver. > However this is becoming less and less true. > If you look at the Oscilloquarz blurb for the Star 4+ ( I found some here > <http://pdf.directindustry.com/pdf/oscilloquartz-sa/star3-4/62169-330779.html#search-en-oscilloquartz-star-4> > ) , you will see that the phase stability (jitter) on the 1PPS output is +/- > 30ns when locked to GPS, an it has a timing grade GPS receiver. This is not > as good as other GPS modules now. 15ns is normal, with some less than half > that. > The PRS10 has outstanding PLL control already. The SRS product doc gives +/- > 10ns accuracy with +/-1ns resolution. > I don’t think that you are buying much with disciplining the PRS10 with a > GPSDO 1PPS. Do you have any TIC measurements in this config to compare with a > direct GPS 1PPS feed? >
I forgot to mention one other thing which may be of interest to some. The 1PPS wave form output from the PRS10 is pretty mediocre. I put the details in another post here sometime back. The Star4 spec is +/- 10ns, something I can only get from my PRS10s with a 74HC7001 shaper. > >> >> A GPS disciplined oscillator contains a GPS receiver which outputs 1PPS >> based on receiving the GPS signals and calculating the position + time >> equation. That PPS signal is noisy in time, it jitters around relative to >> the ideal 1 second period. The GPSDO implements a long time constant PLL >> to synchronize the output of the OCXO to the long term average frequency >> and phase of the GPS PPS, so what you see externally is 10MHz directly >> from the OCXO, 1 Hz (PPS) which is divided down from the 10MHz OCXO, and >> those are controlled by a PLL so that long term the phase of the PPS >> divided down from the OCXO follows the PPS calculated by the GPS receiver, >> but with lower jitter. >> >> -- >> Chris Caudle >> >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. > > Don’t worry about how powerful the machines are. Worry about who the machines > are giving power to. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. Don’t worry about how powerful the machines are. Worry about who the machines are giving power to. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
