Hanging bridges out of a GPSDO's PPS? Interesting... time to try to setup a measurement and see the relation between the GPS's PPS hanging bridges and the corresponding DO's ones. On Tue, Aug 14, 2018 at 9:55 AM Mike Cook <[email protected]> wrote: > > > > 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.
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