The GPS's PPS wanders but it can be used to have an idea whether your Rb is fast or slow. How much the wander will be, depends on the type of GPS receiver, the antenna position and the survey, the GPS clock granularity (the sawtooth). Given a suitable amount of time (5 minutes, for example) you can see if the Rb PPS is fast or slow. I have measured up to 200nS of PPS peak-to-peak wander using a Z3815A as a reference.
On Thu, Sep 19, 2013 at 1:37 AM, Bob Stewart <[email protected]> wrote: > Hi John and Azelio, > > The problem with the GPS 1PPS is the +/- 52ns sawtooth. Without some magic > hardware, you're left with using a stable 1PPS and then calibrating that to > the correct frequency. If my software does what my math says it does, then > my OCXO is very close to correct. Testing is time consuming to say the least. > > Bob > > > > > >>________________________________ >> From: "John C. Westmoreland, P.E." <[email protected]> >>To: Discussion of precise time and frequency measurement <[email protected]> >>Sent: Wednesday, September 18, 2013 6:13 PM >>Subject: Re: [time-nuts] GPSDO vs Rb standard >> >> >>Azelio and Fellow Time Nuts, >> >>Isn't the GPS 1PPS signal supposed to be 'precise' to within what error? I >>imagine this is in the specs of the specific receiver - >>but I was wondering if some of you have actually measured what that is - >>and could report the numbers that you have found. >> >>Thanks! >>John Westmoreland >> >> >> >>On Wed, Sep 18, 2013 at 3:07 PM, Azelio Boriani >><[email protected]>wrote: >> >>> Instead of using the Rb's PPS, use the GPS receiver's PPS. Maybe you >>> will find out that the Rb is slow... you can also check the Rb's PPS >>> against the GPS's PPS. >>> >>> On Wed, Sep 18, 2013 at 11:47 PM, Bob Stewart <[email protected]> wrote: >>> > I hooked the Rb's 1PPS to the trigger input on my old Tek 455, 10MHz >>> > GPSDO to Channel A, .05us trace, and turned the lights out so I could >>> > see it. The 10MHz is marching right to left about 1 cycle every 20 >>> > seconds. So, can I say that the Rb considers my GPSDO to be too fast by >>> about 5ppb? >>> > >>> > >>> > Bob >>> > _______________________________________________ >>> > time-nuts mailing list -- [email protected] >>> > To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> > and follow the instructions there. >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >>_______________________________________________ >>time-nuts mailing list -- [email protected] >>To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>and follow the instructions there. >> >> >> > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
