Ulrich, In the 'bad part...' you mentioned, I wasn't referring to a Rb oscillator but rather the GPS received signal from the satellites. The GPS signal from multiple satellites over a long period of time can be a good 'Transfer Standard'. The atmosphere (moisture, temperature, pressure) are the greatest contributors to GPS short term received stability. By collecting and averaging out the short term (second, minute, day, month) variations over a longer period of time, the variations are smoothed out. This averaged metric is then used to steer the OCXO. No Rb involved.
Tom Tom Duckworth 510-886-1396 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Ulrich Bangert Sent: Wednesday, April 23, 2008 9:44 PM To: 'Discussion of precise time and frequency measurement' Subject: Re: [time-nuts] Disciplining Rubidium Tom, > I think the best of all worlds would be a double-ovenized > SC-cut OCXO running at 5 MHz (lower mass). These OCXOs have > the lowest phase noise and best Allen variance short term > stability (1-100 seconds) of any xtal or Rb. Then have this > OCXO disciplined by the GPS this is the good part of the idea. > with an ephemeris of variations > constantly collected, statically averaged over a long period > (at least 1 month), and the calculated average used to adjust > the OCXO frequency. this is the bad part. Have a look to rb specs concerning environmental changes specially temperature or measure tempco of a rb yourself to see that observation times of this order make no sense! Best regards Ulrich Bangert > -----Ursprungliche Nachricht----- > Von: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Im Auftrag von Tom Duckworth > Gesendet: Donnerstag, 24. April 2008 06:24 > An: 'Discussion of precise time and frequency measurement' > Betreff: Re: [time-nuts] Disciplining Rubidium > > > John, > > I think the best of all worlds would be a double-ovenized > SC-cut OCXO running at 5 MHz (lower mass). These OCXOs have > the lowest phase noise and best Allen variance short term > stability (1-100 seconds) of any xtal or Rb. Then have this > OCXO disciplined by the GPS, with an ephemeris of variations > constantly collected, statically averaged over a long period > (at least 1 month), and the calculated average used to adjust > the OCXO frequency. > > Tom > Tom Duckworth > 510-886-1396 > > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf > Of John Miles > > Sent: Wednesday, April 23, 2008 8:02 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Disciplining Rubidium > > Adding to Tom's worthy list: > > 11) Short-term phase noise; the GPS-Rb sources don't seem to > be as clean as the better GPS-OCXO packages. > > -- john, KE5FX > > > > More precisely, if I had two black boxes, one containing > > > a GPS-Rb-XTAL setup and another containing GPS-XTAL, > > > what measurement would you make from outside the boxes > > > to distinguish from one another? > > > > Ah, clever question. Here's ten ways to distinguish them... > > > > > _______________________________________________ > 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. _______________________________________________ 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.