Hi A ten or twenty turn pot on a normal EFC will get you past the point that you can reasonably set the oscillator. The typical (not GPS version) EFC is down around 1 to 2 x 10^-7. A 20 turn pot will be running 1x10^-8 per turn. 100 to 200 points per turn is a pretty typical “set” number for a pot. That gets you into the sub 1x10^-10 region. The OCXO’s we are talking about have a temperature, pressure and humidity coefficient that each are well above that level.
Bob > On Nov 4, 2016, at 2:31 PM, Scott Stobbe <[email protected]> wrote: > > I'm not sure if there is a reason counters don't let you digitally > calibrate beyond that, the 10 MHz ref out on the rear panel would still be > out of cal. > > On Fri, Nov 4, 2016 at 1:48 PM, Bob Camp <[email protected]> wrote: > >> Hi >> >> The only practical way to set the 10811 or 10544 is with a >= 10 turn pot >> on the EFC. I >> never have worked out just why there are so many instruments that don’t >> have a pot on >> the EFC. >> >> Bob >> >>> On Nov 4, 2016, at 11:35 AM, Peter Reilley <[email protected]> >> wrote: >>> >>> I gave up on trying to use the GPS 1 PPS signal to calibrate the 10 MHz >> OCXO's that >>> I have. The reason that others have pointed out is that the >> uncorrected 1 PPS >>> signal from the GPS is has just a little too much a jitter to use it for >> calibration >>> with your eye using a scope. If it were sawtooth corrected then it >> would be better >>> but you really need a GPS disciplined oscillator. >>> >>> Not to be outdone, I brought out a rubidium oscillator that I had put >> away because >>> it did not appear to work properly. It only put out a 1 PPS signal and >> nothing else. >>> I compared that with the GPS PPS and could get a good comparison on the >> scope. >>> The rubidium drifted about 40 nS over 12 hours. So it seemed to be >> good. >>> >>> With that I could adjust the OCXO's in my 5370's. The spec for the HP >> 5370B with >>> a HP 10811 OCXO is better than 1 X 10^-10 RMS for 1 sec average. That >> is, it should >>> take more than 1,000 seconds for one 10 MHz wave to shift by 360 >> degrees. That >>> is very hard to do using the screw adjustment in the OCXO. Even the >> slightest >>> movement possible will cause a frequency change greater that is >> spec'ed. How >>> do cal labs do it? >>> >>> My HP 5370A has a 10544 OCXO which is spec'ed for short term stability of >>> better than 1 X 10^11 for 1 second. Even better than the 5370B! The >> adjustment >>> screw is much coarser and it is not possible to get any better than a >> few seconds for >>> one cycle phase shift of the 10 MHz OCXO against the standard. It >> seems that I can't >>> get even close to the spec. >>> >>> These have been running for a few days. It that enough? >>> >>> Pete. >>> >>> >>> >>> On 11/3/2016 8:20 AM, Peter Reilley wrote: >>>> I am the proverbial man with too many clocks and I don't know what time >> it is. >>>> To correct this situation I have decided to calibrate everything. >>>> >>>> I have a HP 5370B, a HP 6370A, and a HP 5328A all with the TCXO >> option. I also >>>> have some TCXO modules. I figured that I would calibrate them against >> my Trimble >>>> Resolution T GPS receiver. >>>> >>>> I put the 1 PPS signal in one channel of my scope and one of the 10 MHz >> TCXO >>>> signals in the other channel and look at the phase relationship. The >> TCXO's are >>>> already close enough that I should not be out by more than a fraction >> of a waveform. >>>> I understand that I have to deal with the 1 PPS without sawtooth >> correction. >>>> >>>> I expected to see the 10 MHz signal bounce around but not move more >> than 1/2 >>>> of a wave length. Instead I see the 10 MHz waveform appear steady for >> a few seconds >>>> then jump a significant portion of the wave. The jump is too much to >> be confident >>>> that I have not slipped one cycle. >>>> >>>> Can I do what I am trying to do or am I missing something? >>>> >>>> Pete. >>>> >>>> _______________________________________________ >>>> 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.
