[time-nuts] Man with too many clocks.

Scott Stobbe scott.j.stobbe at gmail.com
Fri Nov 4 14:31:10 EDT 2016


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 <kb8tq at n1k.org> 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 <preilley_454 at comcast.net>
> 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.
> >>
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