[time-nuts] Man with too many clocks.

Bob Camp kb8tq at n1k.org
Fri Nov 4 13:48:02 EDT 2016


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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