[time-nuts] Man with too many clocks.

Peter Reilley preilley_454 at comcast.net
Fri Nov 4 11:35:59 EDT 2016

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 
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 
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 
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 
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?


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 
> 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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