[time-nuts] OCXO noise as they retrace

[Bob Stewart]

Hi John,
That is a thought.  The 1s ADEV had been very stable across units until just now.  But, I don't know how to look at the beam current.  There is a "Monitor3" program that I can use (see link below) that can plot the Clock Servo values, as well as Zeeman Servo, Gain Servo, CBT Supplies, and Power Supplies.  It collects values each 10 seconds.  Which one(s) of these would have the most relevance?  

http://ae6rv.com/PRS-45A/Monitor3.png

I'll go ahead and run an ADEV of the 10811 in the 5370 against the PRS-45A.
Bob -----------------------------------------------------------------------------------
GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info

      From: John Miles <john at miles.io>
 To: 'Discussion of precise time and frequency measurement' <time-nuts at febo.com> 
 Sent: Monday, June 27, 2016 7:50 PM
 Subject: Re: [time-nuts] OCXO noise as they retrace
   
> I've had a specific GPSDO running for some time now, and I notice that the
> noise at tau 1s has gotten worse as the retrace flattens out.  In this case,
> the  ADEV was about 3.6E-11 a month or so ago, and has now gone up to about
> 8.5E-11.  (Measurements performed by a 5370A against a PRS-45A Cs
> standard.)  Is this normal as the startup drift settles out?  It's been on the same
> power supply module during this time, but I have been using it to test new
> code, so the DAC has been cycled from midpoint to lock numerous
> times.  Another unit that's been running for some time has done essentially the
> same thing.
> Weather?  Environment?  GPS demons?
> 

Are you sure it's not the PRS-45A?  Cs standards get noisy as the tube ages, typically becoming much noisier before failing entirely.  This is usually pretty easy to diagnose by watching the beam current fluctuate.

You're also bumping up against the limits of what your counter can do.  Readings in the 4E-11 to 8E-11 range at t=1s are common with 5370s, depending on any number of factors.  

-- john, KE5FX
Miles Design LLC


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