[time-nuts] Re: HP 10811-60111 Oscillators {External}

[John Miles]

> -----Original Message-----
> From: Jim Muehlberg via time-nuts [mailto:time-nuts at lists.febo.com]
> Sent: Wednesday, January 11, 2023 7:40 AM
> To: time-nuts at lists.febo.com
> Cc: Jim Muehlberg
> Subject: [time-nuts] Re: HP 10811-60111 Oscillators {External}
> 
> Bob, so the ADEV gets better than factory spec - better over time?  The
> number stated below approaches NIST_F1 at 1s ~2.8E-13. (Not sure if its
> correct - found on a slide presentation) and apparently exceeds most
> commercial cesium clocks for time scales less than~10s.. 

A couple of weeks is usually enough for an OCXO to reach its best stability at taus in the 100-1000 second range.   Sometimes you do encounter good crystals that are jumpy at first and need some extra time to settle down, and in those cases, the ones that show visible improvement in the first few days are worth waiting out.  But generally an OCXO that is not improving after a week is unlikely to straighten up and fly right in another month/year/decade.  

Of course, if the oscillator is brand new or has been powered off for years, then it may take weeks or months to achieve its best performance at taus >> 1000 seconds due to rapid-aging effects.

Like Bob, I've tested quite a few 10811s and have seen a few reach the 3E-13 level at t=1s.  That's good enough to justify going through a lot of clunkers to find the gems.  Also as he points out, any 10811-xxxxx can be "one of the good ones."  The -60109 parts used in the atomic standards will be among the best but are not necessarily *the* best, so you've gotta test 'em all.  

Regarding NIST-F1 and other exotic clocks, those are often designed to interrogate the underlying quantum process at discrete intervals and adjust their OCXO periodically, rather than maintaining a traditional closed loop.  So when you see low -13s or high -14s near t=1s, you are probably looking at the performance of an ultrastable OCXO rather than the clock transition itself.  Not sure if that's true for the fountain clocks in particular, but it's how some of the trapped-ion standards work. 

-- john