[time-nuts] Re: 5061B ADEV curves and questions

[john at miles.io]

It's possible that 5061B4 and 5061B6 have noisier tubes, but they are still
basically in spec if you are running in OPER mode.  The PLL does not look
like a brick wall, either in terms of its loop response or the additional
noise contributed by the rest of the lock-in hardware, so the extra
short-term noise you are seeing with the beam turned on looks OK to me.  You
will probably get better performance in LTC mode assuming the units remain
locked.  If you are already running in LTC mode, then I'd say 5061B4 and
5061B6 definitely look noisier than expected between t=1s and t=100s. 

ADEV traces should always be inspected in conjunction with the underlying
data record when you're not sure what's going on.  So, to diagnose the
behavior of 5061B6 past t=1000s, you can (hopefully) look at the
frequency-difference trace to identify when the jumps occurred, how often
they occurred, how long they lasted, and (again, hopefully) what temporary
disturbances might have caused them. 

They are all about 10x better than the HP specifications at t=0.01s.  This
is par for the course, likely because HP didn't update the specs when they
started using 10811s instead of the older cylindrical OCXOs.   You can tell
that 5061B4U has a really nice rock; its ADEV is typical of the best
10811-60109 examples, below 4E-13 @ t=1s and staying in the 13s out to
t=1000s or so.  Around one in ten will do that.

-- john, KE5FX


-----Original Message-----
From: AC0XU (Jim) via time-nuts <time-nuts at lists.febo.com> 
Sent: Monday, July 29, 2024 9:05 PM
To: time-nuts at lists.febo.com
Cc: AC0XU (Jim) <James.Schatzman at ac0xu.com>
Subject: [time-nuts] 5061B ADEV curves and questions

The attached is a plot of some ensemble ADEV measurements of several 5061B
cesium beam oscillators.

Two outlers are interesting to me, and I am wondering if anyone has ideas
about them:

a) 5061B4U was the same unit as 5061B4, but it was obtained when I
accidentally tested the unit with the cesium beam turned off. I expect that
this curve (brown) is the behavior of the undisciplined OCXO. What I am
wondering about is why the unit can't do better than it does up to 300
seconds with the cesium beam turned on. Actually, the same question applies
to all of these units. Ideas?

b) 5061B6 is a unit that, according to all the various meter readings, is
working fine. However, it is evident that it doesn't lock well. Any thoughts
about this one?

Thanks-

Jim