[time-nuts] Fwd: HP5061B Versus HP5071 Cesium Line Frequencies
Tom Van Baak
tvb at LeapSecond.com
Sat May 27 21:27:34 EDT 2017
I agree with some of what Donald and Rick are saying.
But does anyone actually use a locked Cs standard for its short-term stability (e.g., tau < 10 s)? If that's your goal then what you do is run the standard in Cs-Off (free-run, standby) mode. Or just use best old OCXO you can find and forget the cesium entirely. I don't use a 5061/5071 as a short-term ref. For that a hand-picked FTS 1000/1200-series, or hp 10811, or Wenzel ULN, or BVA is much better. It's rare that you need both extreme long-term accuracy and extreme short-term stability at the same time, so this approach works well.
So while I'm eager to see Donald's results, I question their merit. The 5061 standards already have a very convenient Cs-Off switch right on the front panel. It is there so you get the pure 10811 performance when you need it. Use it. In fact there's lots of people run their precious 5061 in Cs-Off mode 23.9 hours a day and just turn on the Cs once a day, or once a week, to re-cal the oscillator. It's not there just to conserve cesium; you also get full 10811 short-term performance. Note also some 5061 have a short/long time-constant switch which also helps you tailor the ADEV you want out of the instrument.
----- Original Message -----
From: "Richard (Rick) Karlquist" <richard at karlquist.com>
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>; "Donald E. Pauly" <trojancowboy at gmail.com>
Sent: Saturday, May 27, 2017 5:15 PM
Subject: Re: [time-nuts] Fwd: HP5061B Versus HP5071 Cesium Line Frequencies
On 5/27/2017 2:08 PM, Donald E. Pauly wrote:
> I am investigating the total redesign of the HP5061B lock system for
> vastly improved performance. It looks like the performance of the
> HP5071A can be beaten by 10 to 1 for averaging times on the order of a
> few seconds.
That's an interesting claim, but it could be valid.
The 5071A flywheel is a 10811 selected for performance
and modified to have additional electronic tuning
range (I was involved in that) but otherwise it is
plain vanilla 10811. At a few seconds averaging time,
this oscillator is basically open loop. It might be
possible to improve a 5071A by simply finding a 10811
with exceptional short term stability. The tail of
the distribution curve went down at least an order of
magnitude, according to Jack Kusters at HP.
In any event, you could use an unmodified 5071A or maybe
a 5061B high performance option and discipline some
really good XO. Certainly, the 10811 isn't the world's best
XO. You'll need to prevent your XO from getting bothered
by microphonics, stray magnetic fields, 2G turnover, temperature
fluctuations, and humidity if not hermetic , etc. The 5071A is
impervious to all that as it is.
Is that what you had in mind?
I remember before I worked for HP visiting JPL's Goldstone
tracking station. They had a 5061A that disciplined a
hydrogen maser for VLBI. They said a plain 5061A was useless for their
work. OTOH, a hydrogen maser without drift correction was
also useless for their work. They had a huge room with 100's
of racks of equipment, but the 5061A and H maser had their
own dedicated room.
Rick Karlquist N6RK
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