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. /tvb ----- Original Message ----- From: "Richard (Rick) Karlquist" <rich...@karlquist.com> To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com>; "Donald E. Pauly" <trojancow...@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. > > πθ°μΩω±√·Γλ > WB0KV > 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 _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
