[time-nuts] Did a member of time-nuts buy this?

paul swed paulswedb at gmail.com
Sat Dec 6 12:58:18 EST 2014


Well a bad tube is a bad tube and thats been my story. Though for $125 how
can I complain. But for $999 plus $79 shipping no interest at all.
When the tubes used up its used up. Generally.
Regards
Paul
WB8TSL

On Sat, Dec 6, 2014 at 12:06 PM, Bob Camp <kb8tq at n1k.org> wrote:

> Hi
>
> If you toss a Rb into the GPSDO “mix” things can get quite good. The Rb
> *should* be better than an OCXO in the > 1,000 second range. It’s crossover
> with the GPS ADEV will be further out than the OCXO’s. The gotcha with both
> the OCXO and Rb is their temperature dependance. Some / many / all of the
> lower cost Rb’s are not much better than a good double oven OCXO in terms
> of raw temperature performance. The approach they use to “correct” this
> does not help their ADEV at all. Yes, you can disable the correction and
> put the whole thing in a temperature controlled environment.
>
> Lots of details to take care of. If you get them all right, you’ll beat
> any / all of the older Cs standards. That *assumes* that GPS is not
> deliberately lying to you :) … (off to the Conspiracy Time Nuts mailing
> list). One very cute addition would be to pull down the NIST GPS data and
> use it to correct your system on an hourly / daily basis. If you do that
> with common view satellites, you most certainly will beat a surplus grade
> Cs standard.
>
> Bob
>
> > On Dec 6, 2014, at 11:47 AM, Bert Kehren via time-nuts <
> time-nuts at febo.com> wrote:
> >
> > I am looking forward to long term data on the Lucent unit. GPSDO's are
> > getting closer and closer to Cesium. Having worked for 18 month on two
> GPSDO
> > projects we find that the limiting factors are the Cesium Standards.
> Working
> > presently on a Cesium GPSDO. Short term OCXO, medium Rb and long term
> > Cesium.  With Cesium may be able to use 14 day filter. Will find out. If
> we  do
> > not see an improvement we will most likely retire our Cesium units.
> > Bert Kehren
> >
> >
> > In a message dated 12/6/2014 10:46:57 A.M. Eastern Standard Time,
> > kb8tq at n1k.org writes:
> >
> > Hi
> >> On  Dec 6, 2014, at 10:35 AM, Magnus Danielson
> > <magnus at rubidium.dyndns.org>  wrote:
> >>
> >> Bob,
> >>
> >> On 12/06/2014 04:16 PM, Bob Camp  wrote:
> >>> Hi
> >>>
> >>>> On Dec 6, 2014, at 9:54 AM,  Dr. David Kirkby (Kirkby Microwave Ltd)
> > <drkirkby at kirkbymicrowave.co.uk>  wrote:
> >>>>
> >>>> I see this cesium reference on eBay,  where apparently someone
> returned
> >>>> it due to the fact it had a  bad tube.
> >>>>
> >>>>
> >
> http://www.ebay.com/itm/HP-Agilent-5061A-Cesium-Beam-Frequency-Standard-FOR-PARTS-REPAIR-/141483787108
> >>>>
> >>>> I'm wondering if it was someone on this list. It is likely to  be
> >>>> practical to replace the tube?
> >>>>
> >>>
> >>> New tubes for Cs standards are in the >$20K range. Getting a  modern
> one
> > re-tubed with a high performance tube is > $32K.
> >>>
> >>> The stock of “new old stock” tubes is long gone. About the only  tubes
> > you see are pulls from used gear. The question with them (as with any
> Cs)
> > is just how many years (or months) is left on the tube. You physically
> move
> > Cs from one end of the tube to the other when you operate the device. One
> > you have exhausted the pre-loaded stock, the tube is dead. It’s also
> coated
> > all over the inside with surplus Cs. Since signal to noise ratio is very
> > important, the drop in Cs at end of life and crud on the inside leads to
> > degradation in the performance towards the end of the tube life. Even if
> the
> > tube works, it may (or may not) be useful in a given application.
> >>>
> >>> For many applications, GPSDO’s are the more useful device. Their
> > performance rivals that of most of the older Cs standards. They are way
> cheaper,
> > and they don’t wear out. Indeed, if you have a 5071A with a high
> > performance tube in it, a GPSDO is not going to match it’s performance.
> I’ve
> > replaced two tubes in one of those, so they are correct when they talk
> about  the
> > projected life of the tube.
> >>>
> >>> The other subtle  issue with Cs standards is shipping. If you are going
> > to do it “right” it’s a  major pain. Sending one back for re-tube does
> > require you to do all the formal  shipping nuttiness. That may or may
> not be an
> > issue on the surplus market  ….
> >>
> >> Well, there is one use-case for a cesium, which is the  validation of
> GPS
> > receivers. Rubidiums do help to some degree. Comparing two  GPS clocks
> with
> > their highly systematic sources, so you can't get useful  differences
> that
> > way for the stability of the produced signal.
> >
> > Unless  you are making a GPS receiver from scratch (which you might be),
> > there is a  certain “trust factor” that comes into using a GPS for
> timing.
> > Since you can’t  play with the firmware, you trust that the guy who
> wrote it
> > did a good  job.
> >
> > In making a GPSDO, yes on a commercial basis verification against
> primary
> > standards is likely to be required by this or that customer. In a
> basement
> > lab, I’m not so sure that’s true. Simply comparing things against an
> > ensemble of “known good” designs (and cross checking the results) should
> be
> > good enough. If your design passes the performance of the ensemble,
> building
> > several of your design is likely to be cheaper than keeping a Cs running
> long
> > term. That’s even more true if you need a fully functional 5071A to do
> the
> > comparison. Let’s see .. new BMW or rebuild the 5071 … hmmm  :)
> >
> > Bob
> >
> >>
> >> Cheers,
> >> Magnus
> >> _______________________________________________
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