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 <[email protected]> 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 < > [email protected]> 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, > > [email protected] writes: > > > > Hi > >> On Dec 6, 2014, at 10:35 AM, Magnus Danielson > > <[email protected]> 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) > > <[email protected]> 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 > >> _______________________________________________ > >> time-nuts mailing list -- [email protected] > >> To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >> and follow the instructions there. > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
