Hi
> On Dec 7, 2014, at 7:15 PM, Angus <not.ag...@btinternet.com> wrote: > > On Sat, 6 Dec 2014 11:47:10 -0500, you 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 > > Hi Bert, > > Out of curiosity, what Rb are you using, and how does it respond to > air pressure changes? Properly identifying / measuring pressure induced drift is not as easy as one might think. The “tweak and see” approach seems to be the best bet. Hmm … I wonder who originally suggested that …. oh, yea it was Angus. Bob > Combining temp control, air pressure compensation and drift > compensation can give very good results with the right Rb. > > Angus. > >> >> In a message dated 12/6/2014 10:46:57 A.M. Eastern Standard Time, >> kb...@n1k.org writes: >> >> Hi >>> On Dec 6, 2014, at 10:35 AM, Magnus Danielson >> <mag...@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) >> <drkir...@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. Its 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, GPSDOs are the more useful device. Their >> performance rivals that of most of the older Cs standards. They are way >> cheaper, >> and they dont wear out. Indeed, if you have a 5071A with a high >> performance tube in it, a GPSDO is not going to match its performance. Ive >> >> 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 its 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 cant 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, Im not so sure thats 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. Thats even more true if you need a fully functional 5071A to do the >> comparison. Lets see .. new BMW or rebuild the 5071 > hmmm :) >> >> Bob >> >>> >>> Cheers, >>> Magnus >>> _______________________________________________ >>> 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. >> _______________________________________________ >> 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. _______________________________________________ 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.
