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

EWKehren at aol.com EWKehren at aol.com
Sun Dec 7 20:25:18 EST 2014

We are concentrating on FRK and M 100 but as I mentioned we have been  
sidetracked by GPSDO work for the FE 5680A and FE 405B for the past 18 month. We 
 just got back to our RB's and today I did finish the GPSDO board for the 
FRK and  M 100. These are analog and have a place to insert in the future a 
pressure  sensor. We where working on it last year but had problems with the 
digital  sensor board. To do it right we have to monitor and record 
barometric pressure  and GPSDO behavior and decide how to compensate. It will be 
analog sensor that  will be part of the C field current. Will probably take a 
year, it will be fine  tuning. 
Bert Kehren
In a message dated 12/7/2014 7:15:27 P.M. Eastern Standard Time,  
not.again at btinternet.com writes:

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 
>projects we  find that the limiting factors are the Cesium Standards.  
>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? 
Combining temp control, air pressure compensation and  drift
compensation can give very good results with the right  Rb.


>In a message dated 12/6/2014 10:46:57  A.M. Eastern Standard Time,  
>kb8tq at n1k.org  writes:
>> 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 
>>>> it due to  the fact it had a  bad tube.
>>>> 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 
>re-tubed with a high performance tube is >  $32K.
>>> The stock of “new old stock”  tubes is long gone. About the only  
>you see are pulls from  used gear. The question with them (as with any  
>is just how  many years (or months) is left on the tube. You physically  
>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 
>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 
>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  
>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’
>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 
>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 
>receivers.  Rubidiums do help to some degree. Comparing two  GPS clocks 
>their highly systematic sources, so you can't get useful   differences 
>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 
>Since you can’t  play with the  firmware, you trust that the guy who wrote 
>did a good   job.
>In making a GPSDO, yes on a commercial basis verification  against  
>standards is likely to be required by this or  that customer. In a  
>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 
>good enough.  If your design passes the performance of the ensemble, 
>several of your design is likely to be cheaper than keeping a Cs  running 
> term. That’s even more true if you need a fully  functional 5071A to do 
> comparison. Let’s see .. new BMW or  rebuild the 5071 … hmmm  :)
>> Cheers,
>> Magnus
>>   _______________________________________________
>> time-nuts mailing  list  -- time-nuts at febo.com
>> To unsubscribe, go to   
>>  and follow the  instructions   there.
>time-nuts   mailing list -- time-nuts at febo.com
>To unsubscribe, go to   
>and  follow the  instructions  there.
>time-nuts  mailing list -- time-nuts at febo.com
>To unsubscribe, go to  
>and follow the  instructions there.

More information about the time-nuts mailing list