[time-nuts] Tbolt issues

Bob Camp kb8tq at n1k.org
Thu Sep 1 16:44:52 EDT 2016


I think one issue here is that ADEV is being used by one “lab" and absolute frequency is being used by the other. 
They very much are *not* the same thing. There isn’t even a really simple way to convert one to the other. 
There will always be a big delta between those two measures. For absolute frequency you will also need
some sort of confidence number (99 % or some such thing). The details of why all this happens are the
mainstay of the 1960’s (and early 70’s) papers on ADEV. 


> On Sep 1, 2016, at 3:11 PM, Tom Van Baak <tvb at LeapSecond.com> wrote:
> Hi Bert,
>> because the frequency is constantly changed to correct  time.
> A simple answer: you may have a bad TBolt. Was it part of the TAPR group buy, or did you buy it from eBay/China? If TAPR, you get a free replacement. Contact me off-list.
>> Tbolt is an excellent time device but not good for frequency reference  past 1E-10.
> No, again it sounds like you have a bad TBolt. Or something is wrong (antenna? reception? time constant? environment? China resoldered parts?). I appreciate that Juerg did lots of testing -- do you happen to have his ADEV plot?
> I'm willing to help you debug this.
> (1) Attached is the ADEV of 8 random TBolts that I tested recently. How does this compare to yours? You can see mine are all under 2e-12 at 1 s and under 4e-12 at 100 s. On a bad day during holdover it might climb to 1e-11 at 1000 s but when locked GPS disciplining takes over and keeps it down to 2 or 3e-12.
> (2) For locked vs. unlocked TBolt ADEV, see http://www.leapsecond.com/pages/gpsdo/
> (3) Also attached is a frequency plot showing the typical noise and wander, down at the 1e-11 level. How does this compare with yours?
> Your claim of 1e-10 is order(s) of magnitude worse than the TBolts that I see. Something is wrong.
> /tvb
> ----- Original Message ----- 
> From: "Bert Kehren via time-nuts" <time-nuts at febo.com>
> To: <time-nuts at febo.com>
> Sent: Thursday, September 01, 2016 9:54 AM
> Subject: [time-nuts] Tbolt issues
>> We have been following the Tbolt power discussions but what I am missing is 
>> the main problem with Tbolts. All the power work will not improve the 
>> frequency  performance of the unit because the frequency is constantly changed 
>> to correct  time. Tbolt is an excellent time device but not good for 
>> frequency reference  past 1E-10. I noticed it when I bought it and compared it with 
>> my Tracor 527E on  the needle and ever since used an Austron 2110 with a 
>> digital 100 sec. loop for  clean up. My Swiss partner Juerg has relied on an 
>> OSA F3 for Tbolt clean up but  continuous bad results on our work resulted in 
>> a detailed analysis using a  HP53132A counter and M100, FTS44060, two 
>> OSA8600's and one of the best FE405's.  The rsult is that the OSA F3 does not 
>> clean up the Tbolt and we see +-4E-11  changes and old data shows even some +-8 
>> E-11 excursions. With the popularity of  the Tbolt an analog or digital 
>> clean up loop would make sense. We are working on  both, the analog because I 
>> saw similar behavior on the FE5680 and FE5650, we did  a GPSDO but do not plan 
>> on using those Rb's but focus on M100 and FRK. 
>> The collective expertise of time nuts could make a significant  contribution
>> For power in critical applications we use the excellent work from Bern Kaa  
>> a friend for the last twenty years and well known because of his published 
>> work  in the European HAM community
>> Bert Kehren
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