[time-nuts] Tbolt issues

Tom Van Baak tvb at LeapSecond.com
Thu Sep 1 15:11:22 EDT 2016


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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