[time-nuts] Tbolt issues

[Lars Walenius]

Hello Tom,

What are the conditions for your charts? Are the Tbolts in locked condition or holdover? If locked what settings do you have for time constant and damping? Is it any other setting that is important?

For the frequency chart I see excursions up to +-3E-11 so not so far from the values that Bert gives and as I understand his TBolt might have a default setting of 100 seconds.

Lars


Från: Tom Van Baak<mailto:tvb at LeapSecond.com>
Skickat: den 1 september 2016 21:12


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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