[time-nuts] Tbolt issues

EWKehren at aol.com EWKehren at aol.com
Thu Sep 1 17:11:56 EDT 2016


For us it is absolute Frequency, to me it is a measure of true  performance.
 
 
In a message dated 9/1/2016 4:52:35 P.M. Eastern Daylight Time,  
kb8tq at n1k.org writes:

Hi

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.  

Bob


> 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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