[time-nuts] Looking for Wavecrest Visi

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Apr 11 19:44:45 EDT 2007


Tom Van Baak wrote:
> 6a
>
>   
>> I used a 100k sample average which yields (IIRC) 200 femtosecond
>> resolution in the 5370B, and for each run checked the min, max, and
>> standard deviation statistics to make sure nothing goofy was going on
>> Standard deviation for a run like that on my 5370B is typically 30 to 40ps.
>>
>> John
>>     
>
> 30-40 ps seems OK to me. But are you saying then that you
> get a measured value to 200 fs resolution but with +/- 30 ps
> standard deviation? This doesn't feel right at all. It seems to me
> if your sdev is +/- 30 ps it is incorrect to even write down the
> measured values to ps levels; and fs are out of the question.
>
> /
>
>
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>   
Tom

I assume the standard deviation is that of the population of 100K 
measurements and not the standard deviation of their mean, which should 
be around 95-126 fs.
Averaging of course does nothing to reduce systematic errors which can 
be as high as 100ps in a 5370A/B. However for cable matching purposes 
systematic errors largely cancel out.

Bruce




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