[time-nuts] 53230A noise floor

Anders Wallin anders.e.e.wallin at gmail.com
Fri Apr 3 15:48:23 EDT 2015


>
>
> See the part the end that shows why averaging breaks ADEV:
>     http://leapsecond.com/pages/adev-avg/
>

Hi Tom, thanks for reminding me of that page. I did no averaging of the
data myself, and I think it's logical that the counter noise floor goes
down with increasing gate time - I just haven't had time to read and think
about the counter specs enough to write down some reasonable formula that
predicts the noise floor for different gate times.
PHK's comment about trying something different than exactly 10MHz is worth
testing.

Reading your page above I am confused by the graph where you add noise.
If I create a synthetic phase dataset with 1 ns of RMS noise (i.e. you
histogram the data and it looks like a gaussian with standard deviation
1ns) and then calculate ADEV I get ADEV(1s) = sqrt(3)*1e-9  (tried with
both stable32 and allantools)
Your page says "add 1ns noise" and shows ADEV(1s)=1e-9. Can you clarify
what "add 1ns noise" means - or am I doing something wrong?

Anders


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