[time-nuts] Allan variance by sine-wave fitting

Attila Kinali attila at kinali.ch
Mon Feb 26 06:47:09 EST 2018

On Mon, 26 Feb 2018 02:43:04 -0800
"Tom Van Baak" <tvb at LeapSecond.com> wrote:

> This note is a follow-up to Ralph Devoe's ADEV posting earlier this month.
> It's a long story but last week I was in the Bay Area with a car full of 
> batteries, BVA and cesium references, hp counters, and a TimePod. I was able 
> to double check Ralph's Digilent-based ADEV device [1] and also to 
> independently measure various frequency standards, including the actual 5065A 
> and 5071A that he used in his experiment.
> For the range of tau where we overlap, his ADEV measurements closely match my 
> ADEV measurements. So that's very good news. His Digilent plot [2] and my 
> TimePod / TimeLab plot are attached.

Nice. Thank you!

BTW: Do you know the cause of the oscillations in the 5065 vs BVA plot?

> I'm sure more will come of his project over time and I hope to make 
> additional measurements using a wider variety of stable / unstable sources, 
> either down there in CA with another clock trip or up here in WA with a clone 
> of his prototype. It would be nice to further validate this wave fitting 
> technique, perhaps uncover and quantify subtle biases that depend on power 
> law noise (or ADC resolution, or sample rate, or sample size, etc.), and also 
> to explore environmental stability of the instrument.

For this, we would need a better understanding of what noise is 
mathematically and how it is affected by various components in
the signal path. But our mathematical description is lacking
at best (we only can descirbe white and 1/f^2 noise properly).

			Attila Kinali
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson

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