[time-nuts] Is there a good web page introducing ADEV?

[Richard (Rick) Karlquist]

Another great post, Tom.

Amplifying Tom's last paragraph:

1.  The statistics of clocks are (take your pick)

a.  Not gaussian, central limit theorem doesn't apply
b.  Not stochastic
c.  Not stationary
d.  Not ergodic
e.  Contain flicker of frequency processes that do not
average to zero; AKA 1/f noise.

IOW, most of what you think you know about statistics doesn't
apply.  For example, "variance" is undefined because "mean" is
undefined.  It is important to get inside Dave Allan's head in
terms of why he invented this in the first place.

2.  Many poorly informed practitioners are in denial about the
above and resort the measures known as "jitter" or "wander".
These further muddy the water.  They are IMHO, even more difficult
to understand than ADEV.  They have their place (a very narrow one)
but should be disregarded if you want to understand ADEV.

3.  Unlike phase noise, ADEV is a fairly non-intuitive concept.
While there are methods to convert phase noise to ADEV, you
can't go in the other direction.

You sometimes hear the phrase "this is not rocket science".
Well in the case of ADEV, it IS rocket science (or at least
rocket statistics).

Rick N6RK

On 9/24/2020 12:35 PM, Tom Van Baak wrote:
> Hi Hal,
> 
> ADEV turns out to be pretty hard to understand. I took me years for it 
> to sink in. There are web pages, articles, even books. Part of the 
> problem is matching the explanation with the audience.
>