[time-nuts] Mentorship needed in learning about Allan Deviation and variation.

[Magnus Danielson]

On 2020-10-26 15:17, Bob kb8tq wrote:
> Hi
>
> Any practical measure you feed into an ADEV computation will be a look at 
> “device A” versus “device B”. In this case one of them is your GPSDO. What
> is the other device? ( = your TIC has a DUT input and a REF IN, it compares
> one to the other ….). 
>
> If you feed your measurement system with the same signal on both inputs,
> you get a “noise floor” measurement. This *does* have value since it represents
> the best numbers you should ever see out of your system. Checking the
> noise floor is highly recommended …..
>
> ======
>
> One of the wonderful things about going to conferences is the ability to interact
> with folks face to face. The question of “how many samples for ADEV?” was one
> of my favorites. The range of answers turned out to be all over the place. On one
> end, the practical answer of “I plot what I’ve got”. On the other end the statistician's 
> answer of 100 to 250. Both answers generally were also tagged with a lot of
> “that depends” sort of stuff. 
>
> As a practical point, 100 samples for an ADEV plot with Tau = 100,000 is a pretty
> long data run. Most of us don’t have ~4 months to do that sort of run. Indeed one
> of the drivers for various “other” dev measurements has been to improve the 
> confidence with a lower number of samples. 

Already in the 70thies the overlapping ADEV was developed to increase
the estimated degrees of freedom (EDF) to bring confidence intervals
down. Some insist of separating them, but it's scaled the same way, thus
there is no bias, so it's just ADEV. Then David Howe went to discover
the measurement and found it to be missing half the data, and the
TotalDEV was developed and then he went further for Theo.

Oh, Bill Riley have developed a set of exercises to teach people to use
the Stable32. I have made a first round of reviews, and he have improved
them accordingly.

Cheers,
Magnus