[time-nuts] ADEV with very short Tau

WarrenS warrensjmail-one at yahoo.com
Wed Apr 29 12:35:00 EDT 2015


>what is the simplest method to measure sub second ADEV?

The answer depends on many unstated things.
Among them is your definition of simple, the Frequency of the DUT, the noise floor, your budget and your available time.. 

After budget and frequency, the next most important thing is the noise floor or resolution that you want.
Many of sub second ADEV plots you see end up showing the limitations of the tester and not the DUT.

One answer
If you want meaningful ADEV numbers at 0.1 sec, it is best to sample at >= 20 samples per second.
I find sampling at line freq or its multiple  has several advantages to allow good repeatable results for 0.1 sec ADEV.
For North American  that means a sample rate of 60 or 120Hz.

If you want to test Time-nut type oscillators with ADEV's below 1e-11 then you will need something with sub Pico second resolution.
Also measuring a  frequency of  5 or 10 MHz, instead of measuring say a 20 pps divided down signal has many advantages.

After defining the frequency and resolution you want, it comes down to what you mean by "simple"..

If you need to do it just once,  find a Time-nuts that already has the right capability and is willing to measure it for you.
If simples does not include budget get a TimePod.
If simple includes low cost and you need a low noise floor, then you're going to have to consider some custom built thing.
Who is doing the building, depends on how you value your time.



I know how to measure ADEV with frequency method (using a 53131A counter) or time difference method (using 1 PPS of a GPSDO for example) but I would like to measure ADEV in the sub-second domain (from 0.1s to 1s for example). Do I need a Time Interval Analyzer, if so, an HP 5371A is ok for that ? Or there are simpliest method ?

Thanks for your advices.


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