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

Magnus Danielson magnus at rubidium.dyndns.org
Wed Nov 22 20:35:33 EST 2017

Hi Ralph,

On 11/23/2017 12:38 AM, Ralph Devoe wrote:
> Hi Time-nuts and Attila,
>           Thanks for the very interesting and informative criticisms. That
> is what I was looking for.  I don't agree with most of them, but I need
> some time to work out some detailed answers.

There is some tough love here, but learned the hard way many times.
Some of it will take time to grasp and accept, but so far all I've seen 
have been constructive criticism.

>            To focus on the forest instead of the trees:  The method uses a
> $300 student scope (Digilent Analog discovery- a very fine product), which
> any skilled amateur can modify in a weekend, and produce a device which is
> 10-100 times better than the expensive counters we are used to using.  The
> software contains only 125 lines of Python and  pretty much anyone can
> write their own. In practice this device is much easier to use than my
> 53132a.

There exist several works that have used SDR approaches to measure 
phase. It is not new and unknown. The Microsemi phase-noise and 
stability test-sets is good examples.

This is not to say that there is no value in looking at what can be 

What you do is just a variant of heterodyne receiver, and essentially a 
DMTD using ADCs and phase estimation using least square filtering. It 
just takes a few re-drawing stages to show that.

You would need to show how the phase estimation is actually done on that 
signal, the given explanation is not very helpful as it sketches the 
processing and hands of to some library. This crucial point should be 
handled with more care and detail. Using such a least-square fit, I want 
to understand how the phase is estimated in such non-linear function.

Also, you should compare to I/Q demod, arctan and a truly linear least 

Already the title is interesting, since it is really not Allan Variance 
measurement as such but phase measurement, which then can be used to 
produce Allan Deviation measures.


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