[ntp:questions] Allan deviation survey

Miroslav Lichvar mlichvar at redhat.com
Fri Sep 10 18:10:44 UTC 2010


On Fri, Sep 10, 2010 at 04:05:29PM +0000, unruh wrote:
> Except yo uknow that the typical computer clock is driven mostly by
> temperature variations, and those are time of day dependent. People
> tend to work during the day thus their computer works during the
> day, and does not at night. Ie, there is a very strong daily cycle
> in the temp of the computer. That is NOT within the Allan model, and
> the Allan variation and minimum are really irrelevant with this
> highly non-stochastic noise model.

At least in my tests, the effect of temperature varitions shows up as
a huge bump in the plot. The oscillator's random-walk frequency noise
normally shown as +1/2 slope may not be visible, but I don't really
need it.

>From comparing results from simulations on data captured from PPS and
simulations on generated frequency noise, it seems that simply using a
stronger frequency noise is good enough to get similar results as with
real data.

What I'm hoping to get from the survey is a range for random-walk
frequency noise which will give results similar to real oscillators
and which I should focus on in my simulations.

-- 
Miroslav Lichvar



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