[time-nuts] Hadamard variance
Steve Rooke
sar10538 at gmail.com
Fri Apr 10 11:50:46 UTC 2009
It looks like there is a need for more tools to not only modify the
data but to analyse the raw data to measure parameters like linear and
logarithmic drift. I guess plain old statistics should give this sort
of information.
73,
Steve
2009/4/10 Tom Van Baak <tvb at leapsecond.com>:
>> Steve
>>
>> Just dont get too carried away.
>> Remember that the Hadamard deviation is only insensitive to linear
>> frequency drift.
>> If the drift is quadratic for example then it will affect the Hadamard
>> deviation.
>>
>> Bruce
>
> Correct. This is another reason why the practice of removing
> systematic drift from raw data first and then computing ADEV
> on the residuals is quite useful.
>
> It allows you to separate the task of modeling systematic effects
> from the calculation of stability (ADEV) of the residuals.
>
> For example, you may suspect ahead of time, or you may find
> through analysis, that your DUT is following a slow logarithmic
> drift trend rather than just linear drift. Either way, you can remove
> the systematic effect to get to a closer measure of the intrinsic
> stability limits of the DUT.
>
> This is common with OCXO which have aged, say more than
> a few days, but less than a few months. It's pretty cool to see
> very linear drift rates each day, but to also notice that the rate
> itself slowly decreases week by week.
>
> As another example, you may find a strong correlation between
> temperature and frequency. You could plot ADEV of the raw
> data, and then plot ADEV of the temperature compensated
> residuals and observe the difference in the plots.
>
> /tvb
>
>
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--
Steve Rooke - ZL3TUV & G8KVD & JAKDTTNW
Omnium finis imminet
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