[time-nuts] σ vs s in ADEV
magnus at rubidium.dyndns.org
Mon Jan 9 17:07:13 EST 2017
On 01/09/2017 11:00 PM, Bob kb8tq wrote:
>> On Jan 9, 2017, at 4:49 PM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
>> On 01/09/2017 07:41 PM, Scott Stobbe wrote:
>>> I could be wrong here, but it is my understanding that Allan's pioneering
>>> work was in response to finding a statistic which is convergent to 1/f
>>> noise. Ordinary standard deviation is not convergent to 1/f processes. So I
>>> don't know that trying to compare the two is wise. Disclaimer: I could be
>>> totally wrong, if someone has better grasp on how the allan deviation came
>>> to be, please correct me.
>> There where precursor work to Allans Feb 1966 article, but essentially that where he amalgamed several properties into one to rule them all (almost). It is indeed the non-convergent properties which motivates a stronger method.
> A number of outfits were measuring and spec’ing short term stability in the 1950’s and early 1960’s. Some were doing measures that are pretty close to ADEV. Others were doing straight standard deviation of frequency measurements. Since both got tossed up as “short term stability” confusion was the main result. NIST came in (as it rightly should) and gave us a measurement that does converge. They also spend the next two decades
> thumping on a bunch of hard heads to get everybody to use the measurement rather than something with more issues. Once that effort was underway, we got a whole raft of alternatives that each have benefits in certain areas.
> ADEV is far from the only measure that could be properly be used today to characterize short term stability.
Rather, it provides a basic form of measure for which there exist a
number of estimators. The repairment of the 15 years of troubles was
found inn the MDEV as introduced in 1981, providing a new line of
measure. Improvement in estimator degrees of freedom have rendered
variants. The PDEV provides yet improvement over MDEV.
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