[time-nuts] Omega counters and Parabolic Variance (PVAR)

Chuck Harris cfharris at erols.com
Tue Jul 14 17:46:26 UTC 2015


Hi Magnus,

Am I understanding correctly that the difference between Pi, Delta, and Omega
is basically one of software processing after the sample is made?

If so, how can this be best leveraged by those of us that have 5370A/B counters
that are running John Seamon's enhanced BBB processor in place of the original
5370 Motorola processor?

Thanks!

-Chuck Harris

Magnus Danielson wrote:
> Fellow time-nuts,
>
> Since I haven't seen any reports on this, I though I would write down a few lines.
>
> While normal counters use a pair of phase-samples to estimate the frequency, now
> called Pi counters (big pi, which has the shape of the weighing function of frequency
> samples), counter vendors have been figuring out how to improve the precision of the
> frequency estimation for the given observation time. One approach is to overlay
> multiple measurements in blocks, which for the frequency estimation looks like a
> triangle-shape weighing, so this type of counter is referred to as Delta counters
> (again to resemble the shape).
>
> Classical counters of the Pi shape is HP5370A, SR620 etc.
> Classical counter of the Delta shape is the HP53132A.
>
> However, counters using the Linear Regression methodology does not fit into either of
> those categories. Enrico Rubiola derived the parabolic shape of the weighing function
> (which I then independently verified after we spoke during EFTF 2014), and he then
> passed on the results to Francois Vernotte and other colleagues to continue the
> analysis.



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