[time-nuts] Mains frequency

[Bill Dailey]

I meant ideal at the noise floor of the picPET (i.e in this case the
generated 60Hz).


On Mon, Nov 18, 2013 at 8:08 PM, Bob Camp <lists at rtty.us> wrote:

> Hi
>
> An “ideal” curve would go to the bottom of the scale as soon as the plot
> started. Anything that shows on the ADEV curve is by definition noise. The
> slope of the ADEV curve can help you determine what sort of noise it is.
> The slope(s) on an modified ADEV curve can do that slightly better.
>
> Bob
>
> On Nov 18, 2013, at 8:03 PM, Bill Dailey <docdailey at gmail.com> wrote:
>
> > tom,
> >
> > nice plots.  how do you figure out what the contribution of variability
> vs
> > noise? In other words there is a differential between the "ideal" and the
> > actual a dev curves... is there a way to tease out how much nose
> contribute
> > to that differential?  It does seem to me that there should be far less
> > short term variability (< 100s) than there appears to be.  Clearly in the
> > very short tau (< 0.1 s) the picPET can't tease that out but as the
> curves
> > diverge, how much of that is noise? between say 0.1s and 100s?  Being a
> > power plant operator I would say quite a bit although I am rethinking
> that
> > some due to the way the turbines push and pull each other.  I can
> envision
> > some fine whole grid oscillations due to that push and pull.
> >
> > bill
> >
> >
> > On Mon, Nov 18, 2013 at 4:15 PM, Tom Van Baak <tvb at leapsecond.com>
> wrote:
> >
> >> Magnus,
> >>
> >> I'm going to push back a bit on your mains sampling claim. Mostly, I'd
> >> like to see the results of the professional I-Q demodulated gear that
> you
> >> mentioned. Can you post raw data, or a sample plot?
> >>
> >> I agree that looking at power line voltage with 16- or 24-bits at 1 Msps
> >> is going to reveal interesting amplitude and phase noise information.
> But
> >> see how well a $1 PIC can do.
> >>
> >> Attached is a plot made using TimeLab + picPET just now. The picPET is
> >> fast enough to capture the zero-crossing of every 60 Hz cycle with 400
> ns
> >> resolution; the TimeLab plots have tau0 of 16.67 ms.
> >>
> >> -- The blue trace was simply plugging a 9 VAC wall-wart into the picPET
> >> though a 10k resistor.
> >> -- The pink trace was adding a 10 nF cap across the input.
> >> -- The green trace was unplugging my laptop switching power supply from
> >> the same outlet!
> >> -- The red trace is replacing the mains wall-wart with a hp 33120A set
> to
> >> 9VAC at 60 Hz, a tentative noise floor measurement of the picPET when
> used
> >> this way.
> >>
> >> My conclusions are that at least here in the US, or at least at my
> house,
> >> the short-term stability of mains hits about 5e-6, at about tau 0.2
> >> seconds. The attached short-term plot is also not-inconsistent with the
> >> long-term plot at http://leapsecond.com/pages/mains/
> >>
> >> My other conclusion is that the picPET (a simple PIC-based time-stamping
> >> counter) is doing a pretty good job measuring this. Note, no software or
> >> data filtering was used. This is just raw serial/USB data going into
> >> TimeLab.
> >>
> >> /tvb
> >>
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> >>
> >
> >
> >
> > --
> > Doc
> >
> > Bill Dailey
> > KXØO
> > _______________________________________________
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-- 
Doc

Bill Dailey
KXØO