[time-nuts] Mains frequency

[Bill Dailey]

ok Bob,

Then how do you tease out the difference between the clean generated 60Hz
and the mains 60Hz adev curves to determine what is noise and what is the
variability in the 60Hz?  That is the point of my question not semantics
about ideal vs non-ideal.

doc


On Mon, Nov 18, 2013 at 8:36 PM, Bob Camp <lists at rtty.us> wrote:

> Hi
>
> There is no way to come up with the noise floor of the picPET from that
> plot. In fact coming up with the floor of a single channel device like the
> picPET is not all that easy. First you need an ideal noise free sine wave
> signal …. I’ve spent more than a few hours on that particular project with
> other list members involved as well. As always we kept it off list to keep
> from offending those who place a high value on their bandwidth.
>
> Bob
>
> On Nov 18, 2013, at 9:11 PM, Bill Dailey <docdailey at gmail.com> wrote:
>
> > 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
> >>> _______________________________________________
> >>> time-nuts mailing list -- time-nuts at febo.com
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> >>
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> >
> >
> >
> > --
> > Doc
> >
> > Bill Dailey
> > KXØO
> > _______________________________________________
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-- 
Doc

Bill Dailey
KXØO