[time-nuts] Mains frequency

[Didier Juges]

Tom,

Don't confuse everybody with facts, we had a good thread going :)

The PicPet is holding its own very well in that application.

I am surprised at the effect of the laptop supply. I would have certainly expected effect on phase noise (smaller taus), but not that close to the carrier. Do you know if it is a power factor corrected supply or not?

Didier KO4BB


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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