[time-nuts] More 60 Hz graphs

[Poul-Henning Kamp]

In message <20110916001417.D49D3800037 at ip-64-139-1-69.sjc.megapath.net>, Hal Mu
rray writes:

>Here is the frequency:
>  http://www.megapathdsl.net/~hmurray/time-nuts/ppstest/60Hz-freq.png
>I don't know where the wobbles are coming from.  They might be in my 
>collection setup.

They are very likely resonance-effects in the power grid.  Power-grids
are not inherently stable things, and most of them have resonance
frequencies like that, depending on which generators run and what
the impedance are between them.

A few grids have operational SPICE-like models to warn them about
configurations which are unstable, but in general the thinking that
it would be possible to build an analytical model of the grid died
with decentral productions uptake a decade ago.

Try running a suitably windowed FFT on your data...

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.