[time-nuts] Mains frequency

[Tom Van Baak]

> Again, why are you measuring the AC line?  I'd think maybe to measure the
> noise that is on it.  The fundamental freq. changes second by second.
> It's not a clean 60Hz my any means.  The rate of frequency change is one
> thing you'd like to measure
> 
> I was just watching a minute ago and can see a 0.01Hz/second drift.  It is
> likely MUCH worse as what I was watching is filtered over second

Chris,

No, forget the noise (it's actually quite clean: look at it sometime).

We measure mains because we can.

We also measure it because millions of wall-clocks are based on mains frequency; it was the original "GPSDO".

We measure it because its phase plot, frequency histogram, and ADEV plot are really quite interesting.

We measure it because Seattle, WA (tvb) and New Mexico (Kevin) are both on the same grid and mutually agree to 10 microseconds (!) over an hour even though they can both wander by many seconds relative to UTC. It's a textbook example of common view time transfer. See also:
http://leapsecond.com/pages/mains/
http://leapsecond.com/pages/ac-detect/

You too can join the mains party. Measure it with your own method, or a fancy TrueTime time/frequency deviation meter (TFDM) or use something simple like a picPET (http://www.leapsecond.com/pic/picpet.htm) or Arduino or even a NTP/Linux/serial DCD pin hack.

/tvb