[time-nuts] accurate 60 hz reference chips/ckts

[Tom Van Baak]

Jim,

> You would want a filter time constant of several hours in the control loop
> to smooth out the variations in the 60 Hz.

One can determine the appropriate time constant by looking at the ADEV of the two clocks [1].

For GPS and OCXO the choice of time constant is fairly obvious. But the ADEV for mains frequency isn't quite as pretty. So I'm not sure several hours would work; maybe more like days or weeks? Here's a sample ADEV for power line frequency:

http://leapsecond.com/pic/mains-adev-mdev-gnuplot-g4.png

I'd be curious if anyone has tried a mains disciplined oscillator and how well it performed. Unlike a GPSDO, absolute phase can be lost (e.g., power fail) so maybe use FLL instead of PLL. Shall we call it MFDO (mains frequency disciplined oscillator)?

Hal and I have months, even years, or mains zero crossing timestamps so if someone wants to simulate how well a MFDO might work let us know. Maybe just adapt the gpsdo simulator [2].

/tvb

[1] some examples:
www.thinksrs.com/assets/instr/PRS10/PRS10diag2LG.gif
www.thinksrs.com/assets/instr/FS740/FS740_unlockedLG.gif
www.thinksrs.com/assets/instr/FS740/FS740_lockedLG.gif
www.leapsecond.com/pages/gpsdo

[2] gpsdo simulator project
http://www.leapsecond.com/pages/gpsdo-sim/

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