[time-nuts] Mains frequency

[Charles Steinmetz]

Chuck wrote:

>In the case of a 60Hz mains derived signal, most of the noise is
>going to be riding on the signal, and will be amplified with your
>gain stage.

The potential evils of bandpass filters in a timing chain are well 
known, but as long as you can accept the delay of a filter (or 
correct for it, which should be trivial with a PIC or other uC), you 
may be much further ahead with a noisy signal like the AC mains if 
you use a sharp bandpass filter on the incoming 60 Hz then amplify & 
clip the signal to increase the slew rate.  Active filters with fast, 
quiet op-amps should do the job well.  For the lowest jitter, a 
Collins-style multi-stage zero cross detector may be helpful.

Best regards,

Charles