[time-nuts] Mains frequency

[Chris Albertson]

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


On Sat, Nov 16, 2013 at 4:54 PM, Charles Steinmetz <csteinmetz at yandex.com>wrote:

> 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
>
>
>
>
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-- 

Chris Albertson
Redondo Beach, California