[time-nuts] Question about precise frequency / phase measurement

[Azelio Boriani]

Yes, and, as you can see, you have to wait 1 hour.

On Thu, Apr 19, 2012 at 9:49 PM, <SAIDJACK at aol.com> wrote:

> Hi Wolfgang,
>
> one of the easiest and very accurate ways to do this is simply to measure
> the drift of the two 10MHz signals on an oscilloscope. Adjust the OCXO so
> that this drift between the two traces is as slow as you can get it. Then
> simply  measure it over time. Use one signal for trigger, the other to
> display
> if  you only have a one channel scope.
>
> If you get say 10ns drift over 1 hour (which you can easily measure even
> with the cheapest scopes), that is a resolution of 10ns/3600s = 2.78E012.
>
> Or in other words 27.7uHz!
>
> This has been discussed before and documented in the time nuts archives
> some time ago.
>
> bye,
> Said
>
>
>
>
> In a message dated 4/19/2012 12:10:53 Pacific Daylight Time,
> skywatcher at web.de writes:
>
> My first  approach was to use a simple XOR phase comparator. I tried a
> 74HCT86 and a  74HCT4046.
> It works, but it's very noisy, so i don't get better than about  10 mHz
> frequency resolution.
> If i look at the lowpass-filtered output i  don't see a nice sine or
> triangular wave, but it looks more
> than a  triangular wave with round tops and some bumps between them.
> Another  problem is that the
> difference frequency gets very low when the frequencies  are very close,
> so it's not enough to look
> only for zero crossings of  the difference signal.
>
> Does anybody know a possibility to get a  resolution < 1 mHz ?
>
> Best regards,
> Wolfgang
>
>
>
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