[time-nuts] Do time nuts only use and measure 10MHz clocks?

[cdelect at juno.com]

Erik,

Coherence is not the issue.

Sampling at the same time (coincidence) is!

For instance with a 1Hz offset if you have 5Mhz Ref and 5.00000000001 DUT
Your TIC will read close to zero if they are near coincidence. It they
are at the limit just before wrapping you will read close to full scale
.999999999.

The offset oscillator noise only gets cancelled at near to zero
coincidence. The further away the more offset oscillator noise affects
the measurement. You can use a really good oscillator for the offset
oscillator and that will help. I use an FTS 1200.

To see these effects take a look at this post.
Go down to the 16th and 17th from the top for some realtime results
showing this effect.

https://www.eevblog.com/forum/metrology/dmtd-tutorial/

In my first DMTD system
https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nbsir75-827.pdf

There is a variable phase shifter in one channel to allow adjusting to
coincidence.

However it's easier for me to adjust the REF or DUT slightly until
coincidence is achieved and  the frequencies are close enough so that the
measurement counts are stable or drifting very slowly.

Cheers,

Corby