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

[Erik Kaashoek]

Corby,
Thanks for the links.
The tinyDMTD I'm using does not use a TIC after the mixer to measure 
zero crossing but samples the whole output of the mixers and measures 
the phase by I/Q down converting to zero Hz and calculating the phase of 
the complex signal.
Previously (earlier version of the tinyDMTD) I use two signals at 10MHz 
and 0.01Hz apart, measured the phase over a 310 s period to check if the 
phase difference of the input signals had an impact
see: http://athome.kaashoek.com/time-nuts/DMTD/Phase_difference.png
and calculated the unwrapped linear residue
see: http://athome.kaashoek.com/time-nuts/DMTD/Phase_difference_residue.png
As you can see the maximum phase error due to pulling is +/- 60 ps
The ADEV confirms the offset oscillator noise is canceled out 
independent of phase difference as the ADEV of this oscillator at tau = 
1 s is very bad (around 1e-10) and the measured ADEV at tau = 1 s is 1e-12
see: http://athome.kaashoek.com/time-nuts/DMTD/Phase_difference_ADEV.png
Erik

On 9-10-2022 18:01, Corby Dawson via time-nuts wrote:
> Erik,
>
> Coherence is not the issue.
>
> Sampling at the same time (coincidence) is!
>
> ... snip ...
> The offset oscillator noise only gets cancelled at near to zero
> coincidence. The further away the more offset oscillator noise affects
> the measurement.