[time-nuts] Re: Lowest noise (phase noise and ADEV) method to achieve 10 MHz signal from 5 MHz input

[Matt Huszagh]

Jürgen Appel <jap at dfm.dk> writes:

> Yes, this is a fundamental physical property which cannot be avoided.  
>
> You can see it that way: If there is a given fluctuating time delay in your 
> otherwise perfect 5 MHz signal, the amount of phase shift this time 
> fluctuation corresponds to in a 10 MHz signal is simply twice as big as in the 
> 5 MHz signal, simply because the phase evolves twice as fast at 10 MHz.
>
> This factor of two makes up the 6dB in noise power.
>
> If you divide the 6 dB noisier 10 MHz signal down again, (neglecting 
> additional technical noise), you get the original performance of your 5 MHz 
> signal back.

Doesn't this assume that you inherit all the noise of the reference? For
example, the short-term stability of a GPS 1PPS signal is poor, but you
can still use it to discipline a VCO with much better short-term
stability and retain most of the short-term stability of the VCO.

Matt