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

[Bob kb8tq]

Hi

At some point you must go “inside” the loop (or your OCXO isn’t locked …). At that
point, you run into the basic physics of frequency multiplication. 

Bob

> On Nov 30, 2021, at 7:16 PM, Matt Huszagh <huszaghmatt at gmail.com> wrote:
> 
> 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
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