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

[Jürgen Appel]

Hej, 

On Monday, 29 November 2021 04:29:58 CET Matt Huszagh wrote:

> I've got a 10 MHz distribution amplifier and am considering purchasing a
> 5 MHz reference. Most (not all) of my equipment accepts a 5 MHz
> reference, but I'd like to be able to use the existing distribution
> amplifier I have if possible. Therefore, I'm considering ways I might
> generate a low-noise 10 MHz signal from the 5 MHz reference.
> 
> An obvious way is to use a doubler. However, as I understand it, even an
> ideal doubler will add 20log(2)=6 dB of phase noise to the 10 MHz
> signal. 

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.

Cheers,
	Jürgen