[time-nuts] Crosscorrelation phase noise measurements

Magnus Danielson magnus at rubidium.dyndns.org
Thu Aug 2 23:31:41 UTC 2012

Hi Sylvain,

On 08/02/2012 11:24 PM, Sylvain Munaut wrote:
> Hi Magnus,
> Thanks a lot for the concise and very clean explanation.

You are welcome!

> The cross-correlation part between the two signal was clear enough in
> my head but I didn't really see how it would achieve much gain. I
> didn't think about averaging many resulting spectrum while they're
> still complex (and not just the amplitudes ... ). I assume that the
> cross correlation of the two measurement makes the phase of several
> consecutive measurement "align" so that the main signal accumulates
> over many averages while the noise is just averaged out.

Because they correlate, they add up, because the noise does not 
correlate, it flattens out.

You should look up what is written by NIST on this technique. They have 
a nice online archive.

They also demoed it on the NIST seminar.


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