[time-nuts] On some pitfalls of the dual mixer timedifferencemethod of h...

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Oct 7 22:59:36 EDT 2006

Tom Van Baak wrote:
>> Interesting as the techniques employed may be, the resultant performance 
>> is still inadequate for characterising state of the art oscillators.
>> The instrument phase noise floor is higher than that specified for 
>> current low noise (but not necessarily low drift) crystal oscillators.
> Well, true, but perhaps one definition of "state of the art"
> is simply when the high-end test tools that you can buy
> off the shelf are inadequate compared to the newest
> technology you are building in the lab...
> /tvb
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My point really was that "inferior" analog techniques such as 2 
reference source 2 mixer cross correlation analysers have a phase noise 
floor 15-20dB lower than the supposed superior direct digital mixing 
techniques. Such cross correlation instruments are commercially 
available from Wenzel associates and others.
The latest Agilent phase noise analysers use analog mixers, dual digital 
phase locked loops and digital cross correlation.


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