[time-nuts] Ultra low phase noise floor measurement system for RF devices.

[SAIDJACK at aol.com]

In a message dated 3/31/2007 17:29:21 Pacific Daylight Time,  
bruce.griffiths at xtra.co.nz writes:


Multiplying the 2 signals is essential as the non correlated  components 
of the 2 signals will then average to zero (for infinite  measurement 
time) whilst the correlated components of the 2 signals will  not.
A cross spectral analysis is somewhat analogous to using an array of  
single frequency correlators. The residual noise decreases as the  
integration time increases. When multiple power spectra are averaged the  
noise floor will decrease as 1/n where n is the number spectra  averaged.

Bruce


Hi Bruce,
 
got it, thanks.
 
But isn't a signal source typically single-ended, and has a 50 Ohm source  
impedance which creates noise?
 
Wouldn't we need a source with 1 Ohm source impedance even if the  
measurement system is cross-correlated?
 
Would a differential source suffice?
 
bye,
Said



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