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

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri Mar 30 23:14:40 UTC 2007


Mike Feher wrote:
> Well, I must admit I did not read the referenced article, but, he is talking
> about dBc, or relative to the carrier and not kT. So, if the carrier power
> is high enough I suppose it could be done. Even suppose you could measure
> it, what would it take to generate such a pure carrier. That may even be
> more difficult. - 
>
>  
>  
> Mike B. Feher, N4FS
> 89 Arnold Blvd.
> Howell, NJ, 07731
> 732-886-5960
>   
Mike

 It actually measures the additive phase noise of  components 
(amplifiers, splitters, transformers etc.).
Since it uses a cross correlation technique it can easily achieve a 
noise floor below the thermal noise.
Cancellation of the carrier in the interferometer/bridge allows use of a 
source with a phase noise well above that of the measurement system.

In is possible to build lower phase noise oscillators using very low 
phase noise sustaining amplifiers.
Such amplifiers can be implemented using feedforward correction techniques.
An RF bridge/interferometer is used to null the carrier at the input to 
the low noise figure correction amplifier, so that only the phase noise 
and other error components produced by the main amplifier are seen by 
the correction amplifier the output of which is combined with (correct 
delay and gain) the output of the main amplifier to reduce the composite 
amplifier phase noise. Phase noise is absent when a carrier is not 
present, so the phase noise contribution of the correction amplifier 
will be very small if the interferometer/bridge is well balanced. This 
technique has been used to reduce the phase noise of microwave 
oscillators. In principle there's no reason it cannot be used at lower 
frequencies.

Bruce




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