Re: LO Phase Noise and wideband front ends

John G3UUT <yahoo@...>
 

Chris,
Are you sure that amplifier noise is AM noise? I always thought that amplified thermal noise, which this is, was an equal mix of both AM and PM noise.
73 John G3UUT

On 14/06/2016 08:54, Christopher Bartram cbartram@... [ukmicrowaves] wrote:
 

I haven't seen the original post on this , but, I suspect that the
problem isn't Phase Noise. For far too many people phase noise is a
pretty diffuse concept, and it gets blamed for a lot of effects for
which it's not responsible!

Phase noise is, in effect, a form of wideband frequency modulation, and
falls away quite quickly at 20dB/octave as you move away from the
carrier. What I believe, from reading Andy's post is that the problem is
amplitude domain noise (AM noise) caused by eg. amplifiers in the signal
path. This can have a pretty flat frequency/amplitude characteristic.

'Phase noise' gets the blame for many effects which are caused by AM
noise, and is a particular nuisance in wideband systems, but it behaves
differently to AM noise. Phase noise won't be cancelled in a balanced
mixer, but AM noise will be.

73

Chris
GW4DGU



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