A Question about SSB and DSB Noise Figure.

dsb noise figure

Generally Speaking, to a mixer, its SSB Noise Figure is equal to DSB Noise Figure plus 3dB. This is because in SSB application, the signals of the mixer RF input at the image frequency band are restrained by the RF filter in front of the mixer, but the noise at that frequency band can still enter into the mixer.

But, this is different from Noise Figure measurement: In SSB Noise Figure measurement, the noise power from the Noise Source at the image frequency band is restrained by the RF filter. So in DSB Noise Figure measurement, the noise power from both bands can enter into the mixer. And the noise power at the image frequency band can be considered as the noise added by the mixer itself. So when we make Noise Figure measurement of a mixer or a receiver, if we have no filter in front of the mixer (this is called DSB measurement ), but we want to get the SSB Noise Figure, the SSB Noise Figure is equal to the DSB measurement result minus 3dB.
Of course, the 3dB difference between SSB and DSB is the ideal case.
Can anyone tell me whether it’s true or not?
Thanks.

double sideband noise figure

Hi,
I think that is true if the noise of Noise source and the noise of mixer of your downconversion system are the same at LSB and USB channels. See Agilent AP note 57-2 chapter 3.8.2 "Estimating SSB noise figure from
a DSB measurement"

Bye