Post subject: Mixer SSB and DSB conversion loss and NF
postPosted: Fri Dec 24, 2004 5:22 pm
I read in
an application note that there is a difference of 3dB between SSB noise
figure and conversion loss of a mixer to these paramaters in DSB (conversion
loss of SSB is 3dB higher than DSB).
If you input DSB (Dual Side
Band) signal with twice as power as SSB signal to a given mixer you
will obtain twice as power at the output as well. And if you input the
SSB signal to that mixer the ratio of power in the input and output
should remain the same (only with 3dB less in the aboslute values at
each port) - please correct me if I am wrong!
My question is
why is this difference?
Post subject: Mixer Noise Figure
Mon Dec 27, 2004 2:36 pm
The double side band has twice the
power level , therfore the signal to noise ratio at the output is 3dB
higher. In a SSB mixer, half the power is at the output, but the same
noise power. The signal to noise ratio is 3dB lower. Therefore, the
noise figure is 3dB higher.