Hi Rfcooltools
Quote:Passive mixers suffer from being bidirectional and the noise at baseband will get mixed up to RF as a double sideband noise per I or Q and then get remixed down on the opposite quadrature and this
Can you explain why it gets remixed to the opposite quadrature?
Your observation is very original and most interesting, i want to say. I thought a little bit on this and came to the following conclusion (which could be faulty) - the baseband noise(or signal) gets upconverted to RF and then downconverted to baseband; the downconverted noise again gets upconverted and downconverted - this process goes on indefinitely.
If i represent Q as the baseband signal and assume a conversion gain of -3dB for both upconversion and downconversion, at the first downconversion, the baseband signal increases by Q/4, the second downconversion Q/16 and so on (there would be some phase shift as well)
Adding all the signals (ignoring phase shifts) up we get
Q+ Q/4 +Q/16 + Q/64 .. a converging infinite series that sums to
Q.4/3