The discussion centers around the concept of measuring quadratures in relation to homodyne detection, exploring its implications in various signal types, including radio and optical signals. Participants seek to clarify the definitions and significance of amplitude and phase in this context.
Participants express varying interpretations of amplitude and phase, indicating that there is no consensus on the definitions or implications across different signal types. The discussion remains unresolved regarding the specific meanings and applications of these concepts.
Participants do not fully clarify the assumptions underlying their definitions of amplitude and phase, nor do they resolve the differences in interpretation based on signal type.
f95toli said:It simply means measuring the cos phi and sin phi (or equivalenty the real and imaginary parts if you prefer complex notation) terms of the signal.
From which it follows that if you represent the signal using phasors, the quadratures (I and Q) correspond to the x and y axis, respectivly,
One obvious reason for measuring the quadratures is that you get BOTH the amplitude and the phase iof the signal, whereas "normal" homodyne detection will only give you the intensity.
In order to measure both quadratures in the MW regime you need a couple of mixers and a 90 degree phase shifter (in reality this will be a hybrid) or simply and IQ-demodulator.
If you are working at lower frequecies an ordinary lock-in amplifier will work (the "X" and "Y" outputs) .