it may be a stupid question but while learning about DSP and Modulation I was wondering, if the I/Q representation of an RF Signal is of any use, when the received signal does not contain any modulation. So I understand the concepts of Inphase and Quadrature components, how they are modulated in the sender, combined for transmission and demodulated in the receiver. But if i where to receive some other signal, lets say for example RF-emissions from some random or physical source i want to observe. Does the separation into I- and Q components yield any value then? Since it has never been composed to hold information by the source. Or would there still be a value in having I- and Q components?

I couldnt find any explicit statement on that yet.




1 Answer 1


If you are "observing" the source, this implies there is some sort of information you are looking to get out of it, whether it be the total background noise, interference levels etc.

Do you find "value and use" in the RF signal's magnitude versus time? What about the RF signal's phase versus time? The IQ representation gives us both of these and it simply is another way to represent complex numbers:

$$Ae^{j\theta} = A\cos(\theta)+jA\sin(\theta) = I + jQ$$

One reason complex numbers (I/Q representation) for RF signals are useful is that for real signals, the positive and negative frequency spectrums are complex conjugate symmetric as complex numbers. This means we can represent any real RF signal using just the positive (or negative) spectrum as an analytic baseband signal, describing the signal independently from the carrier frequency.


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