Interest of IQ (QAM) processing at receiver level

[Ravaner]

Hello.

My question is about a specific case. Assume emitted signal ihas not been created using IQ modulation, what is the interest to rebuild an IQ signal in receiver before port-processing ?

 

[berkeman]

has not been created using IQ modulation

How do you generate a QAM signal without using modulated I and Q generation stages?

 

[Tom.G]

Look at: https://witestlab.poly.edu/blog/capture-and-decode-fm-radio/

 

[f95toli]

Hello.

My question is about a specific case. Assume emitted signal ihas not been created using IQ modulation, what is the interest to rebuild an IQ signal in receiver before port-processing ?

Well, the obvious reason would be that you are interested in both the amplitude AND phase of the signal.
IQ demodulation is used for all sorts of things in MW engineering; not just for QAM and other modulation schemes.

 

[Ravaner]

Thanks for your replies

 

[tech99]

Thanks for your replies

If we demodulate the signal using a local carrier, IQ demodulation enables frequencies one side of the local carrier to be rejected, providing image rejection or single sideband reception.

 

[Baluncore]

By employing an I/Q local oscillator, with two mixers, you can perform image rejection and convert one RF signal into two IF signals, I_if and Q_if. Those two IFs can be synchronously digitised to generate data pairs that are phasors with two A-D converters, at half the rate needed for a single RF channel. In effect it doubles the BW of the best AtoD converters available.

So I think the answer to your question is that it enables image rejection and permits a wider bandwidth conversion.

See; RF Down Converting to I/Q Data. http://whiteboard.ping.se/SDR/IQ