Interest of IQ (QAM) processing at receiver level

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  • #1
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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 ?
 

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  • #2
berkeman
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has not been created using IQ modulation
How do you generate a QAM signal without using modulated I and Q generation stages?
 
  • #4
f95toli
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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.
 
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Thanks for your replies
 
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  • #6
tech99
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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.
 
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  • #7
Baluncore
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By employing an I/Q local oscillator, with two mixers, you can perform image rejection and convert one RF signal into two IF signals, Iif and Qif. 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
 
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