This is a bit of a basic question, but I am having trouble understanding why a signal needs to be broken up into I and Q components to be useful for software-defined radio (SDR).
I understand that the I and Q components are the same signal, just 90 degrees out of phase, but I don't understand why this is important. Why can't you just digitise one signal? Why do you need an apparently identical signal that's out of phase by 90 degrees? And if you do need this second signal, why can't you create it yourself (e.g. in software) by just delaying the first signal?
All I can make out is that it's needed for some reason to do FM-style demodulation in software, but I can't find anything anywhere to explain what the need is, and why this demodulation is not possible without both I and Q components.
Is anyone able to shed some light on this? Wikipedia isn't particularly helpful, with each page having a link in lieu of an explanation, and each link pointing to the next in an endless loop.
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