I've spent many hours reading and doing research about this. I don't attend any university classes or any type of classes that may approach such a topic. I am trying to learn this by my own without any help what so ever. So please understand if I say something inaccurate or if I'm asking an obvious question. I have been studying quadrature because I need it to develop in software defined radio platforms. The problem is that I have found a lot of contradictory information.
Let's start from the beginning. Given a real signal to a quadrature circuit, two components are generated,
I, the real component, and
Q, the imaginary component, which is the same as
I, only it has a
90º phase shift. So, we have
Q, which are the same signal but
90º shifted from each other. I understand this, it's simple.
Now let's see an example. Have a look at this paper about QAM on ni. I read the paper and I understood it. The problem that is if you take a look at the baseband graph, the
Q components are completely different. They shouldn't, right? They should be equal to each other apart from the
90º phase shift. At least that is what I understood after reading many papers and articles on the subject.
Now let's take a look to this article about IQ on tek. Having a look at the last two images, I can visualize what's happening. The
Q are being transmitted and then received. I can see that the
Q components transmitted are the same being received. What I don't understand is that
Q isn't by any means equal to
I with a
90º phase shift. That is what's supposed to happen right? Maybe not? I can't seem to understand it. I know that the
I is obtained by multiplying the real signal by
2cos(w(c)t) and that
Q is obtained by multiplying the real signal by
-2sin(w(c)t). So, what I saw before clearly makes no sense.
Again, I'm sorry for my ignorance in the subject but I am doing my best trying to understand this. I'm just confused by this contradictions. Thanks in advance for anyone who tries to explain this to me, really.