aaron_do
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Hi,
short answers, 1) yes, 2) no.
The thing is that bandwidth is a measure of how much of the frequency spectrum a signal occupies. Basically I think Ken was implying that it is a scalar quantity, so you're using the wrong terminology. I simply assumed that you were talking about the spectrum of a baseband signal.
The signal is contained in two channels, the in-phase channel, I, and the quadrature-phase channel, Q. For transmission, the I channel modulates one phase of the RF carrier, and the Q channel modulates a 90 degree phase shifted version of the carrier, and the two are summed together. For the purposes of mathematical manipulation, I believe that you can represent the two channels as real and imaginary parts.
Again, "bandwidth" is not transformed, the signal itself can be represented as a magnitude, A(f), and a phase, θ(f). The I-channel by itself is symmetrical both in magnitude and phase about zero frequency (phase might have rotational symmetry, I can't remember and I'm lazy to check). The Q channel by itself is also symmetric both in magnitude and phase. The combination I+jQ is NOT symmetric either in magnitude or phase. However, there is no part of the physical design where the signal I+jQ can be represented by a single voltage. It is just a mathematical representation and not physical. I and Q are not combined until they modulate a carrier. The modulated carrier is a real, physical signal, and it's spectrum is symmetric both in magnitude and phase.
best regards, Aaron
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