User:Alinja/sandbox

QAM tx signal is defined as:


 * $$ s(t) = I(t) \sin (\omega t) + Q(t) \cos (\omega t)$$

demodulated by multiplying with sin wt:


 * $$ r(t) = s(t) \sin (\omega t) = I(t) \sin (\omega t)\sin (\omega t) + Q(t) \cos (\omega t)\sin (\omega t)$$


 * $$ = \frac{1}{2} I(t) (1 + \cos (2 \omega t)) + \frac{1}{2} Q(t) \sin (2 \omega t)$$


 * $$ = \frac{1}{2} I(t) + \frac{1}{2} (I(t) \cos (2 \omega t) + Q(t) \sin (2 \omega t))$$

where everything but the first term is removed by simple low pass filtering. Thus only the original modulating I(t) signal is left and Q(t) doesnt affect it.

simple? Q(t) can be demodulated by muliplying with cos wt.