Get I and Q components from a signal (multple frequency signal)? Is there anyway to get the I and Q components from a signal in the time domain? The signal has multiple frequencies.

So far I have been doing this in a SIMPLE situation:


Fast fourier transform to get each frequency and each frequencies amplitude and phase 
Then use $\cos(\textrm{phase}) \cos(2 \pi f \times \textrm{time_vector}) -
   \sin(\textrm{phase}) \sin(2 \pi f \times \textrm{time_vector})$ for each frequency.
This gives me I and Q data for each frequency, then I just need to
sum them to getback the original signal.


Problem is, I am trying to do something more complex and need to get the I and Q data straight from the time domain signal without following the above steps. Where I is In phase component &amp; Q is Quadrature phase component of the signal.
If you need to do it in time domain you need an ideal Hilbert transform filter and multiply it sine function, and pass it through low pass filter (lpf)to get Quadrature (Q) phase. but don't expect accurate results, or maybe you can use PLL but you have to use it brilliantly like below.