Q=Quadrature, I=In-phase (As you point out not in the first couple pages, but waaay down) he "explains" those https://wirelesspi.com/two-birds-with-one-tone-

Q=Quadrature, I=In-phase (As you point out not in the first couple pages, but waaay down) he "explains" those https://wirelesspi.com/two-birds-with-one-tone-i-q-signals-and-fourier-transform-part-1/#:~:text=What%20are,Signals%3F https://wirelesspi.com/two-birds-with-one-tone-i-q-signals-a... Not trying to be charitable like furgot ... The wikipedia page is the first time I've seen authors go pro on the topic