To illustrate how confusing and muddy it can get, the RS white paper in the following link states that the two tones at f1 and f2 of frequency apart delta_f (=f2-f1) will produce 3rd order IMD products at f1-delta _f and f1+delta_f. What the heck? Everywhere i have seen the 3rd order IMD should be at 2f1-f2 and 2f2-f1(attached):
https://scdn.rohde-schwarz.com/ur/pw...Distortion.pdf
Digging deeper, i get more nasty surprise, constellation diagram, IM interference etc. It is like opening the Russian Matryoshka Nesting Dolls, there are more Maths, abstraction and complications every time I unravel the inside, frying my brain.