Which of these modes is most affected by non-linear phase response in a receiver IF filter?
A. Meteor Scatter
B. Single-Sideband voice
The answer is C. Digital. Why? Well, for one, the question is pretty vague. If you’re using a Frequency Shift Keying (FSK) digital signal you probably won’t have any problems. SSTV (D. Video) is a FSK mode. B. Single-Sideband Voice doesn’t particularly care about phase at all. And A. Meteor Scatter technically isn’t a “mode” at all, but rather a method of propagating the radio waves themselves.
However, if you are trying to transmit or decode a Phase Shift Keying (PSK) signal, then it only stands to reason that anything which alters that phase response in a way that is unexpected (like non-linear) will change encoding of the signal. The end result will probably be unreadable.