Nowadays, you get a (sizable) glimpse of it in 6.02, which is usually taken before 6.003 (in fact, it is a prerequisite), and which deals with digital communica

Nowadays, you get a (sizable) glimpse of it in 6.02, which is usually taken before 6.003 (in fact, it is a prerequisite), and which deals with digital communication systems. Perhaps 6.002 also presents pieces of Fourier stuff when needed.