Back when I was a CATV tech, we used a sweep generator and spectrum analyzer to test the system's frequency response every six months. I remember because I'd have to start at 03:00 and stop the sweep generator at the head end by 07:00 or else people would call the office to complain about the repeating blip that ran through the picture while it was running. Hell hath no fury like someone pissed off about the quality of their TV reception.