We’ve all experienced strong versus weak radio signals while driving a car and listening to the fm radio. The fading signal could be caused from traveling too far from the radio station transmitter, or from being blocked by hilly terrain or buildings. Lately I have been noticing something interesting while driving in city traffic with tall buildings around. When I have to slow down and come to a stop due to a red traffic light or something, I notice that the radio signal fades in and out every few meters. If there is a song playing that I like I will either stop a little short of where I normally would, in order to keep the signal strong, or if it dies in the spot where I stop, then I will ease forward just a little so that the signal gets stronger. When the light turns green and I start to move the signal comes in and out several times at regular intervals of a few meters. I know that this distance is in line with the wavelength of fm radio with frequencies from 88mhz to 108mhz, and I’m pretty sure that I am detecting radio wave diffraction patterns.