A double-horn microwave emitter faces a microwave receiver. The receiver is also connected to a speaker, which displays the received signal as audio, and an oscilloscope, which displays the signal visually. When the receiver is moved perpendicularly to the emitter, constructive and destructive interference can be both seen and heard.When one of the emitter horns is covered, the interference pattern disappears.
Video from: techtv.mit.edu
