Radar is an electronic system that permits man to see objects at great distances regardless of darkness or bad weather. It is used to direct both air and sea traffic, and for detection and identification of unknown ships and aircraft.
   Sound waves bouncing off hillsides or tunnel walls create an echo. Radar works in the same way by sending out short pulses of radio energy which bounce off objects in their path and return to the sender as a type of echo. The reflected impulses are shown on a screen, like that of a television set, as spots of light, or blips.
   Most radar sets have six important parts: the modulator, which turns the transmitter on to send a pulse and off to receive an echo; the transmitter, which sends the very short, or microwave, pulses; the antenna, which focuses the pulses into a narrow beam and also receives the echoing signals; the duplexer, which, as a switching device, connects first the transmitter and then the receiver to the antenna; the receiver, which is a listening and amplifying device to strengthen weak echoes so that they will show on the radar screen; and the indica­tor, which displays the blips to the operator on its screen.