Radar equipment used in ships, aircraft, and airfield control towers employs pulses of very short radio waves, for the purpose of finding the distances from the transmitter of various objects, e.g., coastline and building outlines together with other ships or
aircraft. A rotating (scanning) aerial sends out a series of high-frequency radio pulses which are received back as echoes from the objects on which they fall. The time interval between transmission and reception of the pulse depends on the distance of the reflecting object. These signals are used to produce a picture of the area scanned on the screen of a special cathode ray tube (Fig. 26.22). One form of cathode ray tube is described- in chapter 44.