Wireless Telegraphy and Telephony

 WIRELESS TELEGRAPHY 55 direction but not permitting it to pass in an opposite one. The high frequency oscillating currents may be represented by a curved line crossing and recrossing a zero line and gradually decreasing in amplitude as shown by A in Fig. 66. The detector, acting as a valve, eliminates one half of the alternating current so that the result may be repre- sented by B, in reality a pulsating direct current which rises and falls but is able to flow through the telephone receiver and produce a motion of the diaphragm with consequent sound waves audible to the ear. Fig. 68.—Diagram drawing analogy between rectifying action of a detector and a pump. The accompanying sketches and the following analogy drawn between the electric currents and the flow of a stream of water may serve to render a better conception of how it is possible for the valve action of a detector to rectify an alternating flow, continuously reversing its di- rection to an intermittent current passing in one direction only. The illustration shows two pumps A and B. Each pump is immersed in a pool of water and consists of a cylindrical tube T and T' having a small opening, O and O', at the lower end to admit the water and a piston, P and P', operating up and down inside the tube. Every time