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Radio Broadcast
An aerial wire connected to a receiving set constitutes an electric path of definite length for these electrons to move back and forth upon. It takes them a certain time to rush from one end of this path to the other and back again. If the surges are coming through the ether from the transmitting station at just the proper frequency to push these electrons on their happy way back and forth on the rises and falls of the radio waves, the maximum commotion will be produced in the receiving set. The process of tuning adjusts the length of this path to make the time of travel just right for the particular radio waves desired. So, when the tuning is correct, the electrons will rush back and forth with the incoming waves.
PRODUCING SOUND BY ELECTRICITY
AT THE sending station, sounds in the air are controlling the output of the radio transmitter. A mouthpiece is arranged to pick up the sound waves. These waves are much slower in their number of vibrations per second than radio-frequency waves which are being sent out into space. But the mouthpiece is connected to the radio transmitter in such a manner that the air pressures of the sound waves striking the mouthpiece will con
trol the intensity of the radio waves transmitted. As a result the million or so n waves per second will leave the transmitting station, but their intensity or power will vary up and down in step with the sound waves which strike the mouthpiece.
In consequence, the electrons in each of the receiving stations will move back and forth most rapidly in step with the incoming radio waves, but the intensity or force of their motion will vary depending upon the variable intensity of the incoming radio waves. As a result of this, the intensity of their motion will correspond to the sound vibrations at the transmitting station. To discover these changes in intensity and translate them into sound is the function of the receiving set.
HOW THE TELEPHONE RECEIVER WORKS
THE most practical device so far developed for changing electric effects into sound is the telephone receiver invented by the late Alexander Graham Bell. In this, electric currents of the same frequency as the desired sound, vibrate in the electric coils and in so doing pull the thin iron diaphragm of the receiver back and forth, pushing and pulling the air around the receiver to correspond, and in consequence
A
KING ELECTRON HOLDS THE TURNSTILE
On the dip in the radio-wave, the accommodating electrons rush back from the ground at C, through the tuner coil to B, to the tuning condenser and out to the antenna at A. This change of affairs makes those in the alternate crystal-detector route around through F, H, E, and D to B want to return; but the turnstile action of the crystal detector prevents them, and the trapped electrons at H have nothing left to do but continue around through the telephone receiver and out through G. The result is that the activity of the electrons urged on by the radio waves shows itself by a continued action in cue direction through the telephone receiver, moving the receiver diaphragm and making sound.