RADIO COMMUNICATION 



275 



Not this many radio vibrations are shown in Figure 127, but a 

 sufficient number are indicated to show how the change of 

 amplitude will impress on the high-frequency carrier wave the 

 lower-frequency sound vibrations. A crude analogy may help 

 to make this plain. If one drops a stone into a pond whose 

 surface is covered with little wind-made waves, the wave emanat- 

 ing from the point of the splash will be a resultant jointly of the 

 wind and the falling stone. The shore grasses, when the waves 



FIG. 127. Diagram of voice modulation of a continuous wave 



reach them, will not sway regularly as when only the wind 

 waves hit them, but irregularly, moved by the waves that also 

 bear the impress of the stone's disturbance. So the vibrations 

 of the human voice are carried along with the high-frequency 

 waves of the wireless telephone sender and register on the receiv- 

 ing apparatus. 



This change in current strength of the carrier wave, without 

 changing its frequency, may be accomplished by inserting a 

 microphone in the antenna circuit of the transmitting station. 

 This microphone is a telephone transmitter adapted for heavier 



