Radio Waves

The radio wave that leaves a transmitting antenna originates as a sound spoken into a microphone. A microphone is a device for converting sound energy into electrical energy. A microphone accomplishes this transformation by any one of a number of mechanisms. In a carbon microphone, for example, sound waves entering the device cause a box containing carbon granules to vibrate. The vibrating carbon granules, in turn, cause a change in electrical resistance within the carbon box to vary, resulting in the production of an electrical current of varying strength.

A crystal microphone makes use of the piezoelectric effect, the production of a tiny electric current caused by the deformation of the crystal in the microphone. The magnitude of the current produced corresponds to the magnitude of the sound wave entering the microphone.

The electric current produced within the microphone then passes into an amplifier where the current strength is greatly increased. The current is then transmitted to an antenna, where the varying electrical field associated with the current initiates an electromagnetic wave in the air around the antenna. It is this radio wave that is then propagated through space by one of the mechanisms described above.

A radio wave can be detected by a mechanism that is essentially the reverse of the process described here. The wave is intercepted by the antenna, which converts the wave into an electrical signal that is transmitted to a radio or television set. Within the radio or television set, the electrical signal is converted to a sound wave that can be broadcast through speakers.