How Radio Communication Works

Sound and radio waves are different phenomena. Sound consists of pressure variations in matter, such as air or water. Sound will not travel through a vacuum. Radio waves, like visible light, infrared, ultraviolet, X-rays and gamma rays, are electromagnetic waves that do travel through a vacuum. When you turn on a radio you hear sounds because the transmitter at the radio station has converted the sound waves into electromagnetic waves, which are then encoded onto an electromagnetic wave in the radio frequency range (generally in the range of 500-1600 kHz for AM stations, or 86-107 MHz for FM stations). Radio electromagnetic waves are used because they can travel very large distances through the atmosphere without being greatly attenuated due to scattering or absorption. Your radio receives the radio waves, decodes this information, and uses a speaker to change it back into a sound wave. An animated gif of this process is given below.

A sound wave is produced with a frequency of 5 Hz - 20 kHz. NEXT	The sound wave is equivalent to a pressure wave traveling through the air.	A microphone converts the sound wave into an electrical signal. NEXT	The electrical wave traveling through the microphone wire is analogous to the original sound wave. NEXT
The electrical wave is used to encode or modulate a high-frequency "carrier" radio wave. The carrier wave itself does not include any of the sound information until it has been modulated. NEXT
Your radio contains an antenna to detect the transmitted signal, a tuner to pick out the desired frequency, a demodulator to extract the original sound wave from the transmitted signal, and an amplifier which sends the signal to the speakers. The speakers convert the electrical signal into physical vibrations (sound).		The signal is transmitted by a radio broadcast tower. NEXT	The carrier wave can either be amplitude modulated (AM, above) by the electrical signal, or frequency modulated (FM, below).

The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.