Radio broadcasting is an audio-based broadcasting service transmitted through the air, using radio waves from a transmitter to an antenna and on to a receiving device. According to the University of Memphis, ship-to-shore broadcasting was in use as early as 1910 but was being experimented with as early as 1897. The use of radio as a form of mass entertainment arrived in the U.S. in the 1930s, during the Depression. People looked to the radio for uplifting messages and escapist entertainment during the economic crisis. Theodore Roosevelt became known as the "first radio president" with his "fireside chat" addresses.
The first radio station to begin formal scheduled broadcasting was Westinghouse's KDKA-Pittsburgh, which broadcast the election returns on November 2, 1920, before continuing with a regular daily schedule of programs. In the U.K., the BBC broadcasting service was granted a royal charter in 1927, beginning a multi-station service still in operation today.
Amplitude Modulation (AM) was the earliest form of radio developed. This form of radio is still used around the world but is most popular in economically developing countries as the technology is simple. AM relies on the receiver to detect variations in the radio waves and amplify the signal through a speaker or earphones. Although AM stereo is possible, the majority of AM broadcasts around the world are mono.
Frequency Modulation (FM) occurs on VHF airwaves in the frequency range of 88 to 108 MHz. This radio band is commonly used in the developed countries such as the U.S. and Europe. It became popular because of the stereo recording techniques in the music recording industry. FM radio features higher sound fidelity and stereo broadcasting opportunities.
Digital Audio Broadcasting (DAB) was developed in the U.K. in 1995 and Germany in 1999 using the public domain Eureka 147 system. DAB remains most popular in Western Europe, Australia, South Africa, Asia and Canada. By 2006, over 1000 stations were broadcasting on this system, which was created to provide a higher quality of sound and allow a greater number of radio stations to operate.
This technology is most prominent in the U.S. and Canada, where two satellite radio services exist. XM Satellite Radio and Sirius Satellite Radio dominate the satellite radio of North America. Other companies have not entered the battle for satellite market share due to the high cost of space-based satellite technology and restrictions of availability on the radio spectrum.
Marconi's first radio transmission from the U.K. to Canada used Morse code; this system is still in operation today for sending coded messages. Radio broadcasts are also used by emergency services such as police, fire brigade and ambulance dispatch calls. Other frequencies are often used by commercial companies such as taxi services, which use radios to maintain contact with drivers.