American radio

Radio broadcasting in the United States is a major mass medium. Unlike radio in most other countries, American radio has historically relied primarily on commercial advertising sponsorship on for-profit stations. The U.S. does not have a national broadcaster that aims its programs at the general public. Nonprofit broadcasting typically comes in three forms: radio evangelism, community radio, and government-subsidized public radio, all of which rely at least to some extent on listener donations. Shortwave broadcasting in the United States includes federal government programs, as well as a limited number of privately managed broadcasts, for overseas audiences. Radio broadcasting became popular in the 1920s, alongside the new film industry. The arrival of television in the 1950s forced radio into a niche role, as leading participants moved into the much larger field of television. In the 21st century, radio has been adjusting to the arrival of the Internet and Internet radio.

In 1912, most amateur-radio transmissions were restricted to wavelengths below 200 meters (i.e., frequencies above 1500 kHz) to prevent interference to future commercial broadcasters. The beginning of regular, commercially licensed radio broadcasting in the United States in 1920, along with the concurrent development of sound and color film in that decade, ended the print monopoly of mass media and opened the doors to the immediate (and pervasive) electronic media. By 1928, the United States had three national radio networks: two owned by NBC (the National Broadcasting Company), and one by CBS (the Columbia Broadcasting System). Until 1943, there were four major national radio networks: two owned by NBC, one owned by CBS and one owned by Mutual Broadcasting System. Stations were connected by broadcast-quality, leased telephone lines. NBC's second network became ABC, the American Broadcasting Company.

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