Radio

Although parts of the various radio bands—short-wave, long-wave, medium-wave, very-high frequency, and ultrahigh frequency—are allocated for a variety of purposes, the term short-wave radio generally refers to radiobroadcasts in the high-frequency range (3 to 30 MHz) beamed for long distances, especially in international communication. Microwave communication via satellite, however, provides signals with superior reliability and freedom from error.

Amateur, or “ham,” radio is also commonly thought of as short-wave, although amateur operators have been allotted frequencies in the medium-wave band, the very-high-frequency band, and the ultrahigh-frequency band as well as the short-wave band. Certain of these frequencies have restrictions designed to make them available to maximum numbers of users.

During the rapid development of radio after World War I, amateur operators executed such spectacular feats as the first transatlantic radio contact (1921). They have also provided valuable voluntary assistance during emergencies when normal communications are disrupted. Amateur radio organizations have launched a number of satellites piggyback with regular launches by the United States, the former Soviet Union, and the European Space Agency. These satellites are usually called Oscar, for Orbiting Satellites Carrying Amateur Radio. The first, Oscar 1, orbited in 1961, was also the first nongovernmental satellite; the fourth, in 1965, provided the first direct-satellite communications between the U.S. and the Soviet Union. More than 1.5 million people worldwide were licensed amateur radio operators in the early 1980s. See also Citizens Band Radio.

The ability to webcast radio programs over the Internet had a major impact on shortwave broadcasting. In the early 2000s the BBC dropped their shortwave radio service to the United States, Canada, Australia, and other developed countries since their programs were available through computers over the World Wide Web. The widespread use of personal computers with Internet access to chat groups and personal Web pages also replaced some of the hobby aspects of amateur radio in popularity.

Immense developments in radio communication technology after World War II helped make possible space exploration, most dramatically in the Apollo moon-landing missions (1969-72). Sophisticated transmitting and receiving equipment was part of the compact, very-high-frequency, communication system on board the command modules and the lunar modules. The system performed voice and ranging functions simultaneously, calculating the distance between the two vehicles by measuring the time lapse between the transmission of tones and the reception of the returns. The voice signals of the astronauts were also transmitted simultaneously around the world by a communications network.

In the 1990s cellular radio telephones (cell phones) became one of the most important and widespread uses of radio communication. By the early 21st century, billions of people worldwide had access to telephone service with lightweight portable cell phones capable of communicating worldwide through radio relays and satellite links. Cell phones have become particularly important in developing countries where landlines for telephones often do not exist outside of large cities. In remote rural areas an individual who owns a cell phone may charge a small fee to let others use the phone service. Such phone service can have a major economic impact in impoverished regions, permitting access to banking services, providing information on prices of crops, and creating small-business contacts.

Digital and satellite radio also greatly expanded the possibilities of radio. Not only does digital radio provide superior sound quality, but it permits such additional services as multiple audio-programming channels, on-demand audio services, and interactive features, as well as targeted advertising. Wireless Internet allows users of computers and portable media devices to access the World Wide Web from all kinds of locations. Personal digital assistants (PDAs) also use radio to access e-mail and other services, including GPS information from satellites. The transition to digital television is expected to free up a large part of the radio spectrum previously used to broadcast analog television. These frequencies may be available for many more wireless uses in the future.