transmission and reception of information by means of electromagnetic waves about 10 to 80 m (33 to 262 feet) in length having frequencies of approximately 29.7 to 3.5 megahertz. During the early 1920s attempts were made to transmit radio signals over long distances by bouncing them off the layers of charged particles in the Earth's ionosphere. The success of these experiments prompted the establishment of worldwide shortwave communication by the late 1930s.

Shortwave broadcasts provide the major source of news and popular entertainment in much of the world except in highly developed regions such as western Europe, North America, and Japan, where government or commercial programming is transmitted within other bands of frequencies. Among the world's most powerful shortwave broadcasting stations are China Radio International (formerly Radio Peking 【Beijing】), the Voice of Russia (formerly Radio Moscow), the British Broadcasting Corporation, and the Voice of America. Besides their use in international broadcasting, shortwave radio frequencies and techniques are utilized to relay telephone and telegraph communications over great distances. Amateur radio stations and portable two-way radios also operate at shortwave frequencies.