U.S. Code of Federal Regulations, title 47, part 97 defines « broadcasting » as « transmissions intended for reception by the general public, either direct or relayed ». Private or two-way telecommunications transmissions do not qualify under this definition. For example, amateur (« ham ») and citizens band (CB) radio operators are not allowed to broadcast. As defined, « transmitting » and « broadcasting » are not the same. Transmission of radio and television programs from a radio or television station to home receivers over the spectrum is referred to as OTA (over the air) or terrestrial broadcasting and in most countries requires a broadcasting license.
Transmissions using a combination of satellite and wired transmission, like cable television (which also retransmits OTA stations with their consent), are also considered broadcasts, and do not require a license. Transmissions of television and radio via streaming digital technology have increasingly been referred to as broadcasting as well, though strictly speaking this is incorrect.
Broadcasting is the distribution of audio and/or video content to a dispersed audience via any electronic mass communications medium, but typically one using the electromagnetic spectrum (radio waves), in a one-to-many model. Broadcasting began with AM radio broadcasting which came into popular use starting with the invention of the crystal detector in 1906. Before this, all forms of electronic communication, radio, telephone, and telegraph, were « one-to-one », with the message intended for a single recipient. The term « broadcasting », borrowed from the agricultural method of sowing seeds in a field by casting them broadly about, was coined by either KDKA manager Frank Conrad or RCA historian George Clark around 1920 to distinguish this new activity of « one-to-many » communication; a single radio station transmitting to multiple listeners.
Over the air broadcasting is usually associated with radio and television, though in practice radio and television transmissions take place using both wires and radio waves. The receiving parties may include the general public or a relatively small subset; the point is that anyone with the appropriate receiving technology can receive the signal. The field of broadcasting includes a wide range of practices, from relatively private exchanges such as public radio, community radio and commercial radio, public television, and commercial television.
The earliest broadcasting consisted of sending telegraph signals over the airwaves, using Morse code. This was particularly important for ship-to-ship and ship-to-shore communication, but it became increasingly important for business and general news reporting, and as an arena for personal communication by radio amateurs (Douglas, op. cit.). Audio broadcasting began experimentally in the first decade of the 20th century. By the early 1920s radio broadcasting became a household medium, at first on the AM band and later on FM. Television broadcasting started experimentally in the 1920s and became widespread after World War II, using VHF and UHF spectrum. Satellite broadcasting was initiated in the 1960s and moved into general industry usage in the 1970s, with DBS (Direct Broadcast Satellites) emerging in the 1980s.
Originally all broadcasting was composed of analog signals using analog transmission techniques but more recently broadcasters have switched to digital signals using digital transmission. In general usage, broadcasting most frequently refers to the transmission of information and entertainment programming from various sources to the general public.