Radio broadcasting

Radio broadcasting is the transmission of electromagnetic radiation (radio waves) to receivers over a wide territory. Most broadcasts are audio (sound), sometimes with embedded metadata. Listeners need a broadcast radio receiver to pick up these signals. "Terrestrial" broadcasts, including AM, FM and DAB stations, originate signals from a land-based transmitter, while "satellite radio" signals originate from a satellite in Earth orbit.

Individual own programming, or are affiliated with a radio network that provides content, either in broadcast syndication or by simulcasting, or both. The most common transmission technologies are analog and digital signals. Analog radio uses one of two modulation methods: amplitude modulation, used by AM radio, or frequency modulation, for FM radio. A newer technique, digital radio stations, transmit using one of several different digital audio standards, such as DAB (Digital Audio Broadcasting), HD radio, or DRM (Digital Radio Mondiale).

Electronic distribution originated, to a limited extent, with the invention of the telegraph. The most common example, "tickers", were primarily used to distribute stock price information. An additional subscription service was time signals. The concept of audio broadcasting was first developed after the invention of telephone. In a few locations, most commonly in Europe, telephone newspapers were established, to provide news and entertainment to subscribers. These systems had the advantage of being able to charge individual customers. However, a lack of a way to amplify signals meant that their ranges were generally limited to a single municipality.

Some early inventors foresaw wireless transmission's potential. In 1902, Nathan Stubblefield, who had developed wireless transmissions using ground conduction, envisioned that: "...any one having a receiving instrument, which would consist merely of a telephone receiver and a few feet of wire, and a signaling gong, could, upon being signaled by a transmitting station in Washington, or nearer, if advisable, be informed of weather news. Eventually it will be used for the general transmission of news of every description."

Although it was quickly recognized that radio transmissions were capable of being broadcast to a scattered audience without needing connecting wires, there was skepticism about its finances. In an 1898 review of early radio transmissions, then known as "Hertzian telegraphy", a reviewer opined: "As to the practical applications, there were occasions when one wanted to 'shout to the world'—as in distributing political speeches to the Press—and for such a purpose the Hertz-wave and the coherer might be of service. But did not Prof. Lodge forget that no one wants to pay for shouting to the world on a system by which it would be impossible to prevent non-subscribers from benefiting gratuitously?". Another limitation was that many countries required listeners to be licensed in order to operate a radio receiver.

The earliest radio broadcasting stations transmitted radiotelegraphy dots-and-dashes, for such things as time signals and weather reports, or provided news summaries intended for inclusion in shipboard newspapers. This had limited audiences, because of the need to understand Morse code. Because there was no way to collect fees from listeners, these stations were commonly operated by national governments. Beginning in 1904, the U.S. Navy broadcast daily time signals and weather reports, and a Canadian Marconi station in Camperdown, Nova Scotia began transmitting time signals in 1907. In Europe, a station located at the Eiffel Tower in Paris, France, transmitted time signals that were audible throughout the continent.

Although most radio stations during the first two decades of the 1900s employed radiotelegraphic transmissions, there was also experimental development of audio transmissions, mostly using "amplitude modulation" (AM) signals. The first AM technologies included high-frequency spark, alternator, and arc transmitters. However, it was not until the development of vacuum-tube (also known as "valve") transmitters that widespread audio broadcasting became practical. In addition, most early experimenters worked to create radiotelephone systems for private communication, and few were interested in broadcasting information and entertainment to general audiences.

Early examples of audio broadcasts included: