Broadcasting is thedistribution ofaudio or electronicmass communications medium, but typically one using theelectromagnetic spectrum (radio waves), in aone-to-many model.^[1] Broadcasting began withAM radio, which came into popular use around 1920 with the spread ofvacuum tuberadio transmitters andreceivers. Before this, most implementations of electronic communication (earlyradio,telephone, andtelegraph) wereone-to-one, with the message intended for a single recipient. The termbroadcasting evolved from its use as the agricultural method of sowing seeds in a field by casting them broadly about.^[2] It was later adopted for describing the widespread distribution of information by printed materials^[3] or by telegraph.^[4] Examples applying it to "one-to-many" radio transmissions of an individual station to multiple listeners appeared as early as 1898.^[5]

Over-the-air broadcasting is usually associated withradio andtelevision, though more recently, both radio and television transmissions have begun to be distributed by cable (cable television). The receiving parties may include the general public or a relatively small subset; the point is that anyone with the appropriate receiving technology and equipment (e.g., a radio or television set) can receive the signal. The field of broadcasting includes both government-managed services such aspublic radio,community radio andpublic television, and privatecommercial radio andcommercial television. The U.S. Code of Federal Regulations, title 47, part 97 definesbroadcasting as "transmissions intended for reception by the general public, either direct or relayed".^[6] Private or two-waytelecommunications transmissions do not qualify under this definition. For example,amateur ("ham") andcitizens band (CB) radio operators are not allowed to broadcast. As defined,transmitting andbroadcasting are not the same.

Transmission of radio and television programs from a radio or television station to home receivers byradio waves is referred to asover the air (OTA) orterrestrial broadcasting and in most countries requires abroadcasting license. Transmissions using a wire or cable, likecable television (which also retransmits OTA stations with theirconsent), are also considered broadcasts but do not necessarily require a license (though in some countries, a license is required). In the 2000s, transmissions of television and radio programs viastreaming digital technology have increasingly been referred to as broadcasting as well.^[7]

In 1894, Italian inventorGuglielmo Marconi began developing a wireless communication using the then-newly discovered phenomenon ofradio waves, showing by 1901 that they could be transmitted across the Atlantic Ocean.^[8] This was the start ofwireless telegraphy by radio. Audio radio broadcasting began experimentally in the first decade of the 20th century. On 17 December 1902, a transmission from the Marconi station inGlace Bay, Nova Scotia, Canada, became the world's first radio message to cross the Atlantic from North America. In 1904, a commercial service was established to transmit nightly news summaries to subscribing ships, which incorporated them into their onboard newspapers.^[9]

World War I accelerated the development of radio formilitary communications. After the war, commercial radioAM broadcasting began in the 1920s and became an important mass medium for entertainment and news.World War II again accelerated the development of radio for the wartime purposes of aircraft and land communication, radio navigation, and radar.^[10] Development of stereoFM broadcasting of radio began in the 1930s in the United States and the 1970s in the United Kingdom, displacing AM as the dominant commercial standard.^[11]

On 25 March 1925,John Logie Baird demonstrated the transmission of moving pictures at the London department storeSelfridges. Baird's device relied upon theNipkow disk and thus became known as themechanical television. It formed the basis of experimental broadcasts done by theBritish Broadcasting Corporation beginning on 30 September 1929.^[12] However, for most of the 20th century, televisions depended on thecathode-ray tube invented byKarl Braun. The first version of such a television to show promise was produced byPhilo Farnsworth and demonstrated to his family on 7 September 1927.^[13] AfterWorld War II, interrupted experiments resumed and television became an important home entertainment broadcast medium, usingVHF andUHF 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 ofanalog signals usinganalog transmission techniques but in the 2000s, broadcastersswitched todigital signals usingdigital transmission. An analog signal is anycontinuous signal representing some other quantity, i.e.,analogous to another quantity. For example, in an analogaudio signal, the instantaneous signalvoltage varies continuously with thepressure of the sound waves.^{[citation needed]} In contrast, adigital signal represents the original time-varying quantity as asampled sequence ofquantized values which imposes somebandwidth anddynamic range constraints on the representation. In general usage, broadcasting most frequently refers to the transmission of information and entertainment programming from various sources to the general public:^{[citation needed]}

• Analog audio radio (AM, FM) vs.digital audio radio (HD radio),digital audio broadcasting (DAB),satellite radio anddigital Radio Mondiale (DRM)
• Analog television vs.digital television
• Wireless

The world's technological capacity to receive information through one-way broadcast networks more than quadrupled during the two decades from 1986 to 2007, from 432exabytes of (optimally compressed) information, to 1.9zettabytes.^[14] This is the information equivalent of 55 newspapers per person per day in 1986, and 175 newspapers per person per day by 2007.^[15]

In a broadcast system, the central high-poweredbroadcast tower transmits a high-frequencyelectromagnetic wave to numerous receivers. The high-frequency wave sent by the tower is modulated with a signal containing visual or audio information. The receiver is thentuned so as to pick up the high-frequency wave and ademodulator is used to retrieve the signal containing the visual or audio information. The broadcast signal can be either analog (signal is varied continuously with respect to the information) or digital (information is encoded as a set of discrete values).^[16][17]

Historically, there have been several methods used for broadcastingelectronic media audio and video to the general public:

• Telephone broadcasting (1881–1932): the earliest form of electronic broadcasting (not counting data services offered by stocktelegraph companies from 1867, ifticker-tapes are excluded from the definition). Telephone broadcasting began with the advent ofThéâtrophone ("Theatre Phone") systems, which were telephone-based distribution systems allowing subscribers to listen to liveopera andtheatre performances over telephone lines, created by French inventorClément Ader in 1881. Telephone broadcasting also grew to includetelephone newspaper services for news and entertainmentprogramming which were introduced in the 1890s, primarily located in largeEuropean cities. These telephone-basedsubscription services were the first examples of electrical/electronic broadcasting and offered a wide variety of programming.^{[citation needed]}
• Radio broadcasting (experimentally from 1906, commercially from 1920);audio signals sent through the air asradio waves from atransmitter, picked up by anantenna and sent to areceiver.Radio stations can be linked inradio networks to broadcast commonradio programs, either inbroadcast syndication,simulcast orsubchannels.
  • Television broadcasting (telecast), experimentally from 1925,commercially from the 1930s: an extension of radio to includevideo signals.
• Cable radio (also calledcable FM, from 1928) andcable television (from 1932): both viacoaxial cable, originally serving principally as transmission media for programming produced at either radio ortelevision stations, but later expanding into a broad universe of cable-originatedchannels.
• Direct-broadcast satellite (DBS) (fromc. 1974) andsatellite radio (fromc. 1990): meant for direct-to-home broadcast programming (as opposed to studio network uplinks and down-links), provides a mix of traditional radio or television broadcast programming, or both, with dedicated satellite radio programming. (See also:Satellite television)
• Webcasting of video/television (fromc. 1993) and audio/radio (fromc. 1994) streams: offers a mix of traditional radio and television station broadcast programming with dedicatedInternet radio andInternet television.

There are several means of providing financial support for continuous broadcasting:

• Commercial broadcasting: for-profit, usually privately owned stations, channels, networks, or services providing programming to the public, supported by the sale of air time to advertisers forradio ortelevision advertisements during or in breaks between programs, often in combination with cable orpay cable subscription fees.
• Public broadcasting: usuallynon-profit, publicly owned stations or networks supported by license fees, government funds, grants from foundations, corporateunderwriting, audience memberships, contributions or a combination of these.
• Community broadcasting: a form ofmass media in which atelevision station, or aradio station, is owned, operated orprogrammed, by a community group to provide programs of local interest known aslocal programming. Community stations are most commonly operated bynon-profit groups orcooperatives; however, in some cases they may be operated by a localcollege oruniversity, acable company or a municipal government.
• Internet Webcast: the audience pays to recharge and buy virtual gifts for the anchor, and the platform converts the gifts into virtual currency. The anchor withdraws the virtual currency, which is drawn by the platform. If the anchor belongs to a trade union, it will be settled by the trade union and the live broadcasting platform, and the anchor will get the salary and part of the bonus. This is the most common profit model of live broadcast products.

Broadcasters may rely on a combination of thesebusiness models. For example, in the United States,National Public Radio (NPR) and thePublic Broadcasting Service (PBS, television) supplement public membership subscriptions and grants with funding from theCorporation for Public Broadcasting (CPB), which is allocated bi-annually by Congress. US public broadcasting corporate and charitable grants are generally given in consideration ofunderwriting spots which differ from commercial advertisements in that they are governed by specificFCC restrictions, which prohibit the advocacy of a product or a "call to action".

The first regular television broadcasts started in 1937. Broadcasts can be classified asrecorded orlive. The former allows correcting errors, and removing superfluous or undesired material, rearranging it, applyingslow-motion and repetitions, and other techniques to enhance the program. However, some live events likesports television can include some of the aspects including slow-motion clips of important goals/hits, etc., in between thelive television telecast. American radio-network broadcasters habitually forbade prerecorded broadcasts in the 1930s and 1940s, requiring radio programs played for the Eastern and Centraltime zones to be repeated three hours later for the Pacific time zone (See:Effects of time on North American broadcasting). This restriction was dropped for special occasions, as in the case of the Germandirigible airshipHindenburg disaster atLakehurst, New Jersey, in 1937. DuringWorld War II, prerecorded broadcasts from war correspondents were allowed on U.S. radio. In addition, American radio programs were recorded for playback byArmed Forces Radioradio stations around the world.

A disadvantage of recording first is that the public may learn the outcome of an event before the recording is broadcast, which may be aspoiler. Prerecording may be used to preventannouncers from deviating from an officially approvedscript during alive radio broadcast, as occurred withpropaganda broadcasts from Germany in the 1940s and withRadio Moscow in the 1980s. Many events are advertised as being live, although they are often recorded live (sometimes called "live-to-tape"). This is particularly true of performances of musical artists on radio when they visit for an in-studioconcert performance. Similar situations have occurred intelevision production ("The Cosby Show is recorded in front of alive television studioaudience") andnews broadcasting.

A broadcast may be distributed through several physical means. If coming directly from theradio studio at a single station ortelevision station, it is sent through thestudio/transmitter link to thetransmitter and hence from thetelevision antenna located on theradio masts and towers out to the world. Programming may also come through acommunications satellite, played either live or recorded for later transmission. Networks of stations maysimulcast the same programming at the same time, originally viamicrowave link, now usually by satellite. Distribution to stations or networks may also be through physical media, such asmagnetic tape,compact disc (CD),DVD, and sometimes other formats. Usually these are included in another broadcast, such as whenelectronic news gathering (ENG) returns a story to the station for inclusion on anews programme.

The final leg of broadcast distribution is how the signal gets to the listener or viewer. It may come over the air as with aradio station ortelevision station to anantenna andradio receiver, or may come throughcable television^[18] orcable radio (orwireless cable) via the station or directly from a network. TheInternet may also bring eitherinternet radio orstreaming media television to the recipient, especially withmulticasting allowing the signal andbandwidth to be shared. The termbroadcast network is often used to distinguish networks that broadcast over-the-air television signals that can be received using atuner inside atelevision set with atelevision antenna from so-called networks that are broadcast only viacable television (cablecast) orsatellite television that uses adish antenna. The termbroadcast television can refer to thetelevision programs of such networks.

The sequencing of content in a broadcast is called aschedule. As with all technological endeavors, a number of technical terms andslang have developed. A list of these terms can be found atList of broadcasting terms.^[19]Television andradio programs are distributed through radio broadcasting orcable, often both simultaneously. By coding signals and having acable converter box withdecoding equipment inhomes, the latter also enablessubscription-based channels,pay-tv andpay-per-view services. In his essay,John Durham Peters wrote thatcommunication is a tool used for dissemination. Peters stated, "Dissemination is a lens—sometimes a usefully distorting one—that helps us tackle basic issues such as interaction, presence, and space and time ... on the agenda of any futurecommunication theory in general".^[20]: 211 Dissemination focuses on the message being relayed from one main source to one largeaudience without the exchange ofdialogue in between. It is possible for the message to bechanged or corrupted by government officials once the main source releases it. There is no way to predetermine how the larger population or audience will absorb the message. They can choose to listen, analyze, or ignore it. Dissemination in communication is widely used in the world of broadcasting.

Broadcasting focuses on getting a message out and it is up to the general public to do what they wish with it. Peters also states that broadcasting is used to address an open-ended destination.^[20]: 212 There are many forms of broadcasting, but they all aim to distribute a signal that will reach the targetaudience. Broadcasters typically arrange audiences into entire assemblies.^[20]: 213 In terms of media broadcasting, aradio show can gather a large number of followers who tune in every day to specifically listen to that specificdisc jockey. The disc jockey follows the script for their radio show and just talks into themicrophone.^[20] They do not expect immediate feedback from any listeners. The message is broadcast across airwaves throughout the community, but the listeners cannot always respond immediately, especially since many radio shows are recorded prior to the actual air time. Conversely, receivers can select opt-in or opt-out of getting broadcast messages using an Excel file, offering them control over the information they receive.

Broadcast engineering is the field ofelectrical engineering, and now to some extentcomputer engineering andinformation technology, which deals withradio andtelevision broadcasting.Audio engineering andRF engineering are also essential parts of broadcast engineering, being their ownsubsets of electrical engineering.^[21]

Broadcast engineering involves both thestudio andtransmitter aspects (the entireairchain), as well asremote broadcasts. Everystation has a broadcastengineer, though one may now serve an entire station group in a city. In smallmedia markets the engineer may work on acontract basis for one or more stations as needed.^[21][22][23]

• International bibliography – History of wireless and radio broadcasting

• Barnouw Erik.The Golden Web (Oxford University Press, 1968);The Sponsor (1978);A Tower in Babel (1966).
• Covert Cathy, and Stevens John L.Mass Media Between the Wars (Syracuse University Press, 1984).ISBN 978-0-8156-2307-6
• Tim Crook;International Radio Journalism: History, Theory and Practice Routledge, 1998
• John Dunning;On the Air: The Encyclopedia of Old-Time Radio Oxford University Press, 1998
• Ewbank Henry and Lawton Sherman P.Broadcasting: Radio and Television (Harper & Brothers, 1952).
• Maclaurin W. Rupert.Invention and Innovation in the Radio Industry (The Macmillan Company, 1949).
• Robert W. McChesney;Telecommunications, Mass Media, and Democracy: The Battle for the Control of U.S. Broadcasting, 1928–1935 Oxford University Press, 1994
• Gwenyth L. Jackaway;Media at War: Radio's Challenge to the Newspapers, 1924–1939 Praeger Publishers, 1995
• Lazarsfeld Paul F.The People Look at Radio (University of North Carolina Press, 1946).
• Schramm Wilbur, ed.Mass Communications (University of Illinois Press, 1960).
• Schwoch James.The American Radio Industry and Its Latin American Activities, 1900–1939 (University of Illinois Press, 1990).ISBN 978-0-252-01690-5
• Slater Robert.This ... is CBS: A Chronicle of 60 Years (Prentice Hall, 1988).ISBN 978-0-13-919234-0
• Sterling Christopher H.Electronic Media, A Guide to Trends in Broadcasting and Newer Technologies 1920–1983 (Praeger, 1984).ISBN 978-0-275-91277-2
• Sterling Christopher, and Kittross John M.Stay Tuned: A Concise History of American Broadcasting (Wadsworth, 1978).
• Wells, Alan,World Broadcasting: A Comparative View,Greenwood Publishing Group, 1996.ISBN 1-56750-245-8

• Radio Locator, for American radio station with format, power, and coverage information.
• Jim Hawkins' Radio and Broadcast Technology Page – History of broadcast transmitter
• Indie Digital Cinema Services – Broadcast Industry Glossary