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In the United States, for most of the history of broadcasting, there were only three or four major commercial national broadcast networks. From 1946 to 1956, these were ABC, CBS, NBC and DuMont (though the Paramount Television Network had some limited success during these years). From 1956 to 1986, the "Big Three" national commercial networks were ABC, CBS, and NBC (with a few limited attempts to challenge them, such as National Telefilm Associates (its NTA Film Network ) and the Overmyer Network). From 1954 to 1970, National Educational Television was the national clearinghouse for public television programming; the Public Broadcasting Service (PBS) succeeded it in 1970. Today, more than 50 national broadcasting networks exist. Other than the non-commercial educational (NCE) PBS, which is composed of member stations, the largest broadcast television networks are the traditional Big Three television networks (ABC, CBS and NBC). Many other large networks exist, however, notably Fox and The CW which air original programming for two hours each night instead of three like the original "Big Three" do, as well as syndication services like MyNetworkTV and Ion Television which feature reruns of recent popular shows with little to no original programming. Fox has just about the same household reach percentage as the Big Three, and is therefore often considered a peer to ABC, NBC, and CBS since it has also achieved equal or better ratings since the late 1990s. Most media outlets now include Fox in what they refer to as the "Big Four" television networks. The transition to digital broadcasting in 2009 has allowed for television stations to offer additional programming options through digital subchannels, one or more supplementary programming streams to the station's primary channel that are achieved through multiplexing of a station's signal. A number of new commercial networks airing specialty programming such as movies, reruns of classic series and lifestyle programs have been created from companies like Weigel Broadcasting, Luken Communications and even owners of the major networks such as The Walt Disney Company (through the Disney–ABC Television Group subsidiary) and Comcast (through the NBCUniversal subsidiary). Through the use of multicasting, there have also been a number of new Spanish-language and non-commercial public television networks that have launched. Broadcast networks in the United States can be divided into four categories: * Commercial broadcast networks – which air English-language programming to a general audience (for example, CBS); * Spanish-language broadcasting networks – fully programmed networks which air Spanish-language programming to a primarily Hispanic and Latino audience (for example, Telemundo and Univision); * Educational and other non-commercial broadcast networks – which air English- and some foreign-language television programming, intended to be educational in nature or otherwise of a sort not found on commercial television (for example, PBS); * Religious broadcast networks – which air religious study and other faith-based programs, and in some cases, family-oriented secular programs (for example, Daystar). Each network sends its signal to many local affiliate television stations across the country. These local stations then air the "network feed," with programs broadcast by each network being viewed by up to tens of millions of households across the country. In the case of the largest networks, the signal is sent to over 200 stations. In the case of the smallest networks, the signal may be sent to just a dozen or fewer stations. As of the 2015-16 television season, there are an estimated 116.4 million households in the United States with at least one television set.〔http://www.nielsen.com/us/en/insights/news/2015/nielsen-estimates-116-4-million-tv-homes-in-the-us-for-the-2015-16-tv-season.html〕 ==Table of broadcast networks== All of the networks listed below operate a number of terrestrial television stations. In addition, several of these networks are also aired on cable and satellite services. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「List of United States over-the-air television networks」の詳細全文を読む スポンサード リンク
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