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Terrestrial television


Terrestrial television is a type of television broadcasting in which the television signal is transmitted by radio waves from the terrestrial (Earth-based) transmitter of a television station to a TV receiver having an antenna. The term terrestrial is more common in Europe and Latin America, while in the United States it is called broadcast or over-the-air television (OTA). The term "terrestrial" is used to distinguish this type from the newer technologies of satellite television (direct broadcast satellite or DBS television), in which the television signal is transmitted to the receiver from an overhead satellite, cable television, in which the signal is carried to the receiver through a cable, and Internet Protocol television, in which the signal is received over an Internet stream or on a network utilizing the Internet Protocol. Terrestrial television stations broadcast on television channels with frequencies between about 52 and 600 MHz in the VHF and UHF bands. Since radio waves in these bands travel by line of sight, reception is limited by the visual horizon to distances of 4060 miles (6497 km).

There was no other method of television delivery until the 1950s with the beginnings of cable television and community antenna television (CATV). CATV was, initially, only a re-broadcast of over-the-air signals. With the widespread adoption of cable across the United States in the 1970s and 1980s, viewing of terrestrial television broadcasts has been in decline; in 2018, it was estimated that about 14% of US households used an antenna. A slight increase in use began after the 2009 final conversion to digital terrestrial television broadcasts, which offer HDTV image quality as an alternative to CATV for cord cutters.

Following the ST61 conference, UHF frequencies were first used in the UK in 1964 with the introduction of BBC2. In UK, VHF channels were kept on the old 405-line system, while UHF was used solely for 625-line broadcasts (which later used PAL colour). Television broadcasting in the 405-line system continued after the introduction of four analogue programmes in the UHF bands until the last 405-line transmitters were switched off on January 6, 1985. VHF Band III was used in other countries around Europe for PAL broadcasts until planned phase out and switchover to digital television.

In the late 1990s and early 2000s, the Advanced Television Systems Committee developed the ATSC standard for digital high definition terrestrial transmission. This standard was eventually adopted by many American countries, including the United States, Canada, Dominican Republic, Mexico, El Salvador, Guatemala and Honduras; however, the three latter countries ditched it in favour of ISDB-Tb.

Terrestrial television broadcast in Asia started as early as 1939 in Japan through a series of experiments done by NHK Broadcasting Institute of Technology. However, these experiments were interrupted by the beginning of the World War II in the Pacific. On February 1, 1953, NHK (Japan Broadcasting Corporation) began broadcasting. On August 28, 1953, Nippon TV (Nippon Television Network Corporation), the first commercial television broadcaster in Asia was launched. Meanwhile, in the Philippines, Alto Broadcasting System (now ABS-CBN), the first commercial television broadcaster in Southeast Asia, launched its first commercial terrestrial television station DZAQ-TV on October 23, 1953, with the help of Radio Corporation of America (RCA).

Australia has adopted the DVB-T standard and the government's industry regulator, the Australian Communications and Media Authority, has mandated that all analogue transmissions will cease by 2012. Mandated digital conversion started early in 2009 with a graduated program. The first centre to experience analog switch-off will be the remote Victorian regional town of Mildura, in 2010. The government will supply underprivileged houses across the nation with free digital set-top converter boxes in order to minimise any conversion disruption. Australia's major free-to-air television networks have all been granted digital transmission licences and are each required to broadcast at least one high-definition and one standard-definition channel into all of their markets.

Some US commentators have proposed the closing down of terrestrial TV broadcasting, on the grounds that available spectrum might be better used, and requiring viewers to shift to satellite or cable reception. This would eliminate mobile TV, which has been delayed several years by the FCC's decision to choose ATSC and its proprietary 8VSB modulation, instead of the worldwide COFDM standard used for all other digital terrestrial broadcasting around the world. Compared to Europe and Asia, this has hamstrung mobile TV in the US, because ATSC cannot be received while in motion (or often even while stationary) without ATSC-M/H as terrestrial DVB-T or ISDB-T can even without DVB-H or 1seg.