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Broadcast television

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Broadcast television

"Air TV" redirects here. For the anime, see Air (visual novel).

Terrestrial television is a type of television broadcasting which does not involve either satellite transmission or cables.

Instead, transmission is done with radio waves, and antennas or television antenna aerials are used for reception.

The term is more common in Europe, while in North America it is referred to as broadcast television or sometimes over-the-air television (OTA) and requires a tuner to view content.

Terrestrial television broadcasting dates back to the very beginnings of the broadcast television system as a medium itself with the first long-distance public television broadcast from Washington, D.C., on April 7, 1927. The BBC began broadcasting television to the public in 1929, and had a regular schedule of television programmes in 1930. Aside from transmission by high-flying planes moving in a loop using a system developed by Westinghouse called Stratovision, there was virtually no other method of television delivery until the 1950s with the beginnings of cable television, or community antenna television (CATV). The first non-terrestrial method of delivering television signals that in no way depended on a signal originating from a traditional terrestrial source began with the use of communications satellites during the 1960s and 1970s.

Europe

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 is still used in other countries around Europe for PAL broadcasts, though many have plans to phase it out.

The success of terrestrial analogue television across Europe varies from country to country. Although each country has rights to a certain number of frequencies by virtue of the ST61 plan, not all of them have been brought into service.

North America

In North America terrestrial television underwent a revolutionary transformation with the eventual acceptance of the NTSC standard for color television broadcasts in 1953. Later, Europe and the rest of the world either chose between the later PAL and SECAM color television standards, or adopted NTSC. Japan also uses a version of NTSC.

In addition to the threat from cable television, analog terrestrial television is now also subject to competition from satellite television and distribution of video and film content over the Internet. The technology of digital terrestrial television has been developed as a response to these challenges. The rise of digital terrestrial television, especially high-definition television (HDTV), may mark an end to the decline of broadcast television reception via traditional receiving antennas, which can receive over-the-air HDTV signals.

In North America, terrestrial broadcast television operates on TV channels 2 through 6 (VHF-low band, known as band I in Europe), 7 through 13 (VHF-high band, known as band III elsewhere), and 14 through 69 (UHF television band, elsewhere bands IV and V). Channel numbers represent actual frequencies used to broadcast the television signal. Additionally, television translators and boosters can be used to rebroadcast a terrestrial TV signal using an otherwise unused channel to cover areas with marginal reception. A chart showing the North American television bandplan can be found at the North American broadcast television frequencies page.

As of January 8, 2011, analog TV channels 2 through 6, 7 through 13 and 14 through 51 are only used for LPTV translator stations in the U.S. Channels 52 through 69 are still used in exceptional circumstances for LPTV translators in some remote regions of Canada. The Canadian Broadcasting Corporation has received permission to continue analog broadcasting at severely reduced power levels in some mandatory markets until January 8, 2012. It is expected that these transmitters will be shut down rather than converted to digital. Some older cathode ray tube TVs have a built in transmitter.

Asia

Terrestrial television in India started with the experimental telecast starting in Delhi on 15 September 1959 with a small transmitter and a makeshift studio. The regular daily transmission started in 1965 as a part of All India Radio. The television service was extended to Bombay (now Mumbai) and Amritsar in 1972. Up until 1975, only seven Indian cities had a television service and Doordarshan remained the sole provider of television in India. Television services were separated from radio in 1976. National telecasts were introduced in 1982. In the same year, colour TV was introduced in the Indian market. At that time there was only one national channel Doordarshan, which was government owned. The Ramayana and Mahabharata (both being Hindu mythological stories based on religious scriptures of the same names) were the first major television series produced. This serial notched up the world record in viewership numbers for a single program. By the late 1980s more and more people started to own television sets. Though there was a single channel, television programming had reached saturation. Hence the government opened up another channel which had part national programming and part regional. This channel was known as DD 2 later DD Metro'. Both channels were broadcast terrestrially. Now more than 90 percent of the Indian population can receive Doordarshan DD National' programmes through a network of nearly 1,400 terrestrial transmitters.

Digital television

By the mid 1990s, the interest in digital television across Europe was such the CEPT convened the "Chester '97" conference to agree means by which digital television could be inserted into the ST61 frequency plan.

The introduction of digital television in the late 1990s and early years of the 21st century led the ITU to call a Regional Radiocommunication Conference to abrogate the ST61 plan and to put a new plan for digital broadcasting only in its place.

In December 2005 the European Union decided to cease all analog audio and analog video television transmissions by 2012 and switch all terrestrial television broadcasting to digital audio and digital video (all EU countries have agreed on using DVB-T). The Netherlands completed the transition in December 2006, and some EU member states decided to complete their switchover as early as 2008 (Sweden), and (Denmark) in 2009. While the UK began the switch in late 2007, it was not completed until 24 October 2012. Norway ceased all analogue television transmissions on December 1, 2009.[1] Two member states (not specified in the announcement) have expressed concerns that they might not be able to proceed to the switchover by 2012 due to technical limitations; the rest of the EU member states had stopped analog television transmissions by the end 2012.

Many countries are developing and evaluating digital terrestrial television systems.

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 commenced 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 DTV 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.

In North America a specification laid out by the ATSC has become the standard for digital terrestrial television. In the United States the Federal Communications Commission (FCC) set the final deadline for the switchoff of analog service for June 12, 2009. All television receivers must now include a digital tuner. In Canada, the Canadian Radio-television and Telecommunications Commission (CRTC), has set August 31, 2011 as the date that over-the-air analog transmission service will cease in most parts of the country except in Northern Canada.[2] [3]

Competition for radio spectrum

In late 2009, US competition for the limited available radio spectrum led to debate over the possible re-allocation of frequencies currently occupied by television, and the FCC began asking for comments on how to increase the bandwidth available for wireless broadband. Some have proposed mixing the two together, on different channels that are already open (like White Spaces), while others have proposed "repacking" some stations and forcing them off certain channels, just a few years after the same thing was done (without compensation to the broadcasters) in the DTV transition in the United States.

Some US commenters have proposed the closing down of over-the-air 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.

The National Association of Broadcasters has organized to fight such proposals, and public comments are also being taken by the FCC through mid-December 2009, in preparation for a plan to be released in mid-February 2010.

See also

References

External links

  • TVRadioWorld TV stations directory
  • W9WI.com (Terrestrial repeater and TV hobbyist information)
  • TV Coverage maps and Signal Analysis
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