Terrestrial television
From Wikipedia, the free encyclopedia
Terrestrial television (also known as over-the-air, OTA or broadcast television) was the traditional method of television broadcast signal delivery prior to the advent of cable and satellite television. Although still in wide use, in some countries and many densly-populated areas it is decreasing in use but in others, digital terrestrial has become popular. It works via radio waves transmitted through open space, usually unencrypted (commonly known as "free-to-air" television).
Terrestrial television broadcasting dates back to the very beginnings of television as a medium itself with the first long-distance public television broadcast from Washington, D.C., on April 7, 1927. 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 advent 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.
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[edit] North America
In the United States and most of the rest of North America as well, 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 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 here.
[edit] Europe
In Europe, a planning conference ("ST61") held under the auspices of the International Telecommunications Union in Stockholm in 1961 allocated frequencies the Bands IV and V for the first time for broadcast television use. It also superseded the 1951 Plan (also made in Stockholm) which had first allocated Band II frequencies for FM radio and Band III frequencies for television.
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 bought into service.
[edit] 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 Radiocommunications Conference to abrogate the ST61 plan and to put a new plan for digital broadcasting only in its place.
In December 2005 the EU has decided to cease all analogue television transmissions by the year 2012 and switch all terrestrial television broadcasting to digital (all EU countries have agreed on using DVB-T). Some EU member states have decided to complete this switchover as early as October 2006 (the Netherlands) 2008 (Sweden) and 2009 (Denmark). 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 are expected to stop analogue television transmissions by 2012.
Many countries are developing and evaluating digital terrestrial television systems.
In North America a specification laid out by the ATSC has become the standard for digital terrestrial television. In the United States the FCC has set a final deadline for the switchoff of analog service for January 2009. All television receivers with a 25 inch display or larger must now include a digital tuner. Sets from 13 to 24 inches must include digital tuners by July 1, 2007.
[edit] See also
- Broadcast television systems
- Lists of television channels for lists by country and language.
- Television channel frequencies
- DVB-T
- ATSC tuner
[edit] References
[edit] External links
- TVRadioWorld TV stations directory
- W9WI.com (Terrestrial repeater and TV hobbyist information)
