Terrestrial television | Wikipedia audio article

Terrestrial television | Wikipedia audio article


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 40–60 miles
(64–97 km). Terrestrial television was the first technology
used for television broadcasting. The BBC began broadcasting in 1929 and by
1930 many radio stations had a regular schedule of experimental television programmes. However, these early experimental systems
had insufficient picture quality to attract the public, due to their mechanical scan technology,
and television did not become widespread until after World War II with the advent of electronic
scan television technology. The television broadcasting business followed
the model of radio networks, with local television stations in cities and towns affiliated with
television networks, either commercial (in the US) or government-controlled (in Europe),
which provided content. Television broadcasts were in black and white
until the transition to color television in the 1950s and 60s.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 2013, it was estimated that about 7% 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.==Analogue terrestrial television=====
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 was used in other countries around
Europe for PAL broadcasts until planned phase out and switchover to digital television. The success of analogue terrestrial television
across Europe varied from country to country. Although each country had rights to a certain
number of frequencies by virtue of the ST61 plan, not all of them were brought into service.===Americas===
In 1941, the first NTSC standard was introduced by the National Television System Committee. This standard defined a transmission scheme
for a black and white picture with 525 lines of vertical resolution at 60 fields per second. In the early 1950s, this standard was superseded
by a backwards-compatible standard for color television. The NTSC standard was exclusively being used
in the Americas as well as Japan until the introduction of digital terrestrial television
(DTT). While Mexico have ended all its analogue television
broadcasts and the US and Canada have shut down nearly all of their analogue TV stations,
the NTSC standard continues to be used in the rest of Latin American countries while
testing their DTT platform.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.The
Pan-American terrestrial television operates on analog channels 2 through 6 (VHF-low band,
54 to 88 MHz, known as band I in Europe), 7 through 13 (VHF-high band, 174 to 216 MHz,
known as band III elsewhere), and 14 through 51 (UHF television band, 470 to 698 MHz, elsewhere
bands IV and V). Unlike with analog transmission, ATSC channel
numbers do not correspond to radio frequencies. Instead, a virtual channel is defined as part
of the ATSC stream metadata so that a station can transmit on any frequency but still show
the same channel number. Additionally, free-to-air television repeaters
and signal boosters can be used to rebroadcast a terrestrial television signal using an otherwise
unused channel to cover areas with marginal reception. (see Pan-American television frequencies for
frequency allocation charts)Analog television 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 by some existing stations, but these channels must be vacated if telecommunications
companies notify the stations to vacate that signal spectrum. By convention, broadcast television signals
are transmitted with horizontal polarization.===Asia===
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).==Digital terrestrial 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 terrestrial 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 DTT broadcasting only in
its place. In December 2005, the European Union decided
to cease all analogue audio and analogue 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 to switch off analogue
broadcasts, region by region, in late 2007, it was not completed until 24 October 2012. Norway ceased all analogue television transmissions
on 1 December 2009. 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 analogue
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 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. 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 switch-off of analogue service for 12
June 2009. All television receivers must now include
a DTT tuner using ATSC. In Canada, the Canadian Radio-television and
Telecommunications Commission (CRTC) set 31 August 2011 as the date that terrestrial analogue
transmission service ceased in metropolitan areas and provincial capitals. In Mexico, the Federal Telecommunications
Institute (IFT) set the final deadline for the end of analogue terrestrial television
for 31 December 2015.==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 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. The National Association of Broadcasters has
organised 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

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