A
television channel is a physical or virtual
channelIn telecommunications and computer networking, a communication channel, or channel, refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel...
over which a
television stationA television station is a business, organisation or other such as an amateur television operator that transmits content over terrestrial television. A television transmission can be by analog television signals or, more recently, by digital television. Broadcast television systems standards are...
or
television networkA television network is a telecommunications network for distribution of television program content, whereby a central operation provides programming to many television stations or pay TV providers. Until the mid-1980s, television programming in most countries of the world was dominated by a small...
is distributed. For example, in
North AmericaNorth America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, "channel 2" refers to the broadcast or cable band of 54 to 60 MHz, with
carrierIn telecommunications, a carrier wave or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal...
frequencies of 55.25 MHz for
NTSCNTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
analog video (VSB) and 59.75 MHz for analog audio (
FMIn telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
), or 55.31 MHz for digital
ATSCATSC standards are a set of standards developed by the Advanced Television Systems Committee for digital television transmission over terrestrial, cable, and satellite networks....
(
8VSB8VSB is the modulation method used for broadcast in the ATSC digital television standard. ATSC and 8VSB modulation is used primarily in North America; in contrast, the DVB-T standard uses COFDM....
). Channels may be shared by many different television stations or cable-distributed channels depending on the location and service provider.
Depending on the multinational
bandplanA bandplan or band plan is a plan for using a particular band of radio frequencies, that are a portion of the electromagnetic spectrum . Each bandplan defines the frequency range to be included, how channels are to be defined, and what will be carried on those channels...
for a given region,
analog televisionAnalog television is the analog transmission that involves the broadcasting of encoded analog audio and analog video signal: one in which the message conveyed by the broadcast signal is a function of deliberate variations in the amplitude and/or frequency of the signal...
channels are typically 6, 7, or 8 MHz in bandwidth, and therefore
television channel frequenciesThe following tables show the frequencies assigned to broadcast television channels in various regions of the world, along with the ITU letter designator for the system used. The frequencies shown are for the video and audio carriers. The channel itself occupies several megahertz of bandwidth....
vary as well. Channel numbering is also different.
Digital televisionDigital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...
channels are the same for legacy reasons, however through
multiplexingThe multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
, each physical
radio frequencyRadio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
(RF) channel can carry several
digital subchannelIn broadcasting, digital subchannels are a means to transmit more than one independent program at the same time from the same digital radio or digital television station on the same radio frequency channel. This is done by using data compression techniques to reduce the size of each individual...
s. On
satelliteA communications satellite is an artificial satellite stationed in space for the purpose of telecommunications...
s, each
transponderIn telecommunication, the term transponder has the following meanings:...
normally carries one channel, however
small, independent channelsSingle channel per carrier refers to using a single signal at a given frequency and bandwidth. Most often, this is used on broadcast satellites to indicate that radio stations are not multiplexed as subcarriers onto a single video carrier, but instead independently share a transponder...
can be used on each transponder, with some loss of bandwidth due to the need for
guard band-Radio and electronic signalling:In radio, a guard band is an unused part of the radio spectrum between radio bands, for the purpose of preventing interference....
s between unrelated transmissions.
ISDBIntegrated Services Digital Broadcasting is a Japanese standard for digital television and digital radio used by the country's radio and television stations. ISDB replaced the previously used MUSE "Hi-vision" analogue HDTV system...
, used in
JapanJapan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
and
BrazilBrazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
, has a similar segmented mode.
Channel separation on over-the-air channels is accomplished by skipping at least one channel between two analog stations'
frequency allocationUse of radio frequency bands of the electromagnetic spectrum is regulated by governments in most countries, in a Spectrum management process known as frequency allocation or spectrum allocation. Radio propagation does not stop at national boundaries...
s. (There can be gaps between channels, where numbers are sequential, but frequencies are not contiguous, such as the skip from VHF low to high, and the jump to UHF.) On cable TV, it is possible to use
adjacent channelIn broadcasting an adjacent channel is an AM, FM, or TV channel that is next to another channel. First-adjacent is immediately next to another channel, second-adjacent is two channels away, and so forth. Information on adjacent channels is used in keeping stations from interfering with one...
s only because they are all at the same power, something which could only be done over the air if the two stations were transmitted at the same
powerIn radio telecommunications, effective radiated power or equivalent radiated power is a standardized theoretical measurement of radio frequency energy using the SI unit watts, and is determined by subtracting system losses and adding system gains...
and height from the same location. For digital TV, selectivity is inherently better, therefore channels adjacent (either to analog or digital stations) can be used even in the same
areaA media market, broadcast market, media region, designated market area , Television Market Area , or simply market is a region where the population can receive the same television and radio station offerings, and may also include other types of media including newspapers and Internet content...
.
Other meanings
Commonly, the term "television channel"
is used to refer toMetonymy is a figure of speech used in rhetoric in which a thing or concept is not called by its own name, but by the name of something intimately associated with that thing or concept...
either a
terrestrial televisionTerrestrial television is a mode of television broadcasting which does not involve satellite transmission or cables — typically using radio waves through transmitting and receiving antennas or television antenna aerials...
station or its
cableCable television is a system of providing television programs to consumers via radio frequency signals transmitted to televisions through coaxial cables or digital light pulses through fixed optical fibers located on the subscriber's property, much like the over-the-air method used in traditional...
/
satelliteSatellite television is television programming delivered by the means of communications satellite and received by an outdoor antenna, usually a parabolic mirror generally referred to as a satellite dish, and as far as household usage is concerned, a satellite receiver either in the form of an...
counterpart (both outlined below). Sometimes, especially outside the U.S. and in the context of cable/satellite television, it is used instead of the term
television networkA television network is a telecommunications network for distribution of television program content, whereby a central operation provides programming to many television stations or pay TV providers. Until the mid-1980s, television programming in most countries of the world was dominated by a small...
, which otherwise (in its technical use above) describes a group of geographically-distributed television stations that share
affiliationIn the broadcasting industry , a network affiliate is a local broadcaster which carries some or all of the television program or radio program line-up of a television or radio network, but is owned by a company other than the owner of the network...
/ownership and some or all of their programming with one another.
This terminology may be muddled somewhat in other
jurisdictionJurisdiction is the practical authority granted to a formally constituted legal body or to a political leader to deal with and make pronouncements on legal matters and, by implication, to administer justice within a defined area of responsibility...
s, for instance
EuropeEurope is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, where terrestrial channels are commonly mapped from physical channels to common numerical positions (i.e.
BBC OneBBC One is the flagship television channel of the British Broadcasting Corporation in the United Kingdom. It was launched on 2 November 1936 as the BBC Television Service, and was the world's first regular television service with a high level of image resolution...
does not broadcast on any particular "channel 1" but is nonetheless mapped to the "1" input on most British television sets). On digital platforms, such (location) channels are usually arbitrary and changeable, due to
virtual channelIn telecommunications, a logical channel number , also known as virtual channel, is a channel designation which differs from that of the actual radio channel on which the signal travels....
s.
Television station
A television station is a type of broadcast station that
broadcastBroadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...
s both
audioSound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
and videoVideo is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
to
televisionTelevision is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
receiverA radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
s in a particular area. Traditionally, TV stations made their broadcasts by sending specially-encoded
radioRadio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
signals over the air, called
terrestrial televisionTerrestrial television is a mode of television broadcasting which does not involve satellite transmission or cables — typically using radio waves through transmitting and receiving antennas or television antenna aerials...
. Individual television stations are usually granted
licenseThe verb license or grant licence means to give permission. The noun license or licence refers to that permission as well as to the document recording that permission.A license may be granted by a party to another party as an element of an agreement...
s by a
government agencyA government or state agency is a permanent or semi-permanent organization in the machinery of government that is responsible for the oversight and administration of specific functions, such as an intelligence agency. There is a notable variety of agency types...
to use a particular section of the
radio spectrumRadio spectrum refers to the part of the electromagnetic spectrum corresponding to radio frequencies – that is, frequencies lower than around 300 GHz ....
(a
channelIn telecommunications and computer networking, a communication channel, or channel, refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel...
) through which they send their signals. Some stations use LPTV broadcast translators to
retransmitA repeater is an electronic device that receives asignal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.-Description:...
to further areas.
Many television stations are now in the process of converting from analogue (
NTSCNTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
,
PALPAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
or
SECAMSECAM, also written SÉCAM , is an analog color television system first used in France....
) to digital TV (ATSC, DVB or ISDB).
Non-broadcast television channels
Because some regions have had difficulty picking up
over-the-airTerrestrial television is a mode of television broadcasting which does not involve satellite transmission or cables — typically using radio waves through transmitting and receiving antennas or television antenna aerials...
signals (particularly in
mountainImage:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...
ous areas), alternative means of distribution such as direct-to-home satellite and cable television have been introduced. Television channels specifically built to run on cable or satellite blur the line between TV station and TV network. That fact led some early cable channels to call themselves
superstationSuperstation in United States television can have several meanings. In its most precise meaning, a superstation is defined by the Federal Communications Commission as "A television broadcast station, other than a network station, licensed by the FCC that is secondarily transmitted by a satellite...
s.
Satellite and cable have created changes.
Local programmingThe term Local Programme, Local Programming, Local Content or Local Television refers to a television programme made by a television station or independent television producer for broadcast only within the station's transmission area or television market...
TV stations in an area can
sign-upRetransmission consent is an option granted to US television stations as part of the law that granted such stations the option to elect must-carry rights. Under retransmission consent, a full-power US television station may elect to negotiate with a cable system operator for carriage of its...
or even
be requiredIn cable television, governments apply a must-carry regulation stating that locally-licensed television stations must be carried on a cable provider's system.- Canada :...
to be carried on cable, but content providers like TLC cannot. They are not licensed to run broadcast equipment like a station, and they do not regularly provide content to licensed broadcasters either. Furthermore, a distributor like
TNTTurner Network Television is an American cable television channel created by media mogul Ted Turner and currently owned by the Turner Broadcasting System division of Time Warner...
may begin producing its own programming, and shows presented exclusively on cable/satellite by one distributor may be
syndicatedIn broadcasting, syndication is the sale of the right to broadcast radio shows and television shows by multiple radio stations and television stations, without going through a broadcast network, though the process of syndication may conjure up structures like those of a network itself, by its very...
to broadcast stations. The cost of creating a nationwide channel has been reduced and there has been a huge increase in the number of such channels, with most catering to a small group. See also:
significantly viewedSignificantly viewed are television stations determined by the Federal Communications Commission to be local stations that have a significant viewership outside of their Nielsen designated market area...
.
From the definitions above, use of the terms "network" or "station" in reference to nationwide cable/satellite channels is technically inaccurate. However, this is an arbitrary, inconsequential distinction, and varies from company to company. Indeed, the term "
cable networkA cable channel is a television channel available via cable television. Such channels are usually also available via satellite television, including direct broadcast satellite providers such as DirecTV, Dish Network and BSkyB...
" has entered into common usage in the United States in reference to such channels. There is even some geographical separation among "national" cable/satellite channels in the U.S., be it programming (e.g., the
Fox Sports NetThe Fox Sports Regional Networks, or simply Fox Sports Net , are a collection of cable TV regional sports networks in the United States owned and operated by News Corporation.- Beginnings :...
group of regional sports channels, which share several programs), or simply regionalized advertising inserted by the local cable company.
Should a legal distinction be necessary between a (location) channel as defined above and a television channel in this sense, the terms "programming service" (e.g.
http://arbiter.wipo.int/domains/decisions/html/2001/d2001-1440.html) or "programming undertaking" (for instance,
http://www.crtc.gc.ca/Eng/forms/efiles/f109.htm) may be used instead for the latter definition.
A person viewing by cable or satellite might not know what kind of organization is responsible for a given program, especially if it is syndicated, so what seems to be a station or a network may be neither.
See also
- Barker channel
A barker channel is a form of electronic media known as digital signage. It is a TV channel that is entirely composed of sales promotion and advertising, usually marketing various features of the service carrying the channel...
- Lists of television channels
- Television channel frequencies
The following tables show the frequencies assigned to broadcast television channels in various regions of the world, along with the ITU letter designator for the system used. The frequencies shown are for the video and audio carriers. The channel itself occupies several megahertz of bandwidth....