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Atelevision channel, orTV channel, is aterrestrial frequency or virtual number over which a television station or television network is distributed. For example, inNorth America,channel 2 refers to the terrestrial or cable band of 54 to 60MHz, withcarrierfrequencies of 55.25 MHz forNTSC analog video (VSB) and 59.75 MHz for analog audio (FM), or 55.31 MHz for digitalATSC (8VSB). Channels may be shared by many different television stations or cable-distributed channels depending on the location and service provider.
Depending on the multinationalbandplan for a given region,analog television channels are typically 6, 7, or 8 MHz inbandwidth, and thereforetelevision channel frequencies vary as well. Channelnumbering is also different.Digital terrestrial television channels are the same as their analog predecessors forlegacy reasons, however throughmultiplexing, each physicalradio frequency (RF) channel can carry severaldigital subchannels. Onsatellites, eachtransponder normally carries one channel, however multiplesmall, independent channels can be on one transponder, with some loss ofbandwidth due to the need forguard bands between unrelatedtransmissions.ISDB, used inJapan andBrazil, has a similar segmented mode.
Preventing interference between terrestrial channels in the same area is accomplished by skipping at least one channel between two analog stations'frequency allocations. Where channel numbers are sequential, frequencies are notcontiguous, such as channel 6 to 7 skip fromVHF low to high band, and channel 13 to 14 jump toUHF. On cable TV, it is possible to useadjacent channels only because they are all at the same power, something which could only be done terrestrially if the two stations were transmitted at the samepower andheight from the samelocation. For DTT,selectivity is inherently better, therefore channels adjacent (either to analog or digital stations) can be used even in the samearea.
Commonly, the termtelevision channel is used to mean atelevision station or itspay television counterpart (both outlined below). Sometimes, especially outside the U.S. and in the context of pay television, it is used instead of the termtelevision network, which otherwise (in its technical use above) describes a group of geographically-distributed television stations that shareaffiliation/ownership and some or all of their programming with one another.This terminology may be muddled somewhat in otherjurisdictions, for instanceEurope, where terrestrial channels are commonly mapped from physical channels to common numerical positions (i.e.BBC One does not broadcast on any particularchannel 1 but is nonethelessmapped to the1 input on most British television sets). On digital platforms, such (location) channels are usually arbitrary and changeable, due tovirtual channels.
A television station is a type of terrestrial station thatbroadcasts bothaudioandvideo totelevisionreceivers in a particular area. Traditionally, TV stations made their broadcasts by sending specially-encodedradio signals over the air, calledterrestrial television. Individual television stations are usually grantedlicenses by agovernment agency to use a particular section of theradio spectrum (achannel) through which they send their signals. Some stations useLPTVbroadcast translators toretransmit to further areas.
Many television stations are now in the process of converting from analog terrestrial (NTSC,PAL orSECAM) broadcast, todigital terrestrial (ATSC broadcast,DVB orISDB).
Because some regions have had difficulty picking upterrestrial television signals (particularly inmountainous 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 themselvessuperstations.
Satellite and cable have created changes.Local programming TV stations in an area cansign-up or evenbe required to be carried on cable, but content providers likeTLC 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 likeTNT may start producing its own programming, and shows presented exclusively on pay-TV by one distributor may besyndicated to terrestrial 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.
From the definitions above, use of the termsnetwork orstation in reference to nationwide cable or satellite channels is technically inaccurate. However, this is an arbitrary, inconsequential distinction, and varies from company to company. Indeed, the termcable network has entered into common usage in the United States in reference to such channels, even with the existence ofdirect broadcast satellite. There is even some geographical separation amongnational pay television channels in the U.S., be it programming (e.g., theBally Sports 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 termsprogramming service (e.g.[1]) orprogramming undertaking (for instance,[2]) may be used instead of the latter definition.
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