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In broadcasting, digital subchannels are a method of transmitting more than one independent program stream simultaneously from the same
digital radio Digital radio is the use of digital technology to transmit or receive across the radio spectrum. Digital transmission by radio waves includes digital broadcasting, and especially digital audio radio services. Types In digital broadcasting syst ...
or
television Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertisin ...
station Station may refer to: Agriculture * Station (Australian agriculture), a large Australian landholding used for livestock production * Station (New Zealand agriculture), a large New Zealand farm used for grazing by sheep and cattle ** Cattle statio ...
on the same
radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the upp ...
channel. This is done by using data compression techniques to reduce the size of each individual program stream, and
multiplexing In telecommunications and computer networking, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource - a ...
to combine them into a single signal. The practice is sometimes called "
multicasting In computer networking, multicast is group communication where data transmission is addressed to a group of destination computers simultaneously. Multicast can be one-to-many or many-to-many distribution. Multicast should not be confused with ...
".


ATSC television


United States

The
ATSC Advanced Television Systems Committee (ATSC) standards are an American set of standards for digital television transmission over terrestrial, cable and satellite networks. It is largely a replacement for the analog NTSC standard and, like that ...
digital television standard used in the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
supports multiple program streams over-the-air, allowing
television station A television station is a set of equipment managed by a business, organisation or other entity, such as an amateur television (ATV) operator, that transmits video content and audio content via radio waves directly from a transmitter on the earth ...
s to transmit one or more subchannels over a single digital signal. A
virtual channel In most telecommunications organizations, a virtual channel is a method of remapping the ''program number'' as used in H.222 Program Association Tables and Program Mapping Tables to a channel number that can be entered via digits on a receiver's ...
numbering scheme distinguishes broadcast subchannels by appending the
television channel A television channel is a terrestrial frequency or virtual number over which a television station or television network is distributed. For example, in North America, "channel 2" refers to the terrestrial or cable band of 54 to 60 MHz, with ...
number with a period digit (".xx"). Simultaneously, the suffix indicates that a television station offers additional programming streams. By convention, the suffix position ".1" is normally used to refer to the station's main digital channel and the ".0" position is reserved for analog channels. For example, most of the
owned-and-operated station In the broadcasting industry, an owned-and-operated station (frequently abbreviated as an O&O) usually refers to a television or radio station owned by the network with which it is associated. This distinguishes such a station from an affiliate ...
s/ affiliates of Trinity Broadcasting Network transmit five streams in the following format: The most of any large broadcaster in the United States, Ion Television stations transmit nine channels (in standard definition) and the Katz Broadcasting subchannel services
Court TV Court TV is an American digital broadcast network and former cable television channel. It was originally launched in 1991 with a focus on crime-themed programs such as true crime documentary series, legal analysis talk shows, and live news cove ...
, Ion Mystery,
Bounce TV Bounce TV is an American digital multicast television network owned by Katz Broadcasting, a subsidiary of E. W. Scripps Company. Promoted as "the first 24/7 digital multicast broadcast network created to target African Americans", the channel fe ...
,
Laff Laff (legal name: Laff Media, LLC) is an American digital multicast television network headquartered in Atlanta, Georgia and is owned by the Katz Broadcasting subsidiary of the E. W. Scripps Company. The network specializes in comedy programmi ...
, Grit, TrueReal, Defy TV, and
Newsy Newsy is an American news network headquartered in Atlanta, Georgia, and owned by the E. W. Scripps Company. Its content is available for free on OTT platforms including Pluto TV (which inserts short-form ''Newsy Briefs'' into commercial breaks ...
. More programming streams can be fit into a single channel space at the cost of broadcast quality. Among smaller stations, KAXT-CD in
San Francisco San Francisco (; Spanish language, Spanish for "Francis of Assisi, Saint Francis"), officially the City and County of San Francisco, is the commercial, financial, and cultural center of Northern California. The city proper is the List of Ca ...
is believed to have the most feeds of any individual over-the-air broadcaster, offering twelve video and several audio feeds (all transmitted in standard definition).
WANN-CD WANN-CD, virtual channel 32 (UHF digital channel 20), is a low-powered, Class A television station licensed to Atlanta, Georgia Atlanta ( ) is the capital and most populous city of the U.S. state of Georgia. It is the seat of Fulton C ...
in
Atlanta, Georgia Atlanta ( ) is the capital and most populous city of the U.S. state of Georgia. It is the seat of Fulton County, the most populous county in Georgia, but its territory falls in both Fulton and DeKalb counties. With a population of 498,715 ...
, with ten video and ten audio feeds, comes at a close second. Several cable-to-air broadcasters, such as those in Willmar, Minnesota and
Cortez, Colorado Cortez () is a home rule municipality that is the county seat and the most populous municipality of Montezuma County, Colorado, United States. The city population was 8,766 at the 2020 United States Census. History In 1886, the town was built t ...
, have multiplexed more than five separate
cable television Cable television is a system of delivering television programming to consumers via radio frequency (RF) signals transmitted through coaxial cables, or in more recent systems, light pulses through fibre-optic cables. This contrasts with broa ...
channels into subchannels of one signal. Operating in a sector traditionally lacking subchannels, digital cable television provider Music Choice packages its nearly 50 music channels (including
Music Choice Play Music Choice (abbreviated as MC) is an American television music service that digitally broadcasts audio-based music channels and video-related content to cable television providers in the United States. Music Choice reaches 65 million househol ...
) as digital subchannels of one channel. This is possible as the only information sent over each channel are audio feeds and a still slide which rotates every 20 seconds, displaying an advertisement and information about the current playing song on the individual channel. The audio feed and rotating stills occupy significantly less bandwidth than video feeds, leaving space for more multiplexed content. A broadcaster saves significant costs in power and bandwidth through multiplexing in comparison to the cost of operating additional analog television stations to accommodate the extra programming. In practice, operating extra stations is impossible due to the required channel and distance separations combined with the available number of channels. Most ATSC tuners will automatically add a new digital subchannel to their internal
channel map In most telecommunications organizations, a virtual channel is a method of remapping the ''program number'' as used in H.222 Program Association Tables and Program Mapping Tables to a channel number that can be entered via digits on a receiver's ...
, once it is tuned to the station carrying the new channel. However, some of these will not delete the channel if the station removes it.
Mobile DTV Mobile television is television watched on a small handheld or mobile device. It includes service delivered via mobile phone networks, received free-to-air via terrestrial television stations, or via satellite broadcast. Regular broadcast stand ...
is also carried on ATSC stations, but as a separate service, according to the ATSC-M/H standard. The
Federal Communications Commission The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdiction ...
(FCC) considers all subchannels carried by a single station to have the same call letters for legal
identification Identification or identify may refer to: *Identity document, any document used to verify a person's identity Arts, entertainment and media * ''Identify'' (album) by Got7, 2014 * "Identify" (song), by Natalie Imbruglia, 1999 * Identification ( ...
purposes. However, within the broadcast sales industry, to differentiate subchannels, the initial letter of a call sign changes per subchannel.


Canada

Although digital television services in Canada use the same ATSC technology as the United States, none of the stations currently broadcasting a digital signal transmit any subchannel other than a possible HD service or a standard definition simulcast of the main channel. Unlike the FCC in the United States, the body that governs Canadian broadcasting licenses, the
Canadian Radio-television and Telecommunications Commission The Canadian Radio-television and Telecommunications Commission (CRTC; french: Conseil de la radiodiffusion et des télécommunications canadiennes, links=) is a public organization in Canada with mandate as a regulatory agency for broadcasti ...
(CRTC), requires stations to file license amendments in order to be considered for permission to carry digital subchannels (this differs from the Commission's rules for premium cable television services, which allow the addition of multiplex channels consistent with the service's license requirements without the need to amend the license). On August 17, 2012, the CRTC gave approval to
Leamington, Ontario Leamington ( ) is a municipality in Essex County, Ontario, Canada. With a population of 27,595 in the Canada 2016 Census, it forms the second largest urban centre in Windsor-Essex County after Windsor, Ontario. It includes Point Pelee National P ...
community station CFTV-TV to broadcast four local subchannels on its digital signal, making it the first station in Canada to launch original content on its multiplex channels.


Mexico

Some Mexican TV stations use digital subchannels as they are used in the United States. The
Sistema Público de Radiodifusión del Estado Mexicano The ''Sistema Público de Radiodifusión del Estado Mexicano'' (Mexican State Public Broadcasting System, abbreviated SPR) until 2014, is an independent Mexican government agency. Its mission is to support the development of public broadcasting ...
, a public broadcaster, operates 26 multiplexed transmitters throughout Mexico carrying five to six public television services, while XHTRES-TDT carries Imagen Radio audio on a subchannel. One notable experiment involving digital subchannels in Mexico was undertaken by
TV Azteca TV Azteca, S.A.B. de C.V. is a Mexican multimedia conglomerate owned by Grupo Salinas. It is the second-largest mass media company in Mexico after Televisa. It primarily competes with Televisa as well as some local operators. It owns two national ...
, which used its three muxes in the Mexico City area to broadcast a service called Hi-TV, featuring several channels encoded in H.264 MPEG-4 encoding, which while available in the ATSC standard is not common on TV sets. This use of subchannels as pseudo-restricted signals within non-restricted channels was placed under investigation and litigation with authorities at COFETEL (the Federal Teleommunications Commission), involving a fine of 4,453,150
Mexican peso The Mexican peso (Currency symbol, symbol: $; ISO 4217, code: MXN) is the currency of Mexico. Modern peso and dollar currencies have a common origin in the 16th–19th century Spanish dollar, most continuing to use dollar sign, its sign, "$". ...
s. HiTV subchannels began broadcasting on an intermittent basis in 2013 and were almost completely deactivated in late 2014.
Televisa Grupo Televisa is a Mexican multimedia mass media company. A major Latin American mass media corporation, it often presents itself as the largest producer of Spanish-language content. In April 2021, Televisa and Univision Communications announce ...
and TV Azteca use subchannels in rural areas in order to ensure national network service. As a result, since 2016, many areas that formerly had only one Azteca or Televisa network now have both from the same transmitter. Additionally, TV Azteca has two national services that are broadcast as subchannels in most areas, a+ and adn40. In October 2016, the
IFT IFT may refer to: * "I.F.T." (''Breaking Bad''), an episode of ''Breaking Bad'' * Federal Telecommunications Institute ( es, Instituto Federal de Telecomunicaciones, link=no), a government agency of Mexico * Implicit function theorem * Independen ...
put into effect new guidelines for the numbering of virtual channels. As a result, national networks use consistent numbers nationwide; SPR transmitters now use four or five major channel numbers (11, 14, 20, 22, and 45 in some areas). Prior to this, digital television stations usually used virtual channels corresponding to their former analog positions, still the case for certain local stations. The IFT enforces minimum bitrates for digital television channels, and as such it is not possible for a station to broadcast two HD feeds in MPEG-2 encoding. Most HD feeds are provided in 1080i with all subchannels in 480i standard definition.


DVB television


Australia

Australian digital subchannels are currently divided between high definition (HD), standard definition (SD) and radio subchannels (the latter type is only carried by the stations of
non-commercial A non-commercial (also spelled noncommercial) activity is an activity that does not, in some sense, involve commerce, at least relative to similar activities that do have a commercial objective or emphasis. For example, advertising-free community ...
networks SBS Television and
ABC Television ABC Television most commonly refers to: *ABC Television Network of the American Broadcasting Company, United States, or *ABC Television (Australian TV network), a division of the Australian Broadcasting Corporation, Australia ABC Television or ABC ...
). Each network currently has at least one HD sub channel. All networks use their HD subchannel to provide a simulcast of their primary channel or their multichannels. Inclusive of their primary standard definition channels (ignoring HD): * SBS Television offers three unique SD subchannels (
SBS Food SBS Food is an Australian free-to-air television channel owned and operated by the Special Broadcasting Service (SBS). The channel airs programs about food and cooking, from cultures around the world. History SBS first revealed it would launc ...
, NITV and SBS WorldWatch) and a HD simulcast of its primary channel (
SBS HD SBS is a national public television network in Australia. Launched on 24 October 1980, it is the responsibility of SBS's television division, and is available nationally. In 2018, SBS had a 7.7% audience share. As of 2022, SBS is the lowest ...
); as well as it’s SBS Viceland and SBS World Movies channels with no SD simulcasts. * ABC Television offers three unique SD subchannels ( ABC TV Plus/ ABC Kids, ABC Me, and
ABC News ABC News is the news division of the American broadcast network ABC. Its flagship program is the daily evening newscast ''ABC World News Tonight, ABC World News Tonight with David Muir''; other programs include Breakfast television, morning ...
) and a HD simulcast of its primary channel ( ABC HD). * The Seven Network offers three unique SD subchannels ( 7two,
7mate 7mate is an Australian free-to-air digital television multichannel, which was launched by the Seven Network on 25 September 2010. The channel contains sport and regular programs aimed primarily to a male audience, with programming drawn from a c ...
and 7flix), a
datacasting Datacasting (data broadcasting) is the broadcasting of data over a wide area via radio waves. It most often refers to supplemental information sent by television stations along with digital terrestrial television (DTT), but may also be applied ...
channel (
Racing.com Racing.com (stylised as RACING.COM) is an Australian free-to-air standard-definition digital television channel, owned and operated by the Seven Network and Racing Victoria. The channel broadcasts live Victorian and South Australian horse racing ...
) and a HD simulcast of its primary channel (
7HD 7HD is an Australian television channel, owned by Seven West Media, originally launched on 15 October 2007 featuring unique breakaway programming from 10 December 2007 to 4 October 2009 and a HD simulcast of Seven until 25 September 2010. The ...
) as well as it’s 7two and 7mate channels. ( 7mate HD, 7two HD). * The Nine Network offers four unique SD subchannels ( 9Go!, 9Rush, 9Gem and 9Life), a datacasting channel ( Extra) and a HD simulcast of its primary channel (
9HD 9HD is an Australian television channel owned by Nine Entertainment, originally launched on 17 March 2008 featuring unique "breakaway" programming until 2009 and a high-definition simulcast of the Nine Network from 2009 to 2010 and again sin ...
) as well as a HD simulcast of its 9Gem channel. * Network 10 offers two unique SD subchannels (
10 Peach 10 Peach is an Australian free-to-air television channel operated by Network 10. It was launched on 11 January 2011 as Eleven. It is owned by ElevenCo, which was established as a joint venture between Ten Network Holdings and CBS Studios Inter ...
, and
10 Shake 10 Shake is an Australian free-to-air digital television multichannel owned by Network 10. It launched on 27 September 2020 at 6am. The channel includes a mix of shows for people aged forty and under. It broadcasts programming for children fro ...
), two datacasting channels ( TVSN and Gecko TV) and a HD simulcast of its primary channel (
10 HD 10 HD is an Australian free-to-air television channel that was originally launched on 16 December 2007 on channel 1. The channel was available to high definition digital television viewers through Network 10 owned-and-operated stations. The ...
) as well as their
10 Bold 10 Bold is an Australian free-to-air digital television multichannel owned by Network 10. It originally launched on 26 March 2009 as One HD with a focus on broadcasting sports-based programming and events, but rebranded to One in April 2011 to ...
channel with no SD simulcast. Community television stations in
Melbourne Melbourne ( ; Boonwurrung/Woiwurrung: ''Narrm'' or ''Naarm'') is the capital and most populous city of the Australian state of Victoria, and the second-most populous city in both Australia and Oceania. Its name generally refers to a met ...
( C31) and
Adelaide Adelaide ( ) is the capital city of South Australia, the state's largest city and the fifth-most populous city in Australia. "Adelaide" may refer to either Greater Adelaide (including the Adelaide Hills) or the Adelaide city centre. The dem ...
( C44) also broadcast digital signals, however they typically only broadcast a single SD subchannel which simulcasts that station's primary channel. There have been a number of issues surrounding the introduction of digital subchannels in Australia. The first subchannels launched by the ABC – ABC Kids and Fly TV – closed after less than two years in operation in 2003 as a reaction to budget cuts by the conservative Howard Government under Communications Minister Alston and low viewership (partly due to the limited distribution of set-top boxes); and commercial broadcasters could not legally air a digital subchannel other than a single high-definition service until 2009.


Europe

As most digital services in
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
rely on more complex methods of multiplexing, where a large number of digital channels by many different broadcasters can be broadcast on one single frequency, the concept of a subchannel is instead applied to the variety of channels that are produced by a single company. This can vary widely depending on the country: for example,
ITV ITV or iTV may refer to: ITV *Independent Television (ITV), a British television network, consisting of: ** ITV (TV network), a free-to-air national commercial television network covering the United Kingdom, the Isle of Man, and the Channel Islan ...
currently has four of its digital channels ( ITV1,
ITV2 ITV2 is a British free-to-air television channel owned by ITV Digital Channels, a division of ITV plc. It was launched on 7 December 1998. For a number of years, it had the largest audience share after the five analogue terrestrial stations, a ...
,
ITV3 ITV3 is a British free-to-air television channel owned by ITV Digital Channels, a division of ITV plc. The channel was first launched on Monday 1 November 2004 at 9pm, replacing Plus (Granada). ITV3 is the sixth-largest UK television channel by ...
and
ITV4 ITV4 is a Television in the United Kingdom, British free-to-air television channel which was launched on 1 November 2005. It is owned by ITV Digital Channels, a division of ITV plc, and is part of the ITV (TV network), ITV network. The channel h ...
) broadcasting on one multiplexed service, while two others ( ITV2 +1 and CITV) are each broadcast on another, separate multiplex.


ISDB television

In
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
and
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
,
ISDB Integrated Services Digital Broadcasting (ISDB; Japanese language, Japanese: , ''Tōgō dejitaru hōsō sābisu'') is a Japanese broadcasting standard for digital television (DTV) and digital radio. ISDB supersedes both the NTSC-J analog telev ...
(similar to the DVB format) is used, and was specifically designed with physical RF segments that could be split to use for different subchannels. In Brazil, a digital subchannel is only allowed to the public and educational stations.


Tradeoffs

As the amount of data which can be carried on one digital television channel at one time is limited, the addition of multiple channels of programming as digital subchannels comes at the expense of having less available bandwidth for other purposes, such as the ability to transmit
high definition High definition or HD may refer to: Visual technologies *HD DVD, discontinued optical disc format *HD Photo, former name for the JPEG XR image file format *HDV, format for recording high-definition video onto magnetic tape * HiDef, 24 frames-pe ...
content. A station carrying multiple subchannels will normally limit itself to one high-definition channel (or in some cases, two HD channels), with any additional channels being carried in standard definition. Because of the tradeoffs, stations owned by
CBS Corporation The second incarnation of CBS Corporation (the first being a short-lived rename of the Westinghouse Electric Corporation) was an American multinational media conglomerate with interests primarily in commercial broadcasting, publishing, and t ...
through its
CBS Television Stations CBS News and Stations (formerly CBS Television Stations) is a division of the CBS Entertainment Group unit of Paramount Global that owns and operates a group of American television stations. , Paramount owns 28 stations, broken down as follows: ...
subsidiary (which include
owned-and-operated station In the broadcasting industry, an owned-and-operated station (frequently abbreviated as an O&O) usually refers to a television or radio station owned by the network with which it is associated. This distinguishes such a station from an affiliate ...
s of CBS and
The CW ''The'' () is a grammatical article in English, denoting persons or things already mentioned, under discussion, implied or otherwise presumed familiar to listeners, readers, or speakers. It is the definite article in English. ''The'' is the m ...
, and some independent stations) generally opted not to carry digital subchannels and transmitted only a 1080i high definition main feed; this changed in 2013 with the addition of dedicated local news channels on CBS O&Os in
New York City New York, often called New York City or NYC, is the List of United States cities by population, most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the L ...
and
Philadelphia Philadelphia, often called Philly, is the largest city in the Commonwealth of Pennsylvania, the sixth-largest city in the U.S., the second-largest city in both the Northeast megalopolis and Mid-Atlantic regions after New York City. Sinc ...
(the company later announced the creation of Decades, a multicast network part-owned by CBS which aired on all CBS and CW owned-and-operated stations from 2015 to 2018). It is possible for stations to carry more than two subchannel feeds in HD, at least nominally. Actual picture quality may be comparable to DVD video. Some examples of stations broadcasting in this format are: Outside the United States – especially in Europe – high-definition feeds are rarer, and most countries only provide a single high-definition service for each broadcaster. For example, in
France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
, there are only five HD services: one each for
TF1 TF1 (; standing for ''Télévision Française 1'') is a French commercial television network owned by TF1 Group, controlled by the Bouygues conglomerate. TF1's average market share of 24% makes it the most popular domestic network. TF1 is par ...
, France 2, Canal+, M6 and Arte; in the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
, four HD services are currently transmitted over terrestrial frequencies:
BBC One HD BBC One is a British free-to-air public broadcast television network owned and operated by the BBC. It is the corporation's flagship network and is known for broadcasting mainstream programming, which includes BBC News television bulletins, p ...
, BBC Two HD, ITV HD and
Channel 4 HD Channel 4 is a British free-to-air public broadcast television network operated by the state-owned Channel Four Television Corporation. It began its transmission on 2 November 1982 and was established to provide a fourth television service i ...
(
S4C Clirlun S4C (, ''Sianel Pedwar Cymru'', meaning ''Channel Four Wales'') is a Welsh language free-to-air public broadcast television channel. Launched on 1 November 1982, it was the first television channel to be aimed specifically at a Welsh-speaking ...
is broadcast in Wales instead of Channel 4 HD).


Television applications


Commercial networks

In the United States, digital subchannels have been used to provide programming from multiple major networks on a single television station. This has become prevalent since the late 2000s in smaller
markets Market is a term used to describe concepts such as: * Market (economics), system in which parties engage in transactions according to supply and demand * Market economy *Marketplace, a physical marketplace or public market Geography *Märket, a ...
that have as few as one or two commercial stations, which during the era of analog television, would not have been able to carry the complete programming lineups of all four major commercial networks (CBS, NBC, ABC and Fox) because of the station's own local and syndicated programming commitments, and overlapping network programs that would be tough to schedule outside of regular timeslots. A prime example is the Wheeling, West Virginia/ Steubenville, Ohio market, which for decades was home to only two stations (CBS affiliate WTRF-TV and NBC affiliate
WTOV-TV WTOV-TV (channel 9) is a television station licensed to Steubenville, Ohio, United States, serving the Wheeling, West Virginia–Steubenville, Ohio market as an affiliate of NBC and Fox. Owned by Sinclair Broadcast Group, the station maintains s ...
; the cable-only WBWO also served the market as a WB and now as a CW affiliate) and had to mostly rely on stations in
Pittsburgh Pittsburgh ( ) is a city in the Commonwealth (U.S. state), Commonwealth of Pennsylvania, United States, and the county seat of Allegheny County, Pennsylvania, Allegheny County. It is the most populous city in both Allegheny County and Wester ...
(and to a lesser extent
Columbus Columbus is a Latinized version of the Italian surname "''Colombo''". It most commonly refers to: * Christopher Columbus (1451-1506), the Italian explorer * Columbus, Ohio, capital of the U.S. state of Ohio Columbus may also refer to: Places ...
and
Youngstown, Ohio Youngstown is a city in the U.S. state of Ohio, and the largest city and county seat of Mahoning County, Ohio, Mahoning County. At the 2020 United States census, 2020 census, Youngstown had a city population of 60,068. It is a principal city of ...
) to view programming from other networks. However, the advent of digital television allowed WTRF to launch two digital channels (one as a primary Fox/secondary MyNetworkTV affiliate, the other affiliated with ABC) while still carrying CBS programming in full on its main signal (WTOV later took the Fox affiliation for its second subchannel in September 2014). Upon their launches in September 2006, The CW and MyNetworkTV were among the first conventional networks to actively utilize subchannel-only affiliations in markets where a standalone station is not available to affiliate with; this is particularly true of The CW's small-market feed,
The CW Plus The CW Plus is a secondary national programming service feed of The CW that is fully controlled and 75% owned by Nexstar Media Group, with Paramount Global and Warner Bros. Discovery each owning a 12.5% stake in the network. It is intended primar ...
, which originally consisted mostly of cable-only affiliations (by way of inheriting the model and much of the affiliate body of predecessor
The WB 100+ Station Group The WB 100+ Station Group (originally called The WeB from its developmental stages until March 1999) was a national programming service of The WB—owned by the Warner Bros. Entertainment division of Time Warner, the Tribune Company, and group fo ...
). Since its launch, affiliates of other major networks have taken over the operations of cable-only CW Plus affiliates (or even outright replacing WB 100+ cable channels at the launch of The CW) and began transmitting the service over subchannels to reach viewers who do not subscribe to a pay television service. Some Spanish language networks (such as Azteca America,
Estrella TV Estrella TV () is an American Spanish-language broadcast television network owned by the Estrella Media subsidiary of HPS Investment Partners, LLC. The network primarily features programs, the vast majority of which are produced by the network ...
and
Telemundo Telemundo (; formerly NetSpan) is an American Spanish-language Terrestrial television, terrestrial television network owned by NBCUniversal Television and Streaming#NBCUniversal Telemundo Enterprises, NBCUniversal Telemundo Enterprises, a divi ...
) have also been carried on digital subchannels, either as subchannel-exclusive services or to provide programming to markets where a main channel affiliation may not be available. Other stations have launched subchannels with an independent station format on their DT2 signals (such as WTTV in
Indianapolis Indianapolis (), colloquially known as Indy, is the state capital and most populous city of the U.S. state of Indiana and the seat of Marion County. According to the U.S. Census Bureau, the consolidated population of Indianapolis and Marion ...
,
Indiana Indiana () is a U.S. state in the Midwestern United States. It is the 38th-largest by area and the 17th-most populous of the 50 States. Its capital and largest city is Indianapolis. Indiana was admitted to the United States as the 19th s ...
– a market with enough commercial stations able to support affiliations with all six networks and a standalone independent, although the seventh (WTTK) instead acts as a WTTV
satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotope ...
– which converted its 4.2 subchannel as an independent station in January 2015 as a result of owner
Tribune Media Tribune Media Company, also known as Tribune Company, was an American multimedia conglomerate headquartered in Chicago, Illinois. Through Tribune Broadcasting, Tribune Media was one of the largest television broadcasting companies, owning 39 ...
selling the local rights to the CW affiliation that was to move from its main feed on 4.1 to
WISH-TV WISH-TV (channel 8) is a television station in Indianapolis, Indiana, United States, affiliated with The CW. It is locally owned by Circle City Broadcasting alongside Marion-licensed MyNetworkTV affiliate WNDY-TV (channel 23) and low-power, C ...
, whose CBS affiliation was assumed by WTTV). Digital subchannels are also used to relay stations beyond their traditional signal coverage areas to reach an entire market. In the Upper Peninsula of
Michigan Michigan () is a state in the Great Lakes region of the upper Midwestern United States. With a population of nearly 10.12 million and an area of nearly , Michigan is the 10th-largest state by population, the 11th-largest by area, and the ...
and northern
Minnesota Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the 22nd most populous, with over 5.75 million residents. Minnesota is home to western prairies, now given over to ...
, many of these stations are on duplicate frequencies to cover a large market area. This is used to duplicate network service for stations that are part of duopolies, where transmitters scattered through a large geographical area allow multiple networks and channels to be carried. The most prominent example is the
Granite Broadcasting Corporation Granite Broadcasting Limited liability company, LLC is a broadcasting holding company in New York City which owns one television station in the United States, in Syracuse, New York. Granite was founded by W. Don Cornwell and Stuart Beck in 1988,< ...
's virtual quadropoly in
Duluth, Minnesota , settlement_type = City , nicknames = Twin Ports (with Superior), Zenith City , motto = , image_skyline = , image_caption = Clockwise from top: urban Duluth skyline; Minnesota ...
, which consists of two separate full-power stations, NBC affiliate KBJR-TV and CBS affiliate KDLH, which combined carry three subchannels (two affiliated with major networks – CW Plus affiliate "Northland CW 2" on KDLH and MyNetworkTV affiliate "My9" on KBJR – and the third, a local weather subchannel on KBJR). While KDLH carries the CW subchannel on their DT2 feed and KBJR carries the MyNetworkTV subchannel on its DT2 feed on their primary signals, all five channels are carried on satellite station KRII in Chisholm, providing the Iron Range region (located north of Duluth) programming from networks that were previously unavailable over-the-air. In the Traverse City- Cheboygan market in Upper Michigan, NBC affiliate WPBN/WTOM also simulcasts sister station WGTU/WGTQ, providing that station's ABC programming to the entire market; CBS affiliate WWTV/WWUP carries its Fox-affiliated sister WFQX/WFUP on their DT2 subchannel to expand their coverage area further north into the eastern portion of the Upper Peninsula. In many cases, these "new" channels are existing secondary channels that were carried by a low-power or Class A station or by a
cable television Cable television is a system of delivering television programming to consumers via radio frequency (RF) signals transmitted through coaxial cables, or in more recent systems, light pulses through fibre-optic cables. This contrasts with broa ...
channel. Often, the owner of a full-power television station acquires or already owns a low-power secondary station in the same market to carry another network. The use of a digital subchannel on a full-power television station as a replacement for low-power station greatly increases the available coverage area for its programming. Because of interference issues that stations transmitting on the low
VHF Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VHF ...
band (channels 2 to 6) often experience, some stations broadcasting on these frequencies are relayed on the subchannels of stations that are less prone to interference. An example of this is CBS affiliate WRGB in
Albany, New York Albany ( ) is the capital of the U.S. state of New York, also the seat and largest city of Albany County. Albany is on the west bank of the Hudson River, about south of its confluence with the Mohawk River, and about north of New York City ...
. While WRGB broadcasts its main digital on VHF channel 6 in high definition, CW-affiliated
sister station In broadcasting, sister stations or sister channels are radio or television stations operated by the same company, either by direct ownership or through a management agreement. Radio sister stations will often have different formats, and somet ...
WCWN WCWN (channel 45) is a television station licensed to Schenectady, New York, United States, serving the Capital District as an affiliate of The CW. It is owned by Sinclair Broadcast Group alongside CBS affiliate WRGB (channel 6, also licensed to ...
relays a standard-definition subchannel feed of WRGB over its digital channel 45. Since the late 2010s, some station groups have started consolidating major network affiliations onto one signal if they own the non-licensing assets of those channels. Some of this was due to the
2016 United States wireless spectrum auction The 2016 United States wireless spectrum auction, officially known as Auction 1001, allocated approximately 100 MHz of the United States Ultra High Frequency (UHF) spectrum formerly allocated to UHF television in the 600 MHz band. The spe ...
, but most have been due to companies who use sidecar companies to create virtual duopolies via
local marketing agreement In North American broadcasting, a local marketing agreement (LMA), or local management agreement, is a contract in which one company agrees to operate a radio or television station owned by another party. In essence, it is a sort of lease or tim ...
s when they are not legally able to own a duopoly outright. In the latter scenario, the station whose programming is on an LMA station is moved to a subchannel of a station that is owned outright by the ststion that own the non-licensed assets of other stations. Many companies such as
Sinclair Broadcast Group Sinclair Broadcast Group, Inc. (SBG) is a publicly traded American telecommunications conglomerate that is controlled by the descendants of company founder Julian Sinclair Smith. Headquartered in the Baltimore suburb of Cockeysville, Maryland, t ...
(via
Cunningham Broadcasting Cunningham Broadcasting Corporation is an owner of broadcast television stations in the United States. The company currently owns fifteen stations – eight affiliated with Fox, three affiliated with The CW, two affiliated with ABC, and two affili ...
,
Deerfield Media Deerfield Media, Inc. is a broadcasting company and a shell corporation owned and operated by Stephen P. Mumblow. It was established on December 1, 2012 by the acquisition of several television stations connected to the Sinclair Broadcast Group. ...
, & Howard Stirk Holdings),
Nexstar Media Group Nexstar Media Group, Inc. is an American publicly traded media company with headquarter offices in Irving, Texas; Midtown Manhattan; and Chicago, Illinois. The company is the largest television station owner in the United States, owning 197 te ...
(via Mission Broadcasting &
Vaughan Media Vaughan Media, LLC is a company which owns the broadcast licenses of several stations operated by Nexstar Media Group. History The company was founded in 2011 when it made its first acquisition, WBDT, from ACME Communications. LIN Media, the o ...
), and
Gray Television Gray Television, Inc. is an American publicly traded television broadcasting company based in Atlanta, Georgia. Founded in 1946 by James Harrison Gray as Gray Communications Systems, the company owns or operates 180 stations across the United St ...
(via
American Spirit Media American Spirit Media, LLC is a broadcasting company based in Charlotte, North Carolina. Founded by Thomas B. Henson in 2003 as Ottumwa Media Holdings, it owns television stations in several cities in the Southeastern United States. History In 2 ...
&
SagamoreHill Broadcasting SagamoreHill Broadcasting LLC is a privately held American holding company that owns 13 television stations based in the Great Lakes and southern United States regions. The company is a joint venture of the investment firm Duff Ackerman & Goodric ...
) have been doing this, partially due to regulation pressure.


Sports programming

Networks dedicated to sports programming have been launched specifically for use on digital subchannels. Until 2010, CBS affiliates often subdivided four temporary subchannels in order to show all of the early round games of the NCAA men's basketball tournament in addition to those broadcast on the main digital channel (this was superseded as a result of a new television agreement with the
NCAA The National Collegiate Athletic Association (NCAA) is a nonprofit organization that regulates student athletics among about 1,100 schools in the United States, Canada, and Puerto Rico. It also organizes the athletic programs of colleges an ...
that took effect in 2011, which gave cable networks TBS, TNT and
TruTV TruTV (stylized as truTV) is an American basic cable channel owned by Warner Bros. Discovery. The channel primarily broadcasts comedy, docusoaps and reality shows. The channel was originally launched in 1991 as Court TV, a network that focu ...
partial rights to the tournament). Most of the major professional sports leagues, however, have strict prohibitions against using subchannels for carrying multiple game broadcasts and only allow one game to be aired in a market at one time (outside of Los Angeles, where if the
Rams In engineering, RAMS (reliability, availability, maintainability and safety)Chargers The Los Angeles Chargers are a professional American football team based in the Los Angeles metropolitan area. The Chargers compete in the National Football League (NFL) as a member of the American Football Conference (AFC) West division, and ...
play at the same time, Fox is allowed to broadcast the second game on MyNetworkTV affiliate KCOP-TV, or CBS on independent
KCAL-TV KCAL-TV (channel 9) is an independent television station in Los Angeles, California, United States. It is owned by the CBS News and Stations group alongside CBS West Coast flagship KCBS-TV (channel 2). Both stations share studios at the C ...
, depending on the game's carrier that specific week); all four of the major sports leagues (the
NFL The National Football League (NFL) is a professional American football league that consists of 32 teams, divided equally between the American Football Conference (AFC) and the National Football Conference (NFC). The NFL is one of the major ...
, the
NBA The National Basketball Association (NBA) is a professional basketball league in North America. The league is composed of 30 teams (29 in the United States and 1 in Canada) and is one of the major professional sports leagues in the United St ...
,
Major League Baseball Major League Baseball (MLB) is a professional baseball organization and the oldest major professional sports league in the world. MLB is composed of 30 total teams, divided equally between the National League (NL) and the American League (AL), ...
and the
NHL The National Hockey League (NHL; french: Ligue nationale de hockey—LNH, ) is a professional ice hockey league in North America comprising 32 teams—25 in the United States and 7 in Canada. It is considered to be the top ranked professional ...
) have out-of-market sports packages that require a pay television subscription and generate significant revenue for the leagues. Most sports programming on digital subchannel broadcasters has been relegated to low-budget content such as amateur athletics, extreme sports, and hunting and fishing programming geared toward outdoorsmen, though minor league baseball,
American Hockey League The American Hockey League (AHL) is a professional ice hockey league based in the United States and Canada that serves as the primary Minor league#Ice hockey, developmental league for the National Hockey League (NHL). Since the 2010–11 AHL se ...
hockey and other minor league sports may also be seen. Prominent team sports programming on digital subchannels is rare; the general trend for sports programming tends to eschew the free-to-air model that digital subchannels use, and the cost of rights fees for most sports requires that they air on channels that air on cable and satellite television services and thus can recuperate costs through retransmission consent. Channels such as
Sportsman Channel Sportsman Channel is an American sports-oriented digital cable and satellite television network owned by the Outdoor Sportsman Group subsidiary of Kroenke Sports & Entertainment. The channel is dedicated to programming about outdoor sports, incl ...
(and the now-defunct Universal Sports) that began as digital subchannel networks now operate as cable and satellite-exclusive services. There are nonetheless a few multicast channels that have broadcast familiar sports programs:
Bounce TV Bounce TV is an American digital multicast television network owned by Katz Broadcasting, a subsidiary of E. W. Scripps Company. Promoted as "the first 24/7 digital multicast broadcast network created to target African Americans", the channel fe ...
, for instance, carried
college football College football (french: Football universitaire) refers to gridiron football played by teams of student athletes. It was through college football play that American football rules first gained popularity in the United States. Unlike most ...
from
historically black colleges and universities Historically black colleges and universities (HBCUs) are institutions of higher education in the United States that were established before the Civil Rights Act of 1964 with the intention of primarily serving the African-American community. ...
until 2013. In January 2016,
Sinclair Broadcast Group Sinclair Broadcast Group, Inc. (SBG) is a publicly traded American telecommunications conglomerate that is controlled by the descendants of company founder Julian Sinclair Smith. Headquartered in the Baltimore suburb of Cockeysville, Maryland, t ...
launched a 24-hour feed of its American Sports Network sports syndication service on subchannels of ten stations owned and/or operated by the group; the ASN multicast network was subsequently replaced by
Stadium A stadium ( : stadiums or stadia) is a place or venue for (mostly) outdoor sports, concerts, or other events and consists of a field or stage either partly or completely surrounded by a tiered structure designed to allow spectators to stand o ...
in August 2017, following the formation of a multi-platform network venture with the Chicago White Sox's Silver Chalice unit and 120 Sports.


Local and informational channels

Although not to the same level as in the late 2000s due to the population of entertainment-based multicast services, many local stations have used or currently use subchannels to carry continuous news or local weather content; in particular, there have been at least four networks that have been created to serve this audience:
NBC Weather Plus NBC Weather Plus was an American weather-oriented digital broadcast and cable television network owned as a joint venture between NBC Universal and the local affiliates of the NBC television network. The service, which was broadcast in standard d ...
(a service exclusive to NBC stations that operated from 2004 to 2008),
The AccuWeather Channel AccuWeather Inc. is an American media company that provides commercial weather forecasting services worldwide. AccuWeather was founded in 1962 by Joel N. Myers, then a Pennsylvania State University graduate student working on a master's degree i ...
, WeatherNation TV (which also maintains limited exclusive distribution on pay television services) and
TouchVision TouchVision was an American digital broadcast and internet Video on demand television network that was owned by Think Televisual. The service provided rolling news coverage that was distributed to television, mobile and tablet platforms. TouchVisi ...
. Locally programmed news subchannels (such as
News 9 Now / News on 6 Now News 9 Now and News on 6 Now are American regional digital broadcast television networks that are owned by Griffin Media. The channels simulcast and rebroadcast local news programming seen on Griffin-owned CBS affiliates KWTV-DT (channel 9) in Okl ...
on KWTV in
Oklahoma City Oklahoma City (), officially the City of Oklahoma City, and often shortened to OKC, is the capital and largest city of the U.S. state of Oklahoma. The county seat of Oklahoma County, it ranks 20th among United States cities in population, a ...
and KOTV in
Tulsa, Oklahoma Tulsa () is the second-largest city in the state of Oklahoma and 47th-most populous city in the United States. The population was 413,066 as of the 2020 census. It is the principal municipality of the Tulsa Metropolitan Area, a region with ...
or NewsChannel 5+ on
WTVF WTVF (channel 5) is a television station in Nashville, Tennessee, United States, affiliated with CBS. It is owned by the E. W. Scripps Company alongside Ion Television owned-and-operated station WNPX-TV (channel 28). WTVF's studios are located ...
in
Nashville Nashville is the capital city of the U.S. state of Tennessee and the seat of Davidson County. With a population of 689,447 at the 2020 U.S. census, Nashville is the most populous city in the state, 21st most-populous city in the U.S., and the ...
,
Tennessee Tennessee ( , ), officially the State of Tennessee, is a landlocked state in the Southeastern region of the United States. Tennessee is the 36th-largest by area and the 15th-most populous of the 50 states. It is bordered by Kentucky to th ...
) often carry rebroadcasts and simulcasts of local news programs seen on the station's main feed, in some cases displaying a ticker with news headlines and weather forecasts to provide updated information. Subchannels also allow stations to air news programs without fully pre-empting normally scheduled programing on the station's main feed. During significant
breaking news Breaking news, interchangeably termed late-breaking news and also known as a special report or special coverage or news flash, is a current issue that broadcasters feel warrants the interruption of scheduled programming or current news in orde ...
or severe weather events, for instance, a station may choose to air extended news coverage on either its main channel or a subchannel and air network programming on the other. Thus, the station can accommodate viewers wanting to watch either regular programming or news coverage. Some sports leagues, most notably the NFL, have strict rules against their game broadcasts airing on a subchannel.


Specialty programming

Since the late 2000s, entertainment-based specialty networks (also known as diginets) have been created specifically for subchannels, most commonly those dedicated to airing reruns of classic television series (such as Me-TV, Retro TV, Cozi TV and Antenna TV) and movies (such as This TV, GetTV and Movies!). Some networks (such as the African-American focused
Bounce TV Bounce TV is an American digital multicast television network owned by Katz Broadcasting, a subsidiary of E. W. Scripps Company. Promoted as "the first 24/7 digital multicast broadcast network created to target African Americans", the channel fe ...
, the female-targeted Ion Mystery and the male-targeted Grit) feature programming aimed at specific demographics. With few exceptions (such as Localish), diginets typically do not offer first-run original programming, relying on acquired content from programming distributors (most popularly, television series from the 1980s and earlier) to fill their schedules. Some stations (such as K14RK-D in Phoenix, Arizona) carry locally programmed channels offering classic television shows and music videos on their digital subchannels. With MTV's shift away from music videos since the 1990s, subchannel networks focusing entirely on music videos have also been attempted (such as The Country Network and Heartland (TV network), Heartland), however many have either been unable to gain national coverage or have lost significant market share due to various issues (for example, LIN Media, the
Sinclair Broadcast Group Sinclair Broadcast Group, Inc. (SBG) is a publicly traded American telecommunications conglomerate that is controlled by the descendants of company founder Julian Sinclair Smith. Headquartered in the Baltimore suburb of Cockeysville, Maryland, t ...
and the Journal Communications, Journal Broadcast Group terminated or opted against renewing deals with TheCoolTV between 2011 and 2013; Journal, in particular, cited TheCoolTV parent Cool Music Network, LLC's failure to pay licensing fees behind its removal of the network in a lawsuit filed against the company in 2011). Although the revenue potential is limited, many broadcasters have found subchannel-only networks to be a means of generating extra advertising revenue, as they are easily marketable to a given demographic (although they do not enjoy the same retransmission consent revenue stream from cable providers as other networks do). There have been a few notable holdouts as late as 2014 such as the Meredith Corporation (only a few of its stations have subchannels, and some of these primarily carry only local news or weather services, or in the case of WGGB-TV/Springfield, Massachusetts, allows a Fox subchannel affiliate to operate in a market with limited full-power signals traditionally beholden in the past to the Hartford, Connecticut market to the south for CBS, Fox, WB and UPN affiliates besides WGGB's ABC programming and WWLP's NBC affiliation) and the Nexstar Media Group, Nexstar Broadcasting Group (which previously used subchannels for the sole purposes of simulcasting co-owned/managed sister stations to reach an entire market or to carry programming from major networks in smaller markets, and often eliminated subchannels affiliated with multicast services following station acquisitions). Nexstar has since added multicast services such as Bounce TV and WeatherNation TV on some of its stations. Unlike the major broadcast networks, diginets carried by local stations not associated with the four major networks, The CW, and MyNetworkTV are often carried on higher cable channel placements (usually within the digital cable tiers) not readily found by most subscribers. Satellite and IPTV providers generally do not carry multicast networks unless the local station also secondarily carries a major network on that subchannel. Most diginets reach affiliation agreements with a limited number of station owners prior to launch, before expanding their national coverage through additional deals made after their debut (by comparison, Fox, The CW, MyNetworkTV and to a lesser extent, The WB and UPN, had initial station coverage reaching 60%+ of all U.S. television households through affiliation deals that were largely made before their launches, in order to have wide distribution in at least the top 100 markets). Since the majority of multicast networks are carried on major network affiliates, some full-power stations are recitant about further compressing bitrate space to fit more than one subchannel at the expense of the picture quality of their high-definition main feed. As well, in markets with fewer than six stations, available subchannel space is tighter and some multicast networks may not be able to gain affiliations especially if one of the stations uses a subchannel for the primary purpose of carrying programming from a major network (which are also often transmitted in HD, limiting bitrate space). Some networks remedy this in certain markets by affiliating with low-power stations that do not carry a major network. As of 2014, only 12 primarily subchannel-only networks reach at least 50% of all U.S. markets (with MeTV, which is available in 91% of the country — a national reach comparable to the six major commercial networks and PBS — being the largest). Diginets with wider national coverage and decent viewership are more likely to attract major advertisers, although most rely on smaller-scale advertisers such as national law firms, mortgage providers and direct response advertisers. Multicast networks often make barter deals to secure affiliations in which advertising inventory is split between the network and the station, however some networks enter into subchannel leasing deals (often if they are unable to secure sufficient cable distribution), in which the network handles the sale of advertising inventory and pays its affiliates a monthly licensing fee to carry its programming. By 2017, diginets were doing better in the ratings than some major cable networks, with MeTV being the 20th ranked broadcast network, and are also available in more homes than many cable networks. Streaming services that offer free linear channels such as Peacock (streaming service), Peacock, Pluto TV, and Stirr have also added diginets to their services, giving diginets who lack an over-the-air home in a specific market coverage. Sinclair Broadcast Group, which owns Stirr, has included its own four diginets on Stirr (Charge! (TV network), Charge!, Comet (TV network), Comet, Stadium (TV network), Stadium, & TBD (TV network), TBD), in addition to others such as the game show-themed Buzzr, which Sinclair rated as the most popular channel on Stirr.


Educational programming

Many PBS member stations around the United States broadcast their main channel in high definition and up to three standard definition subchannels; however, a few reconfigure their digital channels depending on daypart, carrying four standard definition channels during the daytime, reducing them to one HD and one SD channel at night due to technical limitations at the station's level that may prevent it from carrying PBS programming in HD full-time and maintain multiple full-time subchannels like other member stations. PBS stations often carry additional national channels such as PBS HD (PBS Satellite Service), PBS Kids, World (TV network), World, and Create (TV network), Create. In the Washington, D.C. area, MHz Networks is available as ten subchannels transmitted by two stations, with their
virtual channel In most telecommunications organizations, a virtual channel is a method of remapping the ''program number'' as used in H.222 Program Association Tables and Program Mapping Tables to a channel number that can be entered via digits on a receiver's ...
s mapped uniformally, making them appear as if they are transmitted by one station. In some U.S. states, statewide educational, cultural or Public affairs (broadcasting), public affairs services are carried on a digital subchannel of a PBS member station or network (such as the Minnesota Channel, PBS Wisconsin's Wisconsin Channel, or New York State broadcaster ThinkBright TV). The use of subchannels has also allowed educational television broadcasters to sell off former secondary PBS analogue stations to commercial broadcasting, commercial broadcasters (such as WNEQ in Buffalo, New York, Buffalo, which its sister station WNED-TV sold in 1999 to LIN Media, LIN TV (now owned by
Nexstar Media Group Nexstar Media Group, Inc. is an American publicly traded media company with headquarter offices in Irving, Texas; Midtown Manhattan; and Chicago, Illinois. The company is the largest television station owner in the United States, owning 197 te ...
) to become WNLO (TV), WNLO, now a CW affiliate), as the additional educational content these separate stations once provided can now be carried by multiple subchannels of a single parent station. Subchannels also allow some educational stations to devote an entire channel to distance education, telecourses, which are recorded by instructors and students for later use, allowing the station's main channel to air a generalized broadcast programming, schedule in the morning and Graveyard slot, overnight hours.


Temporary installations

A digital subchannel can be used to restore service from a station that has been knocked off the air due to an antenna tower collapse; the affected signal would be made available in standard-definition, or even in compressed high definition, on a subchannel of another local station, most often a competitor. ABC affiliate KATV in Little Rock, Arkansas was forced to follow this path in 2008, moving its digital signal to a subchannel of MyNetworkTV affiliate KWBF (now KARZ-TV) after a KATV tower, tower collapse knocked its main signal offline. The
virtual channel In most telecommunications organizations, a virtual channel is a method of remapping the ''program number'' as used in H.222 Program Association Tables and Program Mapping Tables to a channel number that can be entered via digits on a receiver's ...
numbering scheme allows an existing licensed broadcaster to keep its displayed channel number unchanged (in the case of KATV, PSIP channel 7) even if the signal is carried physically as a subchannel of another local station. During the Station Fire (2009), Station Fire in 2009, NBC owned-and-operated station KNBC in Los Angeles temporarily replaced programming from NBC Weather Plus, NBC Plus and Universal Sports on its subchannels with standard-definition feeds of its two Spanish language sister stations – independent station KWHY-TV (since sold to the Meruelo Group) and Telemundo owned-and-operated station KVEA – as an emergency measure in the event that the transmitters of those stations were destroyed or disabled as the fire reached Mount Wilson (California), Mount Wilson, where the transmitter facilities of most Los Angeles area stations are based.


Data, radio and non-public signals

In rare cases, digital television broadcasters have included a service known as DTV radio, in which the audio of a duopoly (broadcasting), commonly owned broadcast radio station is simulcast over a subchannel (for instance, KPJK in San Mateo, California broadcasts former FM sister KCSM (FM), KCSM on its DT3 signal).
WANN-CD WANN-CD, virtual channel 32 (UHF digital channel 20), is a low-powered, Class A television station licensed to Atlanta, Georgia Atlanta ( ) is the capital and most populous city of the U.S. state of Georgia. It is the seat of Fulton C ...
in Atlanta offers six radio stations owned by iHeartMedia, in addition to ten television channels. Non-broadcast content, pay television, subscription television channels or
datacasting Datacasting (data broadcasting) is the broadcasting of data over a wide area via radio waves. It most often refers to supplemental information sent by television stations along with digital terrestrial television (DTT), but may also be applied ...
operations unrelated to the main television programming are also permitted by the digital television standards but are less-commonly used. USDTV was an over-the-air multichannel video programming distributor, pay television service that used H.264 compression instead of standard MPEG-2. Mobile DTV now uses MPEG-4 compression, which like H.264 yields a much lower bitrate for the same video quality. For example, the Sezmi TV/DVR service uses broadcast digital subchannels (not in the clear) in selected cities to stream a limited number of "cable" channels to its subscribers for an additional fee to supplement its otherwise free digital video recorder (DVR) service allowing recordings of local broadcast channels and free and subscription internet content.


Technical considerations

Digital television supports multiple digital subchannels if the 19.39 Mbit/s (megabits per second) bitstream is divided. Therefore, station managers and broadcast engineering, broadcast engineers could run any of the following scenarios using one 6 MHz channel (note that the actual bitrate moves up and down, due to usage of variable bitrate encoding): With improvements in MPEG encoding, and tighter Variable bitrate, VBR encoding, more subchannels can be combined. 1×720p + 4×480i is becoming more common. For a frame rate of 30progressive scan, p or 60interlaced scan, i, uncompressed DTV channels have the following Bit rate, data rates in megapixels per second: For
ATSC Advanced Television Systems Committee (ATSC) standards are an American set of standards for digital television transmission over terrestrial, cable and satellite networks. It is largely a replacement for the analog NTSC standard and, like that ...
, these must be compressed into 19.4Mbit/s total per physical 6 MHz RF channel over the air, and 38.8Mbit/s for cable.


Digital radio

Various forms of
digital radio Digital radio is the use of digital technology to transmit or receive across the radio spectrum. Digital transmission by radio waves includes digital broadcasting, and especially digital audio radio services. Types In digital broadcasting syst ...
also allow for multiple program streams.


HD Radio

The primary distinguishing feature of HD Radio has been its ability to multiplex an FM broadcasting, FM radio signal. As HD Radio never achieved widespread popularity in the United States (unlike television, radio is not required to turn off its analog signals due to HD Radio being in-band on-channel and thus compatible with analog, plus the greater quantity and difficulty in signal conversion of radios compared to fixed-link television sets), its use has largely been to serve as a legal fiction. Since HD Radio was introduced in the United States in the late 2000s (decade), the FCC has allowed American broadcasters to use low-powered broadcast relay station, translators to transmit HD Radio subchannels in analog FM. This has allowed broadcasters to increase the number of programming choices available in a given media market beyond FCC limits. AM broadcasting generally lacks the bandwidth to multiplex; though in theory an AM station could transmit two separate channels using C-QUAM AM stereo, there is a limit to how far the two audio channels can be separated, and thus crosstalk is inevitable. HD Radio can be used on AM, but the bandwidth limits the digital signal to a single channel, which under FCC rules must match the analog signal. AM broadcasters have criticized the use of HD Radio on AM due to the increased adjacent-channel interference caused by the greater bandwidth it requires, with little benefit. WWFD has operated as a digital-only station with no analog signal under special temporary authority, special dispensation since 2018; in December 2019, it began testing a multiplexed digital signal with two channels. No consumer radio receivers currently have the capability to receive AM multicast signals, and thus (as with FM HD Radio) WWFD's signals have been carried on FM translators (and the Internet) to ensure continued availability. The FCC, in October 2020, concluded from WWFD's experiments: "the record does not establish that an audio stream on an HD-2 subchannel is currently technically feasible(.)"https://docs.fcc.gov/public/attachments/DOC-367361A1.pdf A proposed FCC rule would require stations that wish to multiplex their digital AM signals to request and receive permission to do so.


DAB


See also

* In-band on-channel (IBOC), digital radio technology allowing digital subchannels on FM broadcasting, FM stations * Digital Audio Broadcasting, DAB and Digital Video Broadcasting, DVB, international digital radio-television standards in use in
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
, Australia and New Zealand * QAM tuner


References

* {{DEFAULTSORT:Digital Subchannel ATSC Digital television High-definition television Television technology