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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 or
television Television (TV) is a telecommunication medium for transmitting moving images and sound. Additionally, the term can refer to a physical television set rather than the medium of transmission. Television is a mass medium for advertising, ...
station 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 u ...
channel. This is done by using
data compression In information theory, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossy or lossless. Lossless compressi ...
techniques to reduce the size of each individual program stream, and multiplexing to combine them into a single signal. The practice is sometimes called " multicasting".


ATSC television


United States

The ATSC digital television standard used in the
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
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 s ...
s to transmit one or more subchannels over a single digital signal. A virtual channel numbering scheme distinguishes broadcast subchannels by appending the television channel 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 network af ...
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 eight channels (in standard definition) and the Scripps Networks subchannel services Court TV, Ion Mystery, Bounce TV, Laff, Grit, Defy TV, and Scripps News. 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, officially the City and County of San Francisco, is a commercial, Financial District, San Francisco, financial, and Culture of San Francisco, cultural center of Northern California. With a population of 827,526 residents as of ...
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 in
Atlanta Atlanta ( ) is the List of capitals in the United States, capital and List of municipalities in Georgia (U.S. state), most populous city in the U.S. state of Georgia (U.S. state), Georgia. It is the county seat, seat of Fulton County, Georg ...
, Georgia, 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, 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 bro ...
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) 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 tuner An ATSC (Advanced Television Systems Committee) tuner, often called an ATSC receiver or HDTV tuner, is a type of television tuner that allows reception of digital television (DTV) television channels that use ATSC standards, as transmitted by tel ...
s will automatically add a new digital subchannel to their internal channel map, 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 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 government that regulates communications by radio, television, wire, internet, wi-fi, satellite, and cable across the United States. The FCC maintains j ...
(FCC) considers all subchannels carried by a single station to have the same call letters for legal 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 (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 17 August 2012, the CRTC gave approval to Leamington, Ontario 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, 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, 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 Telecommunications Commission), involving a fine of 4,453,150
Mexican peso The Mexican peso (Currency symbol, symbol: $; ISO 4217, currency code: MXN; also abbreviated Mex$ to distinguish it from peso, other peso-denominated currencies; referred to as the peso, Mexican peso, or colloquially varo) is the official curre ...
s. HiTV subchannels began broadcasting on an intermittent basis in 2013 and were almost completely deactivated in late 2014. Televisa 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 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 is not carried out in the interest of Profit (economics), profit. The opposite is Commerce, commercial, something that primarily serves profit interests and is focused on bu ...
networks SBS Television and ABC Television). 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, NITV and SBS WorldWatch) and a HD simulcast of its primary channel ( SBS HD); as well as its SBS Viceland and SBS World Movies channels with no SD simulcasts. * ABC Television offers three unique SD subchannels (
ABC TV Plus ABC Family is an Australian free-to-air television channel owned by the Australian Broadcasting Corporation and part of its ABC Television (Australian TV network), ABC Television network. The television channel, channel broadcasts a range of f ...
/ ABC Kids, ABC Me, and
ABC News ABC News most commonly refers to: * ABC News (Australia), a national news service of the Australian Broadcasting Corporation * ABC News (United States), a news-gathering and broadcasting division of the American Broadcasting Company ABC News may a ...
) and a HD simulcast of its primary channel ( ABC HD). * The Seven Network offers two unique SD subchannels ( 7two and 7flix), a datacasting channel ( Racing.com) and a HD version of its primary channel (
7HD Seven Network (stylised 7Network, and commonly known as Channel Seven or simply Seven) is an Australian commercial free-to-air Television broadcasting in Australia, television network. It is owned by Seven West Media, Seven West Media Limited, ...
) as well as its 7two, 7mate and 7Bravo channels, with no SD simulcasts for both 7mate and 7Bravo. * 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) as well as a HD simulcast of its 9Gem channel. * Network 10 offers two unique SD subchannels ( 10 Peach, and 10 Shake), two datacasting channels ( TVSN and
gecko Geckos are small, mostly carnivorous lizards that have a wide distribution, found on every continent except Antarctica. Belonging to the infraorder Gekkota, geckos are found in warm climates. They range from . Geckos are unique among lizards ...
) and a HD simulcast of its primary channel ( 10 HD) as well as their 10 Bold channel with no SD simulcast. Community television stations in
Melbourne Melbourne ( , ; Boonwurrung language, Boonwurrung/ or ) is the List of Australian capital cities, capital and List of cities in Australia by population, most populous city of the States and territories of Australia, Australian state of Victori ...
( C31) and
Adelaide Adelaide ( , ; ) is the list of Australian capital cities, capital and most populous city of South Australia, as well as the list of cities in Australia by population, fifth-most populous city in Australia. The name "Adelaide" may refer to ei ...
( 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 Conservatism is a cultural, social, and political philosophy and ideology that seeks to promote and preserve traditional institutions, customs, and values. The central tenets of conservatism may vary in relation to the culture and civiliza ...
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 continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
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 currently has four of its digital channels (
ITV1 ITV1 (formerly known as ITV) is a British free-to-air Public service broadcasting in the United Kingdom, public broadcast television channel owned and operated by the British media company ITV plc. It provides the ITV (TV network), Channel 3 ...
,
ITV2 ITV2 is a Television in the United Kingdom, 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 fiv ...
, ITV3 and ITV4) broadcasting on one multiplexed service, while two others ( ITV2 +1 and
CITV CITV is a British children's morning programming block on ITV2 and formerly a free-to-air channel owned by ITV plc. CITV, then Children's ITV, launched on 3 January 1983 as a late afternoon programming block on the ITV network for children aged ...
) are each broadcast on another, separate multiplex.


ISDB television

In
Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...
and
Latin America Latin America is the cultural region of the Americas where Romance languages are predominantly spoken, primarily Spanish language, Spanish and Portuguese language, Portuguese. Latin America is defined according to cultural identity, not geogr ...
(except
Colombia Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...
,
Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...
and
Panama Panama, officially the Republic of Panama, is a country in Latin America at the southern end of Central America, bordering South America. It is bordered by Costa Rica to the west, Colombia to the southeast, the Caribbean Sea to the north, and ...
), ISDB (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 Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
, 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 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 CBS Corporation was an American multinational media company with interests primarily in commercial broadcasting, publishing and television production. It was split from Viacom on December 31, 2005, alongside an entirely new Viacom; both ...
through its CBS Television Stations 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 network af ...
s of CBS and
The CW The CW Network, LLC (commonly referred to as The CW or simply CW) is an American commercial broadcast television network which is controlled by Nexstar Media Group through a 75% ownership interest. The network's name is derived from the firs ...
, 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 (NYC), is the most populous city in the United States, located at the southern tip of New York State on one of the world's largest natural harbors. The city comprises five boroughs, each coextensive w ...
and
Philadelphia Philadelphia ( ), colloquially referred to as Philly, is the List of municipalities in Pennsylvania, most populous city in the U.S. state of Pennsylvania and the List of United States cities by population, sixth-most populous city in the Unit ...
(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 located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
, 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 part ...
, France 2, Canal+, M6 and
Arte Arte (, , ; ' ('), sometimes stylised in lowercase or uppercase in its logo) is a European Union, European public service Television channel, channel dedicated to culture. It is made up of three separate companies: the Strasbourg-based Europea ...
; 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 Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...
, four HD services are currently transmitted over terrestrial frequencies: BBC One HD, BBC Two HD, ITV HD and Channel 4 HD ( S4C Clirlun 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 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 Local may refer to: Geography and transportation * Local (train), a train serving local traffic demand * Local, Missouri, a community in the United States Arts, entertainment, and media * ''Local'' (comics), a limited series comic book by Bria ...
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 Wheeling is a city in Ohio County, West Virginia, Ohio and Marshall County, West Virginia, Marshall counties in the U.S. state of West Virginia. The county seat of Ohio County, it lies along the Ohio River in the foothills of the Appalachian Mo ...
/ Steubenville, Ohio market, which for decades was home to only two stations (CBS affiliate WTRF-TV and NBC affiliate WTOV-TV; 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 Allegheny County, Pennsylvania, United States, and its county seat. It is the List of municipalities in Pennsylvania#Municipalities, second-most populous city in Pennsylvania (after Philadelphia) and the List of Un ...
(and to a lesser extent Columbus and
Youngstown, Ohio Youngstown is a city in Mahoning County, Ohio, United States, and its county seat. It is the List of municipalities in Ohio, 11th-most populous city in Ohio with a population of 60,068 at the 2020 United States census, 2020 census. The Mahoning ...
) 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 MyNetworkTV (stylized as mynetworkTV; unofficially abbreviated MNT or MNTV) is an American commercial broadcast television syndication service and former television network owned by Fox Corporation, operated by its Fox Television Stations ...
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, 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). 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 Estrella TV and Telemundo) 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 List of capitals in the United States, capital and List of municipalities in Indiana, most populous city of the U.S. state of Indiana and the county seat of Marion County, Indiana, Marion ...
,
Indiana Indiana ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Michigan to the northwest, Michigan to the north and northeast, Ohio to the east, the Ohio River and Kentucky to the 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 an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...
– which converted its 4.2 subchannel as an independent station in January 2015 as a result of owner Tribune Media selling the local rights to the CW affiliation that was to move from its main feed on 4.1 to Media General-owned WISH-TV, 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 peninsular U.S. state, state in the Great Lakes region, Great Lakes region of the Upper Midwest, Upper Midwestern United States. It shares water and land boundaries with Minnesota to the northwest, Wisconsin to the west, ...
and northern
Minnesota Minnesota ( ) is a U.S. state, state in the Upper Midwestern region of the United States. It is bordered by the Canadian provinces of Manitoba and Ontario to the north and east and by the U.S. states of Wisconsin to the east, Iowa to the so ...
, 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's virtual quadropoly in Duluth, 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 bro ...
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 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 List of capitals in the United States, capital city of the U.S. state of New York (state), New York. It is located on the west bank of the Hudson River, about south of its confluence with the Mohawk River. Albany is the oldes ...
. While WRGB broadcasts its main digital on VHF channel 6 in high definition, CW-affiliated sister station WCWN 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, but most have been due to companies who use sidecar companies to create virtual duopolies via local marketing agreements 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 station that own the non-licensed assets of other stations. Many companies such as Sinclair Broadcast Group (via Cunningham Broadcasting, Deerfield Media, & Howard Stirk Holdings),
Nexstar Media Group Nexstar Media Group, Inc. is an American publicly traded media company with headquarters in Irving, Texas, Midtown Manhattan, and Chicago. The company is the largest television station owner in the United States, owning 197 television station ...
(via Mission Broadcasting & Vaughan Media), and Gray Television (via American Spirit Media & SagamoreHill Broadcasting) 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 College athletics in the United States, student athletics among about 1,100 schools in the United States, and Simon Fraser University, 1 in Canada. ...
that took effect in 2011, which gave cable networks TBS, TNT and TruTV 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 and Chargers play at the same time, Fox is allowed to broadcast the second game on MyNetworkTV affiliate KCOP-TV, or CBS on independent KCAL-TV, depending on the game's carrier that specific week); all four of the major sports leagues (the NFL, the NBA,
Major League Baseball Major League Baseball (MLB) is a professional baseball league composed of 30 teams, divided equally between the National League (baseball), National League (NL) and the American League (AL), with 29 in the United States and 1 in Canada. MLB i ...
and the
NHL The National Hockey League (NHL; , ''LNH'') is a professional ice hockey league in North America composed of 32 teams25 in the United States and 7 in Canada. The NHL is one of the major professional sports leagues in the United States and Cana ...
) 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 Minor League Baseball (MiLB) is a professional baseball organization below Major League Baseball (MLB), constituted of teams affiliated with MLB clubs. It was founded on September 5, 1901, in response to the growing dominance of the National Le ...
,
American Hockey League The American Hockey League (AHL) is a professional ice hockey league in North America that serves as the primary developmental league of the National Hockey League (NHL). The league comprises 32 teams, with 26 in the United States and 6 in Cana ...
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 Retransmission consent is a provision of the 1992 United States Cable Television Consumer Protection and Competition Act that requires cable operators and other multichannel video programming distributors (MVPDs) to obtain permission from commerc ...
. Channels such as Sportsman Channel (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, for instance, carried
college football College football is gridiron football that is played by teams of amateur Student athlete, student-athletes at universities and colleges. It was through collegiate competition that gridiron football American football in the United States, firs ...
from historically black colleges and universities until 2013. In January 2016, Sinclair Broadcast Group 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 completely or partially surrounded by a tiered structure designed to allow spectators to stand or sit ...
in August 2017, following the formation of a multi-platform network venture with the Chicago White Sox's Silver Chalice unit and 120 Sports. 2023 saw the moves of two
National Hockey League The National Hockey League (NHL; , ''LNH'') is a professional ice hockey league in North America composed of 32 teams25 in the United States and 7 in Canada. The NHL is one of the major professional sports leagues in the United States and Cana ...
team broadcasts to digital subchannels, in at least part of the team's market. In May 2023, the
Vegas Golden Knights The Vegas Golden Knights are a professional ice hockey team based in the Las Vegas Valley, Las Vegas metropolitan area. The Golden Knights compete in the National Hockey League (NHL) as a member of the Pacific Division (NHL), Pacific Division ...
and Scripps Sports announced plans to bring the team's broadcasts to over-the-air television in the home market; as part of the deal, Golden Knights games air on the second subchannel of KIVI in Boise, KSAW-LD in Twin Falls, and the Montana Television Network. In October of that year, the
Arizona Coyotes The Arizona Coyotes are an inactive professional ice hockey team based in the Phoenix metropolitan area. They competed in the National Hockey League (NHL) as a member of the Central Division (NHL), Central Division (1996–1998, 2021–2024) and ...
moved their broadcasts to Scripps Sports, where the games air on the second subchannel of KNXV in Phoenix and KGUN in Tucson.


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 (a service exclusive to NBC stations that operated from 2004 to 2008), The AccuWeather Channel, WeatherNation TV (which also maintains limited exclusive distribution on pay television services) and TouchVision. Locally programmed news subchannels (such as News 9 Now / News on 6 Now on KWTV in
Oklahoma City Oklahoma City (), officially the City of Oklahoma City, and often shortened to OKC, is the List of capitals in the United States, capital and List of municipalities in Oklahoma, most populous city of the U.S. state of Oklahoma. The county seat ...
and KOTV in
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or NewsChannel 5+ on WTVF in
Nashville Nashville, often known as Music City, is the capital and List of municipalities in Tennessee, most populous city in the U.S. state of Tennessee. It is the county seat, seat of Davidson County, Tennessee, Davidson County in Middle Tennessee, locat ...
,
Tennessee Tennessee (, ), officially the State of Tennessee, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Kentucky to the north, Virginia to the northeast, North Carolina t ...
) 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 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

The first major nationally distributed general entertainment digital multicast television network, or diginet, for use on subchannels was Retro Television Network in 2005. Several new services launched or attempted to launch in 2008, including
This TV This TV (also known as This TV Network and alternately stylized as thisTV) was an American free-to-air television network owned by Allen Media Broadcast Networks, LLC, part of the Allen Media Group division of Entertainment Studios. Originally ...
, utilizing classic TV programming and library movies. This time period also saw the launch of some of the first services for public TV stations in the United States, such as Create. The field of diginets grew throughout the 2010s. MeTV, once a local service in Chicago and Milwaukee, became nationally distributed in 2010; by 2014, it was the most widely distributed diginet, and it remains the most watched with prime time viewership eclipsing some cable channels. Station groups also increased their presence in the space, most notably the E. W. Scripps Company's 2017 acquisition of Katz Broadcasting, which was seen as giving the sector legitimacy. Ratings and coverage have increased as these channels seek to reach cord cutters who still use antennas to receive broadcast signals. Diginets generally are reliant on national advertising revenue and, in some cases, pay stations to be carried on their subchannels, prizing lower channel numbers. Some have obtained national distribution on paid and free ad-supported streaming TV services.


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 The world is the totality of entities, the whole of reality, or everything that Existence, exists. The nature of the world has been conceptualized differently in different fields. Some conceptions see the world as unique, while others talk ...
, and Create. In the Washington, D.C. area, MHz Networks is available as ten subchannels transmitted by two stations, with their virtual channels mapped uniformly, making them appear as if they are transmitted by one station. In some U.S. states, statewide educational, cultural or 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 New York, also called New York State, is a state in the northeastern United States. Bordered by New England to the east, Canada to the north, and Pennsylvania and New Jersey to the south, its territory extends into both the Atlantic Ocean and ...
broadcaster ThinkBright TV). The use of subchannels has also allowed
educational television Educational television or learning television is the use of television programs in the field of distance education. It may be in the form of individual television programs or dedicated specialty channels that are often associated with cable televi ...
broadcasters to sell off former secondary PBS analogue stations to commercial broadcasters (such as WNEQ in Buffalo, which its sister station WNED-TV sold in 1999 to
LIN TV LIN Media was an American holding company founded in 1994 that operated 43 television stations. All except one were affiliates of the six major U.S. television networks. One of the remaining stations was a low-powered weather station in In ...
(now owned by
Nexstar Media Group Nexstar Media Group, Inc. is an American publicly traded media company with headquarters in Irving, Texas, Midtown Manhattan, and Chicago. The company is the largest television station owner in the United States, owning 197 television station ...
) to become 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 telecourses, which are recorded by instructors and students for later use, allowing the station's main channel to air a generalized
schedule A schedule (, ) or a timetable, as a basic time-management tool, consists of a list of times at which possible tasks, events, or actions are intended to take place, or of a sequence of events in the chronological order in which such thing ...
in the morning and overnight hours.


Temporary installations

Subchannels and transmitter reconfigurations have been used to temporarily restore service from a station that is unable to broadcast for technical, weather-related, or other reasons using the facilities of another. This use dates to the early days of digital television: in the immediate aftermath of the 11 September attacks, which destroyed the primary TV transmission site in New York City, WWOR-TV was broadcast as a subchannel of co-owned WNYW-DT. Competing stations in a market have even offered each other support; in 2009, Weigel Broadcasting offered the use of a subchannel to Milwaukee's WTMJ-TV when its transmitter was disabled by lightning, only for WTMJ to reciprocate the next year when flooding took Weigel's WDJT-TV out of service for three days. For five months from October 2019 to 2020, commonly operated WBBH-TV and WZVN-TV in Fort Myers, broadcast from the former's facility on one multiplex to allow for an overhaul of the latter's antenna.


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 commonly owned broadcast
radio station Radio broadcasting is the broadcasting of audio (sound), sometimes with related metadata, by radio waves to radio receivers belonging to a public audience. In terrestrial radio broadcasting the radio waves are broadcast by a land-based rad ...
is simulcast over a subchannel (for instance, KPJK in
San Mateo, California San Mateo ( ) is the most populous city in San Mateo County, California, United States, on the San Francisco Peninsula. It is part of the San Francisco Bay Area metropolitan region, and is located about south of San Francisco. San Mateo border ...
broadcasts former FM sister KCSM on its DT3 signal). WANN-CD in
Atlanta Atlanta ( ) is the List of capitals in the United States, capital and List of municipalities in Georgia (U.S. state), most populous city in the U.S. state of Georgia (U.S. state), Georgia. It is the county seat, seat of Fulton County, Georg ...
offers six radio stations owned by
iHeartMedia iHeartMedia, Inc., or CC Media Holdings, Inc., is an American mass media corporation headquartered in San Antonio, Texas. It is the holding company of iHeartCommunications, Inc., formerly Clear Channel Communications, Inc., a company founded by ...
, in addition to ten television channels. Non-broadcast content, subscription television channels or datacasting 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
pay television Pay television, also known as subscription television, premium television or, when referring to an individual service, a premium channel, refers to Subscription business model, subscription-based television services, usually provided by multichan ...
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 A bitstream (or bit stream), also known as binary sequence, is a sequence of bits. A bytestream is a sequence of bytes. Typically, each byte is an 8-bit quantity, and so the term octet stream is sometimes used interchangeably. An octet may ...
is divided. Therefore, station managers and 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 VBR encoding, more subchannels can be combined. 1×720p + 3×480i is becoming more common. For a
frame rate Frame rate, most commonly expressed in frame/s, or FPS, is typically the frequency (rate) at which consecutive images (Film frame, frames) are captured or displayed. This definition applies to film and video cameras, computer animation, and moti ...
of 30 p or 60 i, uncompressed DTV channels have the following data rates in
megapixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a Raster graphics, raster image, or the smallest addressable element in a dot matrix display device. In most digital display devices, p ...
s per second: For ATSC, these must be compressed into 19.4 Mbit/s total per physical 6 MHz RF channel over the air, and 38.8 Mbit/s for cable.


Digital radio

Various forms of digital radio also allow for multiple program streams.


HD Radio

The primary distinguishing feature of HD Radio has been its ability to multiplex an
FM radio FM broadcasting is a method of radio broadcasting that uses frequency modulation (FM) of the radio broadcast carrier wave. Invented in 1933 by American engineer Edwin Armstrong, wide-band FM is used worldwide to transmit high fidelity, high-f ...
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 A legal fiction is a construct used in the law where a thing is taken to be true, which is not in fact true, in order to achieve an outcome. Legal fictions can be employed by the courts or found in legislation. Legal fictions are different from ...
. Since HD Radio was introduced in the United States in the late 2000s (decade), the FCC has allowed American broadcasters to use low-powered 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 A media market, broadcast market, media region, designated market area (DMA), television market area, or simply market is a region where the population can receive the same (or similar) television station, television and radio broadcasting, ra ...
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 Adjacent-channel interference (ACI) is interference caused by extraneous power from a signal in an adjacent channel. ACI may be caused by inadequate filtering (such as incomplete filtering of unwanted modulation products in FM systems), improp ...
caused by the greater bandwidth it requires, with little benefit. WWFD has operated as a digital-only station with no analog signal under 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(.)" 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 stations * DAB and DVB, international digital radio-television standards in use in
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
,
Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
and
New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...
* QAM tuner


References


External links

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