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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 systems ...
or
television Television (TV), sometimes shortened to tele or telly, is a telecommunication medium used for transmitting moving images in monochrome (black and white), or in color, and in two or three dimensions and sound. The term can refer to a televisi ...
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 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 upper ...
channel. This is done by using
data compression In signal processing, 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 compression re ...
techniques to reduce the size of each individual program stream, and
multiplexing In telecommunications and computer networks, 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. For ex ...
to combine them into a single signal. The practice is sometimes called "
multicasting 250px 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 w ...
".


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 s ...
digital television standard used in the
United States The United States of America (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 self-governing territories, 326 India ...
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 r ...
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 c ...
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, w ...
s/
affiliates In the broadcasting industry (particularly in North America), a network affiliate or affiliated station is a local broadcaster, owned by a company other than the owner of the network, which carries some or all of the lineup of television programs ...
of
Trinity Broadcasting Network The Trinity Broadcasting Network (TBN) is an international Christian-based broadcast television network and the world's largest religious television network. TBN was headquartered in Costa Mesa, California until March 3, 2017 when it sold its hig ...
transmit five streams in the following format: The most of any large broadcaster in the United States,
Ion Television Ion is an American free-to-air television network/syndication service owned by the E. W. Scripps Company through the network's parent company, Ion Media. The network first began broadcasting on August 31, 1998 as Pax TV, focusing primarily on f ...
stations transmit six channels (in
standard definition Standard-definition television (SDTV, SD, often shortened to standard definition) is a television system which uses a resolution that is not considered to be either high or enhanced definition. SDTV and high-definition television (HDTV) are th ...
) and the
Katz Broadcasting Katz Broadcasting, LLC, doing business as Katz Networks, is an American specialized digital multicasting network media company and a subsidiary of E. W. Scripps Company. The company owns (as of 2019) five television networks that each carry program ...
subchannel services
Court TV Court TV is a digital broadcast network and former American cable television channel. It was originally launched in 1991 with a focus on crime-themed programs such as true crime documentary series, legal dramas, and coverage of prominent criminal ...
,
Court TV Mystery Court TV Mystery (formerly Escape, stylized as ESCAPE) is an American free-to-air television network owned by the Katz Broadcasting subsidiary of the E. W. Scripps Company. It focuses primarily on mystery and crime programming. It is available i ...
,
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 featu ...
, Laff, and Grit. 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 (/ˌsæn fɹənˈsɪskoʊ/; Spanish for "Saint Francis"), officially the City and County of San Francisco, is a cultural, commercial, and financial center in Northern California. San Francisco is the 16th most populous city in ...
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, United States. Digital television Digital channels The station's digital channel is multiplexed: References Exte ...
in
Atlanta, Georgia Atlanta () is the capital and most populous city of the U.S. state of Georgia. With an estimated 2019 population of 506,811, it is also the 37th most populous city in the United States. The city serves as the cultural and economic center of ...
, with ten video and six audio feeds, comes at a close second. Several cable-to-air broadcasters, such as those in
Willmar, Minnesota Willmar is a city in, and the county seat of, Kandiyohi County, Minnesota, United States. The population was 19,610 at the 2010 census. Willmar has been assigned ZIP code 56201 by the United States Postal Service. U.S. Highways 12 and 71 and M ...
and
Cortez, Colorado The City of 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 8,482 at the 2010 United States Census. History In 1886, the town w ...
, 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 broadcas ...
channels into subchannels of one signal. Operating in a sector traditionally lacking subchannels,
digital cable television Digital cable is the distribution of cable television using digital video compression for distribution. The technology was developed by General Instrument, which was succeeded by Motorola and subsequently by ARRIS Group. Cable companies converte ...
provider
Music Choice 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 households ...
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 400px, Multiple MPEG programs are combined then sent to a transmitting antenna. In the US broadcast digital TV system, an ATSC receiver then decodes the TS and displays it on a TV. An ATSC (Advanced Television Systems Committee) tuner, often called a ...
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 DMB in South Korea 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 ...
is also carried on ATSC stations, but as a separate service, according to the
ATSC-M/H ATSC-M/H (''Advanced Television Systems Committee - Mobile/Handheld'') is a U.S. standard for mobile digital TV that allows TV broadcasts to be received by mobile devices.Federal Communications Commission The Federal Communications Commission (FCC) is an independent agency of the United States government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdiction over the ...
(FCC) considers all subchannels carried by a single station to have the same
call letter Call or Calls may refer to: Arts, entertainment, and media Games * Call, a type of betting in poker * Call, in the game of contract bridge, a bid, pass, double, or redouble in the bidding stage Music and dance * Call (band), from Lahore, Pakist ...
s for legal
identification Identification or identify may refer to: Art and entertainment *''Identify'' (album) by Got7 *''Kill Command'', 2016 film, also known as ''Identify'' *"Identify" (song) *Identification (album), by Benjamin Ingrosso Business *Identity verificati ...
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 broadcasting ...
(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 is third-largest municipality in the Windsor-Essex County area (after the city of Windsor and town of LaSalle). It include ...
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 in t ...
, 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 and Imagen Televisión, as well as some local operators ...
, 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 (symbol: $; code: MXN) is the currency of Mexico. Modern peso and dollar currencies have a common origin in the 15th–19th century Spanish dollar, most continuing to use its sign, "$". The Mexican peso is the 15th most traded cur ...
s. HiTV subchannels began broadcasting on an intermittent basis in 2013 and were almost completely deactivated in late 2014.
Televisa Grupo Televisa, S.A.B. () 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. Much of its programming airs in the United States ...

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+ A, or a, is the first letter and the first vowel letter of the modern English alphabet and the ISO basic Latin alphabet. Its name in English is ''a'' (pronounced ), plural ''aes''. It is similar in shape to the Ancient Greek letter alpha, fro ...
and
adn40 XHTVM-TDT (virtual channel 40) is a television station in Mexico City, owned by Televisora del Valle de México and operated by TV Azteca. It is branded as ''adn40'' and available over the air in much of Mexico on TV Azteca's transmitters. Progra ...
. 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 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 The Special Broadcasting Service (SBS) is a hybrid-funded Australian public service broadcaster. About 80 per cent of funding for the company is derived from the Australian Government. SBS operates five TV channels (SBS, SBS Viceland, SBS World ...
and
ABC Television ABC Television is the national television network of the Australian Broadcasting Corporation launched in 1956. As a public broadcaster, the ABC provides four non-commercial channels within Australia, and ABC Australia, an advertiser-suppor ...
). Due to technical reasons, each network is currently only permitted one HD sub channel. All networks use their HD subchannel to provide a simulcast of their primary channel. Inclusive of their primary standard definition channels (ignoring HD): * SBS Television offers four unique SD subchannels (
SBS Viceland SBS Viceland (stylised as SBS VICELAND) is an Australian free-to-air television channel owned by the Special Broadcasting Service (SBS). It began as SBS TWO on 1 June 2009, and was branded as SBS 2 between 2013 and 2016. On 8 April 2017, SBS Vi ...
,
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 launch ...
,
SBS World Movies SBS World Movies is an Australian free-to-air television channel showing international movies. The channel features foreign language films, documentaries, independent and mainstream cinema and interviews with international movie stars. It was pr ...
, and
NITV National Indigenous Television (NITV) is an Australian free-to-air television channel that broadcasts programming produced and presented largely by Aboriginal and Torres Strait Islander people. It includes the half-hourly nightly ''NITV News'', ...
) 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 7.9% audience share. History Origins SBS began test ...
); as well as a HD simulcast of its Viceland channel. * ABC Television offers three unique SD subchannels (
ABC Comedy ABC TV Plus is an Australian free-to-air television channel owned by the Australian Broadcasting Corporation. The channel broadcasts a range of general entertainment programming. Between the hours of 5am and 7.30pm daily the channel's bandwidth i ...
/ABC Kids (Australia), ABC Kids, ABC Me, and ABC News (TV channel), ABC News) and a HD simulcast of its primary channel (ABC HD (Australian TV channel), ABC HD). * The Seven Network offers three unique SD subchannels (7TWO, 7mate and 7flix), a datacasting channel (Racing.com) and a HD simulcast of its primary channel (7HD) * The Nine Network offers three unique SD subchannels (9Go!, 9Rush, 9Gem and 9Life), a datacasting channel (Extra (Australian TV channel), Extra) and a HD simulcast of its primary channel (9HD); * Network Ten offers three unique SD subchannels (10 Bold, 10 Peach, and 10 Shake), two datacasting channels (TVSN and Spree TV) and a HD simulcast of its primary channel (Ten HD). Community television stations in Melbourne (C31 Melbourne, C31) and Adelaide (44 Adelaide) 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 channel, ABC Kids and Fly TV – closed after less than two years in operation in 2003 as a reaction to budget cuts by the Liberal Party of Australia, conservative Howard Government under Minister for Communications (Australia), Communications Minister Richard Alston (politician), 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 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 (TV network), ITV currently has four of its digital channels (ITV (TV channel), ITV, ITV2, ITV3 and ITV4) broadcasting on one multiplexed service, while two others (ITV2, ITV2 +1 and CITV) are each broadcast on another, separate multiplex.


ISDB television

In Japan and Brazil, ISDB (similar to the DVB format) is used, and was specifically designed with physical Radio frequency, 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 television, 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 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 affiliate, w ...
s of CBS and The CW, and some Independent station (North America), 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 WCBS-TV, New York City and KYW-TV, Philadelphia (the company later announced the creation of Decades (TV network), Decades, a multicast network part-owned by CBS which aired on all CBS-owned 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 Télévision Numérique Terrestre, France, there are only five HD services: one each for TF1, France 2, Canal+, M6 (television channel), M6 and Arte; in the Freeview (UK), United Kingdom, 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 media market, 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 programming, local and broadcast syndication, 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; the cable-only The CW Plus, WBWO also served the market as a The WB, WB and now as a CW affiliate) and had to mostly rely on stations in Pittsburgh (and to a lesser extent Columbus, Ohio, Columbus and Youngstown, Ohio) 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, 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 MundoFox, Estrella TV and Mexicanal) 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, Indiana – 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 Broadcast relay station#Satellite stations, satellite – 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 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 and northern Minnesota, 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 Duopoly (broadcasting), 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 Northland's NewsCenter, 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 broadcast relay station#satellite station, satellite station KRII in Chisholm, Minnesota, Chisholm, providing the Iron Range region (located north of Duluth) programming from networks that were previously unavailable over-the-air. In the Traverse City, Michigan, Traverse City-Cheboygan, Michigan, Cheboygan market in Upper Michigan, NBC affiliate WPBN-TV, WPBN/WTOM also simulcasts sister station WGTU, WGTU/WGTQ, providing that station's ABC programming to the entire market; CBS affiliate WWTV, WWTV/WWUP carries its Fox-affiliated sister WFQX-TV, 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 television service, 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 broadcas ...
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 Very high frequency, 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. 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.


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 Division I Basketball Championship, NCAA Men's Basketball Tournament in addition to those broadcast on the main digital channel (this was superseded as a result of NCAA March Madness (CBS/Turner), a new television agreement with the National Collegiate Athletics Association, NCAA that took effect in 2011, which gave cable networks TBS (TV network), TBS, TNT (U.S. TV network), 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 Los Angeles Rams, Rams and Los Angeles Chargers, 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 National Football League, NFL, the National Basketball Association, NBA, Major League Baseball and the National Hockey League, NHL) 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 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 (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 featu ...
, for instance, carried college football 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 (sports network), Stadium in August 2017, following the formation of a multi-platform network venture with the Chicago White Sox#Silver Chalice subsidiary, 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 (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-DT, KWTV in Oklahoma City and KOTV-DT, KOTV in Tulsa, Oklahoma or NewsChannel 5+ on WTVF in Nashville, Tennessee) often carry rebroadcasts and simulcasts of local news programs seen on the station's main feed, in some cases displaying a news ticker, 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

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, the Retro Television Network, 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 featu ...
, the female-targeted Escape (TV network), Escape and the male-targeted Grit) feature programming aimed at specific demographics. With few exceptions (such as Bounce TV and the now-defunct Live Well Network), 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 K38IZ-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, Heartland (TV network), Heartland, Tr3s and TheCoolTV), 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 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 five major networks or 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 cable & 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 r ...
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 Media General) 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 r ...
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 (now a MundoFox affiliate, since sold to the Mueriello 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, United States. Digital television Digital channels The station's digital channel is multiplexed: References Exte ...
in Atlanta, Georgia, Atlanta offers six radio stations owned by iHeartMedia, in addition to ten television channels. Non-broadcast content, pay television, 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 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 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 s ...
, these must be compressed into 19.4Mbit/s total per physical 6 MHz Radio frequency, 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 systems ...
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, Australia and New Zealand * QAM tuner


References

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