In broadcasting,digital subchannels are a method of transmitting more than one independent program stream simultaneously from the samedigital radio ortelevisionstation on the sameradio frequency channel. This is done by usingdata compression techniques to reduce the size of each individual program stream, andmultiplexing to combine them into a single signal. The practice is sometimes called "multicasting".

TheATSC digital television standard used in theUnited States supports multiple program streams over-the-air, allowingtelevision stations to transmit one or more subchannels over a single digital signal. Avirtual channel numbering scheme distinguishes broadcast subchannels by appending thetelevision 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 foranalog channels. For example, most of theowned-and-operated stations/affiliates ofTrinity 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 (instandard definition) and theScripps Networks subchannel servicesCourt TV,Ion Mystery,Bounce TV,Laff,Grit,Defy TV, andScripps News. More programming streams can be fit into a single channel space at the cost of broadcast quality. Among smaller stations,KAXT-CD inSan Francisco 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 inAtlanta, Georgia, with ten video and ten audio feeds, comes at a close second. Several cable-to-air^{[clarification needed]} broadcasters, such as those inWillmar, Minnesota andCortez, Colorado, have multiplexed more than five separatecable television channels into subchannels of one signal.

Operating in a sector traditionally lacking subchannels,digital cable television providerMusic Choice packages its nearly 50 music channels (includingMusic 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.^{[citation needed]}

MostATSC tuners will automatically add a new digital subchannel to their internalchannel 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 theATSC-M/H standard.

TheFederal Communications Commission (FCC) considers all subchannels carried by a single station to have the samecall letters for legalidentification purposes. However, within the broadcast sales industry, to differentiate subchannels, the initial letter of a call sign changes per subchannel.As perNielsen, digital stations identified with a "W" call letter will generally have their subchannels identified with an "E" (.2), "G" (.3), "H" (.4), "I" (.5) or "J" (.6). Digital stations identified with a "K" call-letter will generally have their subchannels identified with an "N" (.2), "O" (.3), "Q" (.4), "R" (.5) or "S" (.6). For example, if the call letters are WFRC and the station broadcasts on channel 10, then the 10.2 subchannel is identified as EFRC, 10.3 is GFRC, 10.4 is HFRC, 10.5 is IFRC and 10.6 is JFRC. If the call letters are KFRC and the station broadcasts on channel 10, then 10.2 is identified as NFRC, 10.3 is OFRC, 10.4 is QFRC, 10.5 is RFRC and 10.6 is SFRC.^{[citation needed]}

Although digital television services in Canada use the same ATSC technology as the United States, none of thestations 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, theCanadian 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 toLeamington, Ontario community stationCFTV-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.^[1]

Some Mexican TV stations use digital subchannels as they are used in the United States. TheSistema Público de Radiodifusión del Estado Mexicano, a public broadcaster, operates 26 multiplexed transmitters throughout Mexico carrying five to six public television services, whileXHTRES-TDT carries Imagen Radio audio on a subchannel.^{[citation needed]}

One notable experiment involving digital subchannels in Mexico was undertaken byTV Azteca, which used its three muxes in the Mexico City area to broadcast a service called Hi-TV, featuring several channels encoded inH.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 atCOFETEL (the Federal Telecommunications Commission), involving a fine of 4,453,150Mexican pesos. HiTV subchannels began broadcasting on an intermittent basis in 2013 and were almost completely deactivated in late 2014.^{[citation needed]}

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+ andadn40.^{[citation needed]}

In October 2016, theIFT 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.^{[citation needed]}

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.^{[citation needed]}

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 ofnon-commercial networksSBS Television andABC 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 andSBS WorldWatch) and a HD simulcast of its primary channel (SBS HD); as well as itsSBS Viceland andSBS World Movies channels with no SD simulcasts.
• ABC Television offers three unique SD subchannels (ABC TV Plus/ABC Kids,ABC Me, andABC News) and a HD simulcast of its primary channel (ABC HD).
• The Seven Network offers two unique SD subchannels (7two and7flix), adatacasting channel (Racing.com) and a HD version of its primary channel (7HD) as well as its 7two,7mate and7Bravo channels, with no SD simulcasts for both 7mate and 7Bravo.
• The Nine Network offers four unique SD subchannels (9Go!,9Rush,9Gem and9Life), 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, and10 Shake), two datacasting channels (TVSN andgecko) and a HD simulcast of its primary channel (10 HD) as well as their10 Bold channel with no SD simulcast.

Community television stations inMelbourne (C31) andAdelaide (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 andFly TV – closed after less than two years in operation in 2003 as a reaction to budget cuts by theconservativeHoward government underCommunications MinisterAlston 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.

As most digital services inEurope 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,ITV2,ITV3 andITV4) broadcasting on one multiplexed service, while two others (ITV2 +1 andCITV) are each broadcast on another, separate multiplex.

InJapan andLatin America (exceptColombia,Mexico andPanama),ISDB (similar to the DVB format) is used, and was specifically designed with physicalRF segments that could be split to use for different subchannels. InBrazil, a digital subchannel was only allowed to the public and educational stations,^[2][3] until 2024, when commercial TV networks were allowed to have subchannels.^[4]

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 transmithigh 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.^{[citation needed]} Because of the tradeoffs, stations owned byCBS Corporation through itsCBS Television Stations subsidiary (which includeowned-and-operated stations ofCBS andThe CW, and someindependent 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 inNew York City andPhiladelphia (the company later announced the creation ofDecades, a multicast network part-owned by CBS which aired on all CBS and CW owned-and-operated stations from 2015 to 2018).^[5]

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.^{[citation needed]} For example, inFrance, there are only five HD services: one each forTF1,France 2,Canal+,M6 andArte; in theUnited Kingdom, four HD services are currently transmitted over terrestrial frequencies:BBC One HD,BBC Two HD,ITV HD andChannel 4 HD (S4C Clirlun is broadcast in Wales instead of Channel 4 HD).^[8]

The examples and perspective in this sectiondeal primarily with the United States and do not represent aworldwide view of the subject. You mayimprove this section, discuss the issue on thetalk page, or create a new section, as appropriate.(February 2015) (Learn how and when to remove this message)

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 smallermarkets 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 ownlocal andsyndicated programming commitments, and overlapping network programs that would be tough to schedule outside of regular timeslots. A prime example is theWheeling, West Virginia/Steubenville, Ohio market, which for decades was home to only two stations (CBS affiliateWTRF-TV and NBC affiliateWTOV-TV; the cable-onlyWBWO also served the market as aWB and now as a CW affiliate) and had to mostly rely on stations inPittsburgh (and to a lesser extentColumbus andYoungstown, 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).^[7]

Upon their launches in September 2006, The CW andMyNetworkTV 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 predecessorThe 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 asEstrella TV andTelemundo) 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 asWTTV inIndianapolis,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 WTTVsatellite – which converted its 4.2 subchannel as an independent station in January 2015 as a result of ownerTribune Media selling the local rights to the CW affiliation that was to move from its main feed on 4.1 toMedia General-ownedWISH-TV, whose CBS affiliation was assumed by WTTV).^[9][10]

Digital subchannels are also used to relay stations beyond their traditional signal coverage areas to reach an entire market. In theUpper Peninsula ofMichigan and northernMinnesota, 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 ofduopolies, where transmitters scattered through a large geographical area allow multiple networks and channels to be carried. The most prominent example is theGranite Broadcasting Corporation'svirtual quadropoly inDuluth, Minnesota, which consists of two separate full-power stations, NBC affiliateKBJR-TV and CBS affiliateKDLH, 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 onsatellite stationKRII inChisholm, providing theIron Range region (located north of Duluth) programming from networks that were previously unavailable over-the-air. In theTraverse City-Cheboygan market in Upper Michigan, NBC affiliateWPBN/WTOM also simulcasts sister stationWGTU/WGTQ, providing that station's ABC programming to the entire market; CBS affiliateWWTV/WWUP carries its Fox-affiliated sisterWFQX/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 orClass A station or by acable television 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 lowVHF 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 affiliateWHBF-TV inRock Island, Illinois. While WHBF broadcasts its main digital on VHF channel 4 in high definition, CW-affiliatedsister stationKGCW inBurlington, Iowa, relays a standard-definition subchannel feed of WHBF over virtual channel 26.4.

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 the2016 United States wireless spectrum auction, but most have been due to companies who use sidecar companies to create virtualduopolies vialocal 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 asSinclair Broadcast Group (viaCunningham Broadcasting,Deerfield Media, &Howard Stirk Holdings),Nexstar Media Group (viaMission Broadcasting &Vaughan Media), andGray Television (viaAmerican Spirit Media &SagamoreHill Broadcasting) have been doing this, partially due to regulation pressure.

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 theNCAA men's basketball tournament in addition to those broadcast on the main digital channel (this was superseded as a result ofa new television agreement with theNCAA that took effect in 2011, which gave cable networksTBS,TNT andTruTV partial rights to the tournament). Most of themajor 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 theRams andChargers play at the same time, Fox is allowed to broadcast the second game on MyNetworkTV affiliateKCOP-TV, or CBS on independentKCAL-TV, depending on the game's carrier that specific week); all four of the major sports leagues (theNFL, theNBA,Major League Baseball and theNHL) haveout-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, thoughminor 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 throughretransmission consent. Channels such asSportsman Channel (and the now-defunctUniversal 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, carriedcollege football fromhistorically black colleges and universities until 2013.

In January 2016,Sinclair Broadcast Group launched a 24-hour feed of itsAmerican Sports Network sports syndication service on subchannels of ten stations owned and/or operated by the group; the ASN multicast network was subsequently replaced byStadium in August 2017, following the formation of a multi-platform network venture with theChicago White Sox's Silver Chalice unit and120 Sports.

2023 saw the moves of twoNational Hockey League team broadcasts to digital subchannels, in at least part of the team's market. In May 2023, theVegas Golden Knights andScripps 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 ofKIVI inBoise,KSAW-LD inTwin Falls, and theMontana Television Network.^[11] In October of that year, theArizona Coyotes moved their broadcasts to Scripps Sports, where the games air on the second subchannel ofKNXV inPhoenix andKGUN inTucson.^[12]

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) andTouchVision. Locally programmed news subchannels (such asNews 9 Now / News on 6 Now onKWTV inOklahoma City andKOTV inTulsa, Oklahoma or NewsChannel 5+ onWTVF inNashville,Tennessee) often carry rebroadcasts and simulcasts of local news programs seen on the station's main feed, in some cases displaying aticker 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 significantbreaking 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.

The first major nationally distributed general entertainmentdigital multicast television network, or diginet, for use on subchannels wasRetro Television Network in 2005. Several new services launched or attempted to launch in 2008, includingThis TV, 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 asCreate.

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 theE. 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 reachcord 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.

ManyPBS 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, andCreate. In theWashington, D.C. area,MHz Networks is available as ten subchannels transmitted by two stations, with theirvirtual channels mapped uniformly, making them appear as if they are transmitted by one station.

In some U.S. states, statewide educational, cultural orpublic affairs services are carried on a digital subchannel of a PBS member station or network (such as theMinnesota Channel,PBS Wisconsin's Wisconsin Channel, orNew York State broadcasterThinkBright TV). The use of subchannels has also allowededucational television broadcasters to sell off former secondary PBS analogue stations tocommercial broadcasters (such as WNEQ inBuffalo, which its sister stationWNED-TV sold in 1999 toLIN TV (now owned byNexstar Media Group) to becomeWNLO, 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 totelecourses, which are recorded by instructors and students for later use, allowing the station's main channel to air a generalizedschedule in the morning andovernight hours.

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-ownedWNYW-DT.^[13] Competing stations in a market have even offered each other support; in 2009,Weigel Broadcasting offered the use of a subchannel to Milwaukee'sWTMJ-TV when its transmitter was disabled by lightning, only for WTMJ to reciprocate the next year when flooding took Weigel'sWDJT-TV out of service for three days.^[14][15] For five months from October 2019 to 2020, commonly operatedWBBH-TV andWZVN-TV inFort Myers, broadcast from the former's facility on one multiplex to allow for an overhaul of the latter's antenna.^[16]

In rare cases, digital television broadcasters have included a service known asDTV radio, in which the audio of acommonly owned broadcastradio station is simulcast over a subchannel (for instance,KPJK inSan Mateo, California broadcasts former FM sisterKCSM on its DT3 signal).WANN-CD inAtlanta offers six radio stations owned byiHeartMedia, in addition to ten television channels.

Non-broadcast content,subscription television channels ordatacasting 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-airpay television service that usedH.264 compression instead of standardMPEG-2. Mobile DTV now usesMPEG-4 compression, which like H.264 yields a much lowerbitrate for the samevideo 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 freedigital video recorder (DVR) service allowing recordings of local broadcast channels and free and subscription internet content.

The examples and perspective in this sectiondeal primarily with ATSC and do not represent aworldwide view of the subject. You mayimprove this section, discuss the issue on thetalk page, or create a new section, as appropriate.(June 2023) (Learn how and when to remove this message)

Digital television supports multiple digital subchannels if the 19.39 Mbit/s (megabits per second)bitstream is divided. Therefore, station managers andbroadcast 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 ofvariable bitrate encoding):

With improvements in MPEG encoding, and tighterVBR encoding, more subchannels can be combined. 1×720p + 3×480i is becoming more common.^[when?]

For aframe rate of 30p or 60i, uncompressed DTV channels have the followingdata rates inmegapixels per second:

ForATSC, these must be compressed into 19.4 Mbit/s total per physical 6 MHzRF channel over the air, and 38.8 Mbit/s for cable.

Various forms ofdigital radio also allow for multiple program streams.

The primary distinguishing feature ofHD Radio has been its ability to multiplex anFM 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 beingin-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 alegal fiction. Since HD Radio was introduced in the United States in the late 2000s (decade), the FCC has allowed American broadcasters to use low-poweredtranslators to transmit HD Radio subchannels in analog FM. This has allowed broadcasters to increase the number of programming choices available in a givenmedia market beyond FCC limits.

AM broadcasting generally lacks the bandwidth to multiplex; though in theory an AM station could transmit two separate channels usingC-QUAMAM stereo, there is a limit to how far the two audio channels can be separated, and thuscrosstalk 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 increasedadjacent-channel interference caused by the greater bandwidth it requires, with little benefit.^[17]WWFD has operated as a digital-only station with no analog signal underspecial 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.^[18] 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(.)"^[19] A proposed FCC rule would require stations that wish to multiplex their digital AM signals to request and receive permission to do so.^[19]

This sectionneeds expansion. You can help byadding to it.(April 2010)

• In-band on-channel (IBOC), digital radio technology allowing digital subchannels onFM stations
• DAB andDVB, international digital radio-television standards in use inEurope,Australia andNew Zealand
• QAM tuner

• "How Digital Television Works".HowStuffWorks. 10 January 2001. Retrieved29 January 2007.

• ATSC
• Digital television
• High-definition television
• Television technology

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