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HD Radio logo.

HD Radio ( HDR ) [1] es un término de marca registrada para la tecnología de radio digital en banda en el canal (IBOC) utilizada por las estaciones de radio AM y FM principalmente en los Estados Unidos, Canadá y México, con algunas implementaciones fuera de América del Norte. . El sistema transmite datos digitales adicionales asociados con las señales analógicas estándar de una estación de radio existente. , retransmitiendo la misma señal en formato digital con menos ruido. Los datos digitales también pueden incluir hasta tres señales de radio digitales adicionales, que pueden usarse para transmitir otras estaciones dentro de la misma asignación de frecuencia.

iBiquity desarrolló HD Radio, y el sistema fue seleccionado por la Comisión Federal de Comunicaciones (FCC) de EE. UU . en 2002 como método de transmisión de audio digital para los Estados Unidos, [2] [3] Se conoce oficialmente como NRSC-5 , con la última siendo la versión NRSC-5-D . [4] iBiquity fue adquirido por DTS en septiembre de 2015, llevando la tecnología HD Radio bajo el mismo nombre que los sistemas de sonido envolvente de cine del mismo nombre de DTS. [5] La tecnología y las marcas registradas de HD Radio fueron posteriormente adquiridas por Xperi en 2016.

HD Radio es uno de varios estándares de radio digital que generalmente son incompatibles entre sí. En Europa, Digital Audio Broadcasting (DAB, también conocido como Eureka 147) es el estándar más común, con Digital Radio Mondiale (configuraciones DRM30 y DRM +) diseñado principalmente para aplicaciones de onda corta y Compatible AM-Digital (CAM-D) para radio AM. FMeXtra era un estándar estadounidense de la competencia, pero este estándar se actualizó poco y desde entonces ha quedado inactivo.

HD Radio permite un modo totalmente digital. Dos estaciones AM lo usan, una bajo autorización experimental, la otra bajo las nuevas reglas adoptadas por la FCC en octubre de 2020. Todas las demás estaciones de radio AM y FM que usan HD Radio transmiten simultáneamente audio digital y analógico en la misma frecuencia (una digital híbrida- señal analógica), así como para agregar nuevos subcanales e información de texto. El contenido de las transmisiones de HD Radio es actualmente gratuito ; los oyentes deben comprar nuevos receptores para recibir la parte digital de la señal.

En mayo de 2018, se afirmó que la tecnología HD Radio era utilizada por más de 3500 servicios individuales, principalmente en los Estados Unidos. [6] Esto se compara con más de 2200 servicios que operan con el sistema DAB.

HD Radio aumenta el ancho de banda requerido en la banda FM a 400 kHz para la versión híbrida analógica / digital. Esto hace que la adopción fuera de los Estados Unidos sea problemática. En los Estados Unidos, los canales de la banda de transmisión de FM tienen un espaciado de 200 kHz, a diferencia de los 100 kHz que son normales en otros lugares. El espaciamiento de 200 kHz significa que, en la práctica, las estaciones que tienen áreas de cobertura concurrentes o adyacentes no estarán espaciadas a menos de 400 kHz para respetar las relaciones de protección que no se cumplirían con un espaciado de 200 kHz. [7] Esto también deja espacio para las bandas laterales digitales. Fuera de EE. UU., El espaciado puede ser de 300 kHz, lo que causa problemas con las bandas laterales digitales.

La FCC no ha indicado ninguna intención de interrumpir las transmisiones de radio analógicas como lo hizo con las transmisiones de televisión analógica , [2] porque no daría lugar a la recuperación de ningún derecho de espectro de radio que pudiera venderse. Por lo tanto, no existe una fecha límite en la que los consumidores deban comprar un receptor de HD Radio. Además, hay muchos más receptores de radio AM / FM analógicos que televisores analógicos que dependían de señales por aire, y muchos de ellos son receptores de automóviles o unidades portátiles que no se pueden actualizar.

Resumen [ editar ]

La información digital se transmite mediante OFDM con un formato de compresión de audio llamado HDC ( codificación de alta definición ). HDC es un códec patentado basado en el estándar HE-AAC de MPEG-4 , pero incompatible con él . [8] Utiliza un algoritmo de compresión de datos de audio de transformada de coseno discreta modificada (MDCT) . [9]

Las estaciones equipadas con HD Radio pagan una tarifa de licencia única por convertir su canal de audio principal a la tecnología HD Radio de iBiquity y el 3% de los ingresos netos incrementales por cualquier subcanal digital adicional. [10] El costo de convertir una estación de radio puede oscilar entre $ 100,000 y $ 200,000. [11] Los fabricantes de receptores pagan regalías. [12]

Si se pierde la señal digital primaria (HD-1), el receptor de HD Radio volverá a la señal analógica, proporcionando así un funcionamiento perfecto entre los métodos de transmisión más nuevos y más antiguos. Las transmisiones extra HD-2 y HD-3 no se transmiten simultáneamente en analógico, lo que hace que el sonido se interrumpa o "salte" cuando la recepción digital se degrada (similar a las interrupciones de la televisión digital). Alternativamente, la señal de HD Radio puede volver a una transmisión más robusta de 20 kilobits por segundo , aunque el sonido se reduce a una calidad similar a la de AM. La transmisión de datos también es posible, con metadatos que proporcionan títulos de canciones o información del artista.

iBiquity Digital afirma que el sistema se acerca al audio con calidad de CD y ofrece una reducción tanto de la interferencia como de la estática; [13] sin embargo, algunos oyentes se han quejado de una mayor interferencia en la banda de AM analógica (ver AM, más abajo).

AM [ editar ]

Un ejemplo de información mostrada por el bloqueo de una estación AM HD.

La versión AM de la tecnología HD Radio en modo híbrido ("MA1") utiliza 30 kHz de ancho de banda (± 15 kHz) y se superpone completamente a los canales adyacentes en ambos lados del canal asignado de la estación. [4] Algunos oyentes nocturnos han expresado su preocupación de que este diseño dañe la recepción de canales adyacentes [14] [15] con una queja formal presentada sobre el asunto: el propietario de WYSL , Bob Savage, contra WBZ en Boston.

Enviar datos digitales a través de un canal de 30 kHz es aproximadamente equivalente a enviar datos a través de dos líneas telefónicas analógicas de 33 kbit / s, lo que limita el rendimiento máximo posible. Al utilizar la replicación de banda espectral, el códec HDC + SBR es capaz de simular la recreación de sonidos hasta 15.000 Hz, logrando así una calidad moderada en la banda AM de ancho de banda estrecho. [16] El modo híbrido HD Radio AM ofrece dos opciones que pueden transportar aproximadamente 40 o 60 kbit / s de datos, y la mayoría de las estaciones digitales AM utilizan por defecto el modo más robusto de 40 kbit / s que presenta redundancia (los mismos datos se transmiten dos veces) .

La señal de radio digital recibida en un receptor de AM convencional sintonizado en un canal adyacente suena como una gran cascada o un silbido similar a un ruido blanco. [ ambiguo ]

AM totalmente digital [ editar ]

El modo totalmente digital ("MA3") permite un rendimiento máximo de 40,2 kbit / s mientras se utiliza un canal de 20 kHz en el contorno de 0,5 mV / m de la estación. Dentro de este contorno, el receptor decodifica las portadoras primaria, secundaria y terciaria, lo que proporciona audio estéreo junto con gráficos (logotipo de la estación y carátula del álbum "experiencia del artista") e información de texto (señal de llamada, título, álbum y artista de la estación). . Más allá del contorno de 0,5 mV / m de la estación, normalmente solo se reciben las portadoras primarias, lo que reduce el rendimiento a 20,2 kbit / s al tiempo que reduce el ancho de banda necesario a 10 kHz. El audio es mono y solo se recibe la información de texto. El menor ancho de banda necesario en el modo totalmente digital en comparación con el modo híbrido reduce la posible interferencia hacia y desde las estaciones que transmiten en canales adyacentes.[17] One tradeoff is the lack of an analog signal for fallback when the digital signal is too weak for the receiver to decode the primary carriers.

Two stations operate in all-digital: WWFD, which has had special temporary authority to do so from the FCC since July 2018,[18] and WMGG, since January 2021 under new rules adopted by the FCC on October 27, 2020, allowing any AM station to voluntarily choose to convert to all-digital operation.[19]

WWFD has experimented with using digital subchannels, operating a second channel at a low data rate while reducing the data rate of the "HD1" channel.[20] 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(.)"[21] The FCC requires stations that wish to multiplex their digital AM signals to request and receive permission to do so;[21] it rejected a bid from WTLC to multiplex in early 2020.[22]

FM[edit]

Play media
HD radio DX during a band opening
HD Radio Transmitter
Spectrum of FM broadcast station without HD Radio
Spectrum of FM broadcast station with HD Radio
Play media
HD Radio EAS Test using KDKA-FM HD1

The FM hybrid digital/analog mode offers four options which can carry approximately 100, 112, 125, or 150 kbit/s of data carrying (lossy) compressed digital audio depending upon the station manager's power budget and desired range of signal. The HD Radio also provides several pure digital modes with up to 300 kbit/s bitrate, and enabling extra features like surround sound. Like AM, pure digital FM provides a "fallback" condition where it reverts to a more robust 25 kbit/s signal.

FM stations have the option to subdivide their datastream into sub-channels (e.g., 88.1 HD1, HD2, HD3) of varying audio quality. The multiple services are similar to the digital subchannels found in ATSC-compliant digital television using multiplexed broadcasting. For example, some top 40 stations have added hot AC and classic rock to their digital subchannels to provide more variety to listeners.[23] Stations may eventually go all-digital, thus allowing as many as three full-power channels and four low-power channels (seven total). Alternatively, they could broadcast one single channel at 300 kbit/s.

Where the digital signal fails, the analog signal is used as a fallback for the main digital channel (normally HD1), requiring synchronization of the two. This requires a significant delay being added to the analog service. Current FCC rules require that one channel be a simulcast of the analog signal. In some cases, particularly during tropospheric ducting events, an HD Radio receiver will lock on to the digital sidebands of a distant station, even though there is a much stronger local analog-only station on the same frequency. With no automatic identification of the station on the analog signal, there is no way for the receiver to recognize that there is no correlation between the two. (Station identification is sent by voice, or as RBDS data, but not all stations use RBDS.) The listener can possibly turn HD reception off (to listen to the local station, or avoid random flipping between the two stations), or listen to the distant stations and try to get a station ID.

Although the signals may be synchronized at the transmitter and reach the receiving equipment simultaneously, what the listener hears through an HD unit and an analog radio played together can be distinctly unsynchronized. This is because all analog receivers process analog signals faster than HD radios can process digital signals. The digital processing of analog signals in an HD radio also delays them. The resulting unmistakable "reverb" or echo effect from playing radios of both types in the same room or house can be annoying. It is more noticeable with simple voice transmission than with complex musical program content. (Multiple HD receivers of the same make and model, or multiple analog receivers in the same room or house, will not cause noticeable echo.)

Stations can transmit HD Radio through their existing antennas using a diplexer as on AM, or are permitted by the FCC to use a separate antenna at the same location, or at a site licensed as an analog auxiliary, provided it is within a certain distance and height referenced to the analog main signal. This limitation assures that the two have about the same broadcast range, and that they maintain the proper ratio of signal strength to each other so as not to cause destructive interference with each other at any given location where they may be received.

Artist Experience[edit]

Automotive entertainment system displaying song metadata including Artist Experience from San Diego's KYXY 96.5 HD2.

HD Radio supports a service called Artist Experience[24] in which the transmission of album art, logos and other artwork can be displayed on the receiver device. Album art and logos are displayed at the station's discretion and require extra equipment. An HD Radio manufacturer should pass the iBiquity certification, which includes displaying the artwork properly.

EAS Alerts[edit]

Since 2016, newer HD radios support Bluetooth and EAS alerts[25] in which the transmission of traffic, weather, AMBER and security alerts can be displayed on the radio. As with Artist Experience, emergency alerts are displayed at the station's discretion and requires extra equipment.

Spectrum of a HD Radio station as shown by a RTL-SDR USB device. The usual bandwidth of a regular FM station is visible as the marker width in the top image.

Bandwidth and power[edit]

FM stations typically require up to 280 kilohertz of spectrum when carrying a stereo transmission. The bandwidth of a FM carrier is found by doubling the sum of the peak deviation (usually 75 kHz) and the highest baseband modulating frequency (around 60 kHz when RBDS is used). Only 15 kHz of the baseband bandwidth is used by analog monaural audio (baseband), with the remainder used for stereo, RBDS, paging, radio reading service, rental to other customers, or as a transmitter/studio link for in-house telemetry.

In regular hybrid mode a station has ±100 kHz of analog bandwidth and adds an extra ±30 kHz guard band and ±70 kHz for its digital signals, thus taking a full 400 kHz of width. FM stations also have the option to discontinue existing subcarrier services (usually at 92 kHz and 67 kHz) in order to carry extended HD Radio, though such services can be restored through use of the digital subchannels that are then made available. However, this requires the replacement of all related equipment both for the broadcasters and all of the receivers that use the discontinued services.

The ratio of power of the analog signal to the digital signal was initially standardized at 100:1 (−20 dBc), making the digital signal 1% of the analog carrier power. Unlike with subcarriers, where the total baseband modulation is reduced, there is no reduction to the analog carrier power. The National Association of Broadcasters (NAB) requested a 10 dB (10×) increase[26] in the digital signal from the FCC. This equates to an increase to 10% of the analog carrier power, but no decrease in the analog signal. This was shown to reduce analog coverage because of interference, but results in a dramatic improvement in digital coverage. Other levels were also tested, including a 6 dB or fourfold increase to 4% (−14 dBc or 25:1). National Public Radio was opposed to any increase because it is likely to increase interference to their member stations, particularly to their broadcast translators, which are secondary and therefore left unprotected from such interference. Other broadcasters are also opposed (or indifferent), as increasing power would require expensive changes in equipment for many, and the already-expensive system has so far given them no benefit.

There are still some concerns that HD Radio on FM will increase interference between different stations even though HD Radio at the 10% power level fits within the FCC spectral mask.[27] North American FM channels are spaced 200 kHz apart. An HD Radio station will not generally cause interference to any analog station within its 1 mV/m service contour, the limit above which the FCC protects most stations. However, the IBOC signal resides within the analog signal of the first-adjacent station. With the proposed power increase of 10 dB, the potential exists to cause the degradation of the second-adjacent analog signals within its 1 mV/m service contour.[28][29][30]

On January 29, 2010, the U.S. FCC approved a report and order to voluntarily increase the maximum digital effective radiated power (ERP) to 4% of analog ERP (−14 dBc), up from the previous maximum of 1% (−20 dBc).[31] Individual stations may apply for up to 10% (−10 dBc) if they can prove it will not cause harmful interference to any other station. If at least six verified complaints of ongoing RF interference to another station come from locations within the other station's service contour, the interfering station will be required to reduce to the next level down of 4%, 2% (−17 dB), or 1%, until the FCC makes a final determination.[32] The station to which the interference is caused bears the burden of proof and its associated expenses, rather than the station that causes the problem. For grandfathered FM stations which are allowed to remain over the limit for their class, these numbers are relative to that lower limit rather than their actual power.

Comparison to other digital radio standards[edit]

HD Radio versus DAB[edit]

Some countries have implemented Eureka-147 Digital Audio Broadcasting (DAB) or its successor DAB+. DAB broadcasts a single station that is approximately 1500 kilohertz wide (≈1000 kilobits per second). That station is then subdivided into multiple digital streams of between 9 and 12 programs. In contrast FM HD Radio which requires 400 kHz bandwidth is assigned to the traditional 200 kilohertz channel spacing used in the United States, with capability of 300 kbit/s in pure digital mode.

The first generation DAB uses the MPEG-1 Audio Layer II (MP2) audio codec which has less efficient compression than newer codecs. The typical bitrate for DAB stereo programs is 128 kbit/s or less and as a result most radio stations on DAB have a lower sound quality than FM does under similar conditions.[33] Many DAB stations also broadcast in mono. In contrast, DAB+ uses the newer AAC+ codec and FM HD Radio uses a codec based upon the MPEG-4 HE-AAC standard.

Before DAB+ was introduced, DAB's inefficient compression led in some cases to "downgrading" stations from stereophonic to monaural, in order to include more channels in the limited 1000 kbit/s bandwidth.[34] Digital radio, such as DAB, DAB+ and FM HD radio currently often have smaller coverage of markets as compared to analog FM, radios are more expensive, and reception inside vehicles and buildings may be poor, depending on the frequencies used. HD Radio shares most of these same flaws (see criticisms below). On the other hand, digital radio allows for more stations and less susceptibility for disturbances in the signal. In the United States, however, other digital broadcast technologies than HD radio (such as DAB+) have not been approved for use on either the FM or AM band.

HD Radio versus DRM[edit]

Digital Radio Mondiale (DRM 30) is a system designed primarily for shortwave radio with compatible radios already available for sale. DRM 30 is similar to AM HD Radio in that each station is broadcast via channels spaced 10 kHz (or 9 kHz in some regions) on frequencies up to 30 MHz. The two standards also share the same basic modulation scheme (COFDM), and AM HD Radio uses a proprietary codec. DRM 30 operates with any of a number of codecs, including AAC, Opus and HVXC. The receiver synchronization and data coding are quite different between HD Radio and DRM 30. As of 2015 there are several radio chipsets available which can decode AM, FM, ([DAB]) HD Radio DRM+ and DRM 30.

Similar to HD Radio, DRM allows either hybrid digital-analog broadcasts or pure digital broadcasts, DRM allows broadcasters to use multiple options:

  • Hybrid mode (digital/analog) - 10 kHz analog plus 5 kHz digital bandwidth allows 5–16 kbit/s data rate;
  • 10 kHz digital-only bandwidth confined to ±5 kHz of the channel center allows 12–35 kbit/s;
  • 20 kHz digital-only bandwidth using ±10 kHz (including half of the adjacent channels) allows 24–72 kbit/s.

DRM+, a different system based upon the same principles, operates in the VHF band with 100 kHz digital-only bandwidth which allows 700 kbit/s data rate.

Actual DRM bit rates vary depending on day versus night transmission (groundwave versus skywave) and the amount of bits dedicated for error correction (signal robustness). For AM stations DRM offers a growth path for broadcasters. Unfortunately DRM shares many of the same flaws as DAB and HD Radio technology: the hybrid mode has shorter broadcast distance compared to an analog AM signal; poor reception inside vehicles and buildings; and interference with adjacent channels when using the 20 kHz mode though in all-digital mode the signal fits inside the designated channel mask.

Digital Radio Mondiale is an open standards system, albeit one that is subject to patents and licensing. HD Radio is based upon the intellectual property of iBiquity Digital Corporation. The United States utilizes DRM for HF or "Shortwave" broadcasts.[35]

Acceptance and criticism[edit]

Awareness and coverage[edit]

According to a survey dated August 8, 2007 by Bridge Ratings, when asked the question, "Would you buy an HD radio in the next two months?" 1.0% responded "yes".[36] Some broadcast engineers have expressed concern over the new system.[37] A survey conducted in September 2008 saw a small percentage of participants that confused HD radio with satellite radio.[38]

Many first-generation HD Radio tuners had insensitive tuners, which caused issues with reception quality. The HD Radio signal is 10 to 20 dB below a station's analog signal. In addition it has been noted that the analog section of some tuners displays inferior reception capabilities compared to older non-digital models.[39]

However, since 2012 HD capable receiver adoption has significantly increased in most newer cars, and several aftermarket radio systems both for vehicles and home use contain HD radio receivers and special features such as Full Artist Experience. iBiquity reports that 78% of all radio listening is done on stations that broadcast in HD.[40] There are an increasing number of stations switching to HD or adding subchannels compatible with digital radio, such as St. Cloud, Minnesota where many local radio outlets find a growing number of listeners tuning in to their HD signals, which in turn has benefited sales.[41]

Different format and compatibility standards[edit]

Even though DAB and DRM standards are open-standards and pre-date HD Radio, HD Radio receivers cannot be used to receive these stations when sold or moved overseas (with certain exceptions; there are HD Radio stations in Sri Lanka,[42] Thailand, Taiwan, Japan, Romania and a few other countries). DAB and DRM receivers cannot receive HD Radio signals in the US. The HD Radio system, which enables AM and FM stations to upgrade to digital without changing frequencies, is a different digital broadcasting standard. The lack of a common standard means that HD Radios cannot receive DAB format broadcasts of other countries and vice versa, and that manufacturers must develop separate products for different countries, which typically are not dual-format. Whereas the AAC (Advanced Audio Coding) family of codecs are publicly documented standards, the HDC codec exists only within the HD Radio system, and is an iBiquity trade secret. Similarly DRM and DAB are open specifications, while iBiquity's HD Radio specification is partly open but mostly private.[43][clarification needed]

HD Radio does not use ATSC, the standard for digital television in the United States. In the days of analog television, the low end of the FM broadcast band (87.7 to 87.9 MHz) overlapped with the audio subcarrier of analog television's channel 6 (which occupied the upper end of the VHF-TV low band); because the NTSC analog-television standard used ordinary analog FM to modulate the audio subcarrier, the audio of television stations that broadcast on channel 6 could be heard on most FM radios. In earlier days of television and radio, several television stations exploited this overlap and operated as radio stations (a process that still continues with some low-powered stations, which are still allowed to broadcast in analog for the time being). Full-powered television stations were forced to cease analog broadcasting in June 2009, with low-powered stations scheduled to cease analog broadcasting by September 2015. Because the digital television and digital radio standards are incompatible with each other, HD radios are not able to receive digital TV signals on the 87.75 MHz frequency, eliminating the former dual-medium compatibility of channel 6 television stations.

Reduced-quality concerns[edit]

Promotion for HD Radio does not always make clear that some of its capabilities are mutually incompatible with other of its capabilities. For example, the FM system has been described as "CD quality"; however, the FM system also allows multiplexing the data stream between two or more separate programs. A program utilizing one half or less of the data stream does not attain the higher audio quality of a single program allowed the full data stream. The FCC has declared "one free over-the-air digital stream [must be] of equal or greater quality than the station’s existing analog signal".[44] (If the FCC discontinues analog simulcasting, each station will have over 300 kbit/s bandwidth available, allowing for good stereo quality or even surround sound audio together with multiple sub-channels, and to a lesser extent more freedom for personal FM transmitters to pair modern smartphones, computers and other devices to legacy analog FM receivers.)

The broadcasting industry is seeking FCC approval for conditional access, that is, enabling the extra programs to be available only by paid subscription (on future models of HD Radio).[citation needed] NDS, a maker of digital media encryption technology, has a deal with iBiquity to provide HD Radio with an encrypted content-delivery system called RadioGuard.[45] NDS claims that RadioGuard will "provide additional revenue-generating possibilities".

A few existing FM tuners tuned to a channel broadcasting a HD Radio signal are prone to increased noise on the analog signal, called "HD Radio self-noise", due to analog demodulation of the digital signal(s). In some high fidelity FM tuners in quality playback systems this noise can be audible and irritating. A few existing FM tuners might require major internal modifications to the internal filters or the addition of a post-detection filter may be required to prevent degradation of the analog signal quality on stations broadcasting with HD Radio.

Reduced analog signal[edit]

Radio stations are licensed in the United States to broadcast at a specific effective radiated power level. NPR Labs recently did a study of predicted HD radio operation if power levels were increased to 10% of maximum power as is now allowed by the FCC under certain circumstances, and found the digital signal would increase RF interference on FM. However the boosted digital HD signal coverage would then exceed analog coverage, with 17% more population covered in vehicles but 17% less indoors.[46]

High costs[edit]

The costs of installing the system, including fees, vary from station to station, according to the station's size and existing infrastructure. Typical costs are at least several tens of thousands of dollars at the outset (including transmitter, diplexer or antenna/feedline, and labor), plus per-channel annual fees (3% of the station's annual revenue[citation needed]) to be paid to Xperi for HD-2 and HD-3 (HD-1 does not have any royalty charge). Large companies in larger media markets (such as iHeartRadio or Cumulus Broadcasting) can afford to implement the technology for their stations. However, community radio stations, both commercial and noncommercial, cannot in many cases afford the $1,000 yearly Xperi fee assessed to LPFM stations. During mid-2010 a new generation of HD Radio broadcasting equipment was introduced greatly lowering the technical costs of implementing the system.

Current HD Radio receivers cost anywhere from around $50 to several hundred dollars, compared to regular FM radios which can sometimes even be found at dollar stores. Although costs have historically been higher for HD Radio hardware, as adoption increases, prices are lowering and receivers containing HD Radio are becoming more commonplace, especially as more radio stations broadcast in HD Radio.[citation needed]

Power consumption[edit]

FM only transmitters will normally operate in a nonlinear class C configuration. This means that the overall transmitter efficiency (AC in to RF out) can be higher than 70%. Digital transmitters need to operate in a close to linear mode which reduces efficiency. A modern hybrid FM/HD transmitter will achieve 50-60% efficiency, whilst a HD only transmitter should manage 40-45%. This leads to significantly increased electricity and cooling costs.

Programming[edit]

Until 2013, the HD Digital Radio Alliance, a consortium of major owners such as ABC, CBS, and iHeartMedia (then known as Clear Channel Communications), acted as a liaison for stations to choose unduplicated formats for the extra channels (HD2, HD3, etc.). Now, iBiquity works with the major owners of the stations to provide various additional choices for listeners instead of having several stations independently deciding to create the same format. HD1 stations broadcast the same format as the regular FM (and some AM) stations, and many of these stations offer one, two, or even three subchannels (designated HD2, HD3, HD4) to complement their main programming.

iHeartRadio is selling programming of several different music genres to other competing stations, in addition to airing them on its own stations. Some stations are simulcasting their local AM or lower-power FM broadcasts on sister stations' HD2 or HD3 channels, such as KMBZ-FM in Kansas City simulcasting 610 KCSP's programming on 96.5-HD2. It is common practice to broadcast an older, discontinued format on HD2 channels; for example, with the recent disappearance of the smooth jazz format from the analog radio dial in many markets, stations such as WDZH in Detroit, Michigan (formerly WVMV), WFAN-FM in New York City, and WNWV in Cleveland, Ohio program smooth jazz on their HD2 or HD3 bands. Some HD2 or HD3 stations are even simulcasting sister AM stations. In St. Louis, Missouri for example, clear-channel KMOX AM (1120 kHz analog and HD) is simulcast on KEZK FM 102.5 HD3. KBCO in Boulder, Colorado uses its HD2 channel to broadcast exclusive live recordings from their private recording studio. CBS Radio is implementing plans to introduce its more popular superstations into distant markets (KROQ-FM into New York City, WFAN into Florida, and KFRG and KSCF into Los Angeles) via HD2 and HD3 channels.

On March 8, 2009, CBS Radio inaugurated the first station with an HD4 subchannel, WJFK-FM in Washington, DC, a sports radio station which also carries sister sports operations WJZ-FM from Baltimore; Philadelphia's WTEL and WIP; and WFAN from New York (though at some point, the WJZ-FM simulcast was replaced with a simulcast of Dallas, Texas sister sports station KRLD-FM).[47] Since then numerous other channels have implemented HD4 subchannels as well, although with nearly 100% talk-based formats because of the reduced audio quality. For example, KKLQ in Los Angeles operates an HD4 signal and aired The Mormon Channel which was 99% talk.[48]

Public broadcasters are also embracing HD Radio. Minnesota Public Radio offers a few services: KNOW, the MPR News station in the Twin Cities, offers music service Radio Heartland on 91.1 HD2 and additional news programming called BBC News and More on 91.1 HD3; KSJN, the Classical MPR station in the Twin Cities, provides Classical 24 service on 99.5 HD2; and The Current, on 89.3 in the Twin Cities, offers Wonderground Radio, music for kids and their parents, on 89.3 HD2.[49]

Southern California Public Radio, heard on 89.3 FM in Los Angeles, offers a digital simulcast of its analog channel on 89.3 HD1 and MPR's music service The Current on 89.3 HD2 in Los Angeles.[50]

WNYC in New York City broadcasts a locally programmed, all-classical music service called Q2, on 93.9 HD2. The service launched in March 2006.[51] On October 8, 2009, the format was moved to WQXR-HD2 on 105.9 when WQXR was acquired by WNYC as part of a frequency swap with Univision Radio for their former frequency. The programming on the WNYC HD2 channel now is a rebroadcast of WQXR in order to give full coverage of WQXR programming in some form, as the 105.9 signal is weaker and does not cover the whole area.

WMIL-FM in Milwaukee has offered an audio simulcast of Fox affiliate WITI on their HD3 subchannel since August 2009 as part of a news and weather content agreement between iHeartRadio and WITI. This restored WITI's audio to the Milwaukee radio dial after a two-month break after the digital transition; as a Channel 6 analog television station WITI exploited the 87.7 FM audio quirk as an advantage in order to allow viewers to hear the station's newscasts and Fox programming on their car radios.

KYXY, operated by CBS in San Diego on 96.5 FM and offers their HD-2 channel as one of the few 'subchannel only' independent Christian music based formats on HD Radio. Branded as The Crossing, it is operated by Azusa Pacific University.

College radio has also been impacted by HD radio, stations such as WBJB which is a public station on a college campus offer a student run station as one of the multicast channels. WKNC in Raleigh, NC, runs college radio programming on HD-1 and HD-2 and EDM WolfBytes Radio on HD-3.

Some commercial broadcasters also use their HD2's to broadcast the programming of noncommercial broadcasters. Bonneville International uses its HD2 and HD3 channels to broadcast Mormon Channel which is entirely noncommercial and operates solely as a public service from Bonneville's owner, The Church of Jesus Christ of Latter-day Saints. That network of eight HD2 and HD3 stations was launched on May 18, 2009 and was fully functional within two weeks. Also, in Detroit, WMXD, an urban adult contemporary station, airs the contemporary Christian K-Love format on its HD2 band (the HD2 also feeds several analog translators around the metropolitan area—see below), due to an agreement between iHeartMedia and K-Love owner Educational Media Foundation allowing EMF to program WMXD's HD2. On a similar note, Los Angeles' KRRL 92.3's HD3 signal rebroadcasts EMF's Air1 and in Santa Barbara KLSB 97.5, which airs K-Love on its primary frequency, rebroadcasts Air1 on HD2 though neither one support 'Artist Experience'.

In July 2018, as part of a projected one year experiment, WWFD in Frederick, Maryland became the first AM station to eliminate its analog transmissions and broadcast exclusively in digital.[52]

Translators[edit]

Although broadcast translators are prohibited from originating their own programming, the FCC has controversially allowed translator stations to rebroadcast in standard analog FM the audio of an HD Radio channel of the primary station the translator is assigned to. This also allows station owners, who already usually own multiple stations locally and nationally, to avoid the rulemaking process of changing the table of allotments as would be needed to get a new separately-licensed station, and to avoid exceeding controlling-interest caps intended to prevent the excessive concentration of media ownership. Such new translator stations can block new LPFM stations from going on the air in the same footprint. Translator stations are allowed greater broadcast range (via less restrictive height and power limitations) than locally originated LPFMs, so they may occupy a footprint in which several LPFMs might have been licensed otherwise.

In addition to the controversial practice of converting the HD Radio-only secondary channels of a primary station into analog FM in areas where the primary station's signal can already readily be received, translators can also be used in a more traditional manner to extend the range of the full content of the primary station, including the unmodified main signal and any HD radio sub-channels, in areas where the station has poor coverage or reception, as is done at K202BD in Manti, Utah, which rebroadcasts both the analog and digital signals of KUER from Salt Lake City. In order to do this, HD Radio may be passed along from the main station via a "bent pipe" setup, where the translator simply makes a frequency shift of the entire channel, often by heterodyning it through the use of an intermediate frequency. This may require an increase in bandwidth in both the amplifier and radio antenna if they are too narrowband to pass the wider signal, meaning one or both would have to be replaced. Baseband translators which use a separate receiver and transmitter require an HD Radio transmitter, just as does the main station. Translators are not required to pass through HD Radio, and the vast majority of existing translators which repeat FM stations running hybrid HD Radio signals do not repeat the HD Radio part of the broadcast due to technical limitations in equipment designed before the prominence of HD Radio.

Receivers[edit]

Automotive and home/professional[edit]

HD-1 signal on KOST 103.5 in a Volkswagen RCD-510 receiver
Sangean HDR-14 portable receiver playing San Diego's KPBS HD-2 channel, Classical 24.

By 2012, there were several HD Radio receivers available on the market. A basic model costs around $50.

The list of HD Radio automotive receiver manufacturers includes Alpine Electronics, Clarion, Delphi Corporation, Directed Electronics, Dual, Harman, Hirschmann Car Communication GmbH (now Part of TE Connectivity), Insignia, Jensen, JVC, Kenwood, Pioneer, Sony (discontinued), and Visteon.

Most car manufacturers offer HD Radio receivers as audio packages in new cars, including Ford, Honda, Hyundai, Kia, Mazda, Subaru,[53] Tesla Motors, Toyota, Volkswagen and, Nissan.

Home and office listening equipment is currently[when?] available from roughly a dozen companies, in both component tuner and tabletop models, including Audio Design Associates, Boston Acoustics (discontinued), DaySequerra, Denon, DICE Electronics, Directed Electronics, Insignia, Jensen Electronics, LG (discontinued), Marantz, McIntosh, Onkyo, Polk Audio, Radiosophy (discontinued), Radio Shack (discontinued), Rotel, Sangean, Sony (discontinued), TEAC, Visteon, and Yamaha.

Portable[edit]

Previously, portable HD Radio receivers were unavailable due to the early chipsets either being too large for a portable enclosure or needing too much power to be practical for a battery-operated device. However, in January 2008 at the Consumer Electronics Show (CES) in Las Vegas iBiquity unveiled a prototype of a new portable receiver, roughly the size of a cigarette pack. Two companies are currently making low-power chipsets for HD Radio receivers: Samsung,[54] and Santa Clara startup SiPort, acquired by Intel in 2011.[55][56]

The portable Coby HDR-700 unit receives AM HD and FM HD stations.[57] Griffin Technology produced an HD Radio tuner designed to be plugged into the dock connector of an Apple iPod or iPhone, with tuning functionality provided via software through the device's multi-touch display. This product is now discontinued.

On July 12, 2009, Best Buy started selling a house brand portable unit, the Insignia NS-HD01, which was the second portable HD Radio to come to the general market and features FM-only playback and a non-removable rechargeable battery which charges via mini USB. Coby produced the first portable HD radio (HDR-700). The Insignia unit sold in 2009 for around $50, the least expensive receiver available,[58] and continues to be sold as of February 2019. By September 2019, Insignia discontinued this unit.

On September 15, 2009, Microsoft released the Zune HD, which includes an HD Radio receiver within the media device.[59] The Zune HD is now discontinued.

iBiquity was trying to get HDR chipsets into mobile phones by 2012.

Open Source Software-Defined Receiver (SDR)[edit]

As of June 10, 2017, a project hosted on GitHub called nrsc5[60] has been created to allow HD Radio reception via rtl-sdr[61] USB devices.

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External links[edit]

  • HD Radio official site
  • U.S. Federal Communications Commission IBOC Page
  • Site with Standards Documents for the NRSC formats of HD Radio
  • My HD Radio - Canadian HD Radio stations
  • WOR Transmitter Tour, containing information on an early IBOC installation
  • Marketing challenges for HD radio
  • Open Geek: HD Radio clips Audio samples of actual HD Radio broadcasts