HD Radio

HD Radio, which originally stood for "Hybrid Digital", is the trademark for iBiquity's in-band on-channel (IBOC) digital radio technology used by AM and FM radio stations to transmit audio and data via a digital signal in conjunction with their analog signals. It was selected by the United States Federal Communications Commission (FCC) in 2002 as a digital audio broadcasting method for the United States, and is the only digital system approved by the FCC for digital AM/FM broadcasts in the United States. It is officially known as NRSC-5, with the latest version being NRSC-5B. Other digital radio systems include FMeXtra, Digital Audio Broadcasting (DAB) (Eureka 147), Digital Radio Mondiale (DRM30 and DRM+ configurations), and Compatible AM-Digital (CAM-D).

As a standard practice, the kilohertz signal rate is written next to its corresponding data transfer rate kilobits/s or kbits/s in HD Radio documentation. While HD Radio does allow for an all-digital mode, this system currently is used by some AM and FM radio stations to simulcast both digital and analog audio within the same channel (a hybridized digital-analog signal) as well as to add new FM channels and text information. Although HD Radio broadcasting's content is currently subscription-free, listeners must purchase new receivers in order to receive the digital portion of the signal. As of May 2009, there were more stations in the world on the air with HD Radio technology than any other digital radio technology. More than 1,900 stations covering approximately 84% of the United States are broadcasting with this technology, and more than 1,000 HD2 and HD3 multicast channels are on the air. According to iBiquity's website, the "HD" is simply a brand name and has no meaning. There is no connection with high-definition television (HDTV), although like HDTV the HD Radio specification provides enhanced capabilities over the old analog format, such as 5.1 surround sound.

The FCC has not indicated any intent to force off analog radio broadcasts as it has with analog television broadcasts, as it would not result in the recovery of any radio spectrum rights which could be sold. Thus, there is no deadline by which consumers must buy an HD Radio receiver. In addition, there are many more analog AM/FM radio receivers than there were analog televisions, and many of these are car stereos or portable units that cannot be upgraded.

Overview

Digital information is transmitted using COFDM with an audio compression algorithm called PAC (Perceptual audio coder). However, audio compressed with this method led to complaints about poor sound quality, so in 2003 iBiquity combined it with an enhancer called SBR (spectral band replication) that improves audio quality at very low bit rates and branded the codec to HDC (High-Definition Coding). (HDC is a proprietary codec based upon, but incompatible with, the MPEG-4 standard HE-AAC). HD Radio equipped stations pay a one-time licensing fee for converting their primary audio channel to iBiquity's HD Radio technology, and 3% of incremental net revenues for any additional digital subchannels. The cost of converting a radio station can run between $100,000 and $200,000. Receiver manufacturers pay a royalty.

If the primary digital signal is lost the HD Radio receiver will revert to the analog signal, thereby providing seamless operation between the newer and older transmission methods. The extra HD-2 and HD-3 streams are not simulcast on analog, and thus are totally lost when digital reception is gone. Alternatively the HD Radio signal can revert to a more-robust ~20 kilobit per second stream, provided the broadcaster has that set up as well. Datacasting is also possible, with metadata providing song titles or artist information.

iBiquity Digital claims that the system approaches CD quality sound and offers reduction of both interference and static; however, some listeners have complained of increased interference on the AM band (see AM, below).

AM

An example of information displayed by an AM HD station locking.

Sending pure digital data through the approximately 20 kilohertz AM channel is roughly equivalent to sending data through two 33 kbit/s analog telephone lines, thus limiting the maximum fidelity possible. By using spectral band replication the HDC+SBR codec is able to simulate the recreation of sounds up to 15,000 Hz although most consumers can tell it is recreated and feel it is artificial sounding. The HD Radio AM hybrid mode offers two options which can carry approximately 40 or 60 kbit/s of data, but most AM digital stations default to the more-robust 40 kbit/s mode which features redundancy (same signal broadcast twice). HD Radio also provides a pure digital mode, which lacks an analog signal for fallback and instead reverts to a 20 kbit/s signal during times of poor reception. The pure digital mode transmissions will stay within the AM station's channel instead of spilling into the channels next to the station transmitting "HD radio" as the hybrid digital stations do although there are currently no AM stations broadcasting this pure digital sigal and it is doubtful any ever will as that would mean no reception on any analog receiver which currently describes 99.99% of AM receivers in North America.

The AM version of HD Radio technology uses the 20 kHz channel (+/- 10 kHz), and overlaps 10 kHz into the opposite sideband of the adjacent channel on both sides. When operating in pure digital mode which is not used here in North America, the AM HD Radio signal fits inside a standard 20 kHz channel (20-40 kbit/s) or an extended 30 kHz channel (40-60 kbit/s), at the discretion of the station manager. As AM radio stations are spaced at 9 kHz (Europe) or 10 kHz (Americas) intervals, much of the digital information overlaps adjacent channels when in hybrid mode. Many nighttime listeners have expressed concern that this design harms reception of adjacent channels with one formal complaint filed regarding the matter: WYSL owner Bob Savage against WBZ in Boston. The digital radio signal received on a conventional AM receiver tuned to an adjacent channel sounds like white noise but no where near as inconspicous, as can be heard in the audio soundclip referenced in the previous sentence. Listeners (and some professional broadcasters) call it IBUZ instead of the legal term, IBOC because of the "buzz saw" like noise. This is by far the most charitable name that it has been called by it's opponents.

FM

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

The FM hybrid digital/analog mode offers four options which can carry approximately 100, 112, 125, or 150 kbit/s of lossy data depending upon the station manager's power budget and/or 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. Stations may eventually go all-digital, thus allowing as many as three full-power channels and four low-power channels (seven total). As defined by iBiquity these channels could be sub-divided into CD-quality (100 kbit/s), FM-quality (25-50 kbit/s), AM-quality (12 kbit/s), or Talk-quality (5 kbit/s) channels. 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. 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. Because there is no standard identification or other indication sent on the analog signal, there is no way for the receiver to recognize that there is no correlation between the two. The listener can possibly turn HD reception off (to listen to the local station, or avoid random flipping between the two stations), or enjoy listening to the distant stations and trying to get a station ID.

Although the signals may be synchronized at the transmitter and reach your equipment simultaneously, what you hear through an HD unit and an analog radio played together will be distinctly unsynchronized. This is because all analog receivers process analog signals faster than HD radios can process digital signals. The resulting unmistakable "reverb" or echo effect from playing HD and analog in the same room or house can be annoying. It's more noticeable with simple voice transmission than with complex musical signals. (Multiple HD receivers or multiple analog receivers in the same room or house will not cause noticeable echo.) The only way to truly "synchronize" HD with analog radio would be to delay the analog transmission by a few hundred milliseconds, but this is normally not done.

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.

Bandwidth and power

Currently, FM stations in the United States and Canada are licensed to carry 100 kilohertz of bandwidth, requiring approximately 200 kilohertz of spectrum. Only 15 kHz of the modulation 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 its full ±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 is 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 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 have also been tested, including a 6dB or fourfold increase to 4% (−14dBc or 25:1). National Public Radio is 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. 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 10dB, the potential exists to cause the degradation of the second-adjacent analog signals within its 1 mV/m service contour. Ironically, the National Association of Broadcasters claims this is not a problem, at the same time using it as justification to keep LPFM stations off the air on second-adjacent channels, excluding NAB members' own translators that are allowed higher power than local community radio LPFMs.

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 (−14dBc), up from the previous maximum of 1% (−20dBc). Individual stations may apply for up to 10% (−10dBc) if they can prove it will not cause destructive 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% (−17dB), or 1%, until the FCC makes a final determination. 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

FM HD Radio versus DAB

Some countries have implemented Eureka-147 Digital Audio Broadcasting (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 is assigned to the traditional 200 kilohertz-wide channels, with capability of 300 kbit/s in pure digital mode. Thus HD Radio is approximately twice as data-efficient as DAB.

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 programs is only 128 kbit/s and as a result most radio stations on DAB have a lower sound quality than FM, prompting a number of complaints. The newer FM HD Radio uses a codec based upon the MPEG-4 HE-AAC standard. It has been claimed this can achieve the same perceived quality as DAB MP2, but at one-quarter the bit rate (CD quality at 64 kbit/s; FM quality at 48 kbit/s).

A directly related issue with DAB's original inefficient compression is "downgrading" stations from stereophonic to monaural, in order to include more channels into the limited 1000 kbit/s bandwidth, smaller coverage of markets as compared to analog FM, radios that are overly expensive, poor reception inside vehicles or buildings, and a general lack of interest in DAB in many countries. HD Radio shares most of these same flaws (see criticisms below).

AM HD Radio versus DRM

Digital Radio Mondiale (DRM) is a system designed primarily for world band radio with compatible radios already available for sale. DRM is very similar to AM HD Radio in that each station is broadcast via a channel 20 kilohertz wide (+/-10 kHz), and the radio is hand-tuned to each individual station's location on the dial. The two standards also share the same modulation scheme (COFDM) and codecs based upon MPEG-4 AAC.

Just like HD Radio which 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 (equal to one-half of one channel) allows 12-35 kbit/s;
• 20 kHz digital-only bandwidth (equal to one channel with both sidebands) allows 24-72 kbit/s.

DRM+ additionally permits operation in the FM 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. For AM stations DRM offers a growth path for broadcasters. Unfortunately DRM shares many of the same flaws as DAB and HD Radio technology: shorter broadcast distance as compared to analog AM signal when in hybrid mode; poor reception inside vehicles and buildings; and interference with adjacent channels (though in all-digital mode the signal fits inside the designated channel mask).

Criticisms

Awareness, coverage

There is low awareness among consumers, and even lower uptake. 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?" only 1.0% responded "yes". Some broadcast engineers have also expressed distrust or dislike of the new system. Also, a survey conducted in September 2008 saw a small percentage still confused HD radio with satellite radio.

Most of the first-generation HD Radio tuners have been noted as being very insensitive, making reception problematic. 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 poor reception capabilities compared to older non-digital models.

Proprietary and incompatible

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, Brazil, Thailand, Taiwan, Japan 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.

HD Radio is also incompatible with 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 allowed the audio of television stations that broadcast on that channel to be heard on most FM radios. 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. 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 87.7 frequency, eliminating the dual-medium compatibility of channel 6 television stations.

Reduced-quality concerns

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". (If the FCC discontinues analog simulcasting, each station will have over 300 kbit/s bandwidth available, allowing for CD-quality or even surround sound audio together with multiple sub-channels.)

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). Conditional access will also enable special services for the blind (such as radio reading services) and hearing impaired. 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. NDS claims that RadioGuard will "provide additional revenue-generating possibilities".

A few existing FM tuners tuned to a channel broadcasting an HD Radio signal are prone to increased noise on the analog signal, called "HD Radio self-noise" ([1]), due to analog demodulation of the digital signal(s). Some rare high fidelity FM tuners in quality playback systems, cause this noise to be audible and irritating. A few, existing FM tuners, might require major internal modifications to the internal filters ([2]) or the addition of a post-detection filter ([3]) may be required to prevent degradation of the analog signal quality on stations broadcasting with HD Radio.

Reduced analog signal

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.

High costs

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 to be paid to iBiquity. Large companies in larger media markets (such as Clear Channel or Citadel Broadcasting) can afford to implement the technology for their stations. However, community radio stations, both commercial and noncommercial, cannot. 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 (US), compared to regular FM radios which can even be found at dollar stores. By contrast, all of the R&D work for DAB (and much of DAB+) had already been done using an existing codec, and requires no licensing fees. FMeXtra is even less expensive, and requires no installation labor or cost for the broadcaster, other than plugging it into the transmitter. It also requires no FCC approval, coming under a station's subsidiary communications authority. FMeXtra requires no license fees, and does not interfere with adjacent channels. Other digital broadcast technologies have not been approved for use in the United States. The number and cost of HD Radio receivers greatly dropped during 2009 and 2010.

Programming

Currently the HD Digital Radio Alliance, a consortium of major owners such as ABC, CBS, and ClearChannel, is acting as a liaison for stations to choose unduplicated formats for the extra channels (HD2, HD3, etc.). This is designed to provide additional choices for listeners instead of several stations all independently deciding to create the same format. HD1 stations broadcast the same format as the regular FM (and some AM) stations, and most of these stations offer an HD2 subchannel to complement their current programming.

Clear Channel 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 98.1-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), WQCD in New York City, WPGB in Pittsburgh, Pennsylvania and WNWV in Cleveland, Ohio program smooth jazz on their HD2 or HD3 bands. Other recent additions include introduction of air staff on HD2 stations, like KDWB's Party Zone channel in Minneapolis-Saint Paul. 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 recently announced plans to introduce its more popular superstations into distant markets (KROQ 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 WIP and WFAN from New York.

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.

Southern California Public Radio, heard on 89.3 FM in Los Angeles, offers Ahora, the Spanish-language service of Radio Netherlands on 89.3 HD2 and MPR's music service The Current on 89.3 HD3 in Los Angeles.

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. 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 Clear Channel 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.

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.

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 Clear Channel and K-Love owner Educational Media Foundation allowing EMF to program WMXD's HD2.

Translators

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 a HD Radio channel of the primary station the translator is assigned to (see, for instance, W237CS, which is licensed as a translator to WXMT but originates its own schedule). 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

Automotive and home/professional

There are as many as 100 different HD Radio receivers to choose from, far more than are available to receive any other digital radio signal. Receivers are becoming less expensive, starting at around US$50. Manufacturers have initially focused on making car stereos. In 2008, Ford Motor Company became the first U.S. automaker to feature HD Radio tuners in its vehicles; starting with the 2009 model year, Ford began offering HD Radio tuners as a factory-installed option (Compatible with SYNC), and was upgraded to standard on all of its brands for the 2011 model year. BMW offers Factory-Installed HD Radio on nearly all 2008+ models. Hyundai offers factory-installed HD Radio on the Genesis 2008+ model year. Mercedes-Benz offers factory-installed HD Radio on the R320, ML320 and GL320 models (2009 model year). MINI offers factory-installed HD Radio on the Cooper, Cooper S (2008+ model year). Scion offers HD Radio on select audio systems. Volvo offers factory-installed HD Radio on the S40 T5, V50 T5, C30, C70, S80, V70, XC60, XC70 and XC90 models (2009 model year).

The growing list of HD Radio automotive receiver manufacturers includes Alpine Electronics, Clarion, Delphi Corporation, Directed Electronics, Dual, Insignia, Jensen, JVC, Kenwood, Pioneer, Sony and Visteon.

Home and office listening equipment is currently available from many companies, in both component tuner and tabletop models, including Audio Design Associates, Boston Acoustics, DaySequerra, Denon, DICE Electronics, Directed Electronics, Insignia, Jensen Electronics, LG, Marantz, Onkyo, Polk Audio, Radiosophy, Radio Shack, Rotel, Sangean, Sony, TEAC, Visteon and Yamaha.

Portable

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 and SiPort.

The portable Coby HDR-700 unit receives AM HD and FM HD stations. Griffin Technology produces 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.

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 sells for around $50 and is the least expensive receiver currently available.

On September 15, 2009, Microsoft released the Zune HD, which includes an HD Radio receiver within the Organic light-emitting diode-screened media device.

The radio industry is trying to get HDR chipsets into mobile phones by 2012.

External links

• HD Radio official site
• U.S. Federal Communications Commission IBOC Page