HD Radio FAQ

HD Radio has been described as “the most significant advancement in radio broadcasting since the introduction of FM stereo.” Instead of relying solely on analog broadcasts, FM and AM stations now also have the ability to broadcast their programs digitally, a change that offers multiple advantages.

• More Programming Options
• Improved Fidelity
• No Audio Distortion
• Advanced Services

HD Radio provides better fidelity than AM or FM. For AM-HD Radio, the difference is striking.

For FM, the improvement in fidelity is somewhat more subtle. FM-HD Radio's big advantage is its ability to multicast -- that is, to carry more than one program service at the same time on the same frequency. This provides stations the ability to triple the amount of programming offered to listeners who have new HD radios and as the technology matures, there may even be four program channels.

Engineers are also working on advanced services like real-time traffic and weather displays. These will have to wait for advanced receivers to be built, but the HD Radio technology fully supports it.

Learn more about the advantages HD Radio will offer. Check into how NPR is implementing HD Radio.

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To enjoy the benefits of HD Radio, you will need to buy a new radio. More and more HD radios are coming on the market, and prices are dropping rapidly. Some good ones are already available under $200. Initially, the receivers were costing $400 or more. Click here for more information on the products currently available.

If you purchase a new HD radio, you will encounter the realities of digital transmission. If you have a digital cell phone or one of the new digital television receivers, you know that digital transmission is "brittle." It's either perfect or not there at all. There is no gentle fading away as in the case of analog. Unlike your digital cell phone or digital television, though, the main channel of HD Radio is designed to simulcast the analog programming. When fading occurs, the digital signal on your radio will blend into the analog signal, so you won't lose service. For the 2nd and 3rd HD Radio channels, however, this “fade protection” will not be available, so you will experience a smaller reliable coverage area for those program services than for the main one.

For some home locations, you may need a better external antenna to pull in the HD digital radio signal. We have other information on our website about getting good reception, which may help with your existing home radio.

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No. The digital program information is embedded within the existing FM signal, so those analog signals will not go away. Our digital signal differs from television’s DTV in this way.

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Yes, HD radios receive traditional analog signals if the station isn't broadcasting HD, and automatically switch to HD when it receives a digital signal.

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Manufacturers such as Radiosophy, Cambridge Soundworks, Sangean, Sony, Boston Acoustic and Radio Shack all have HD tabletop models that receive multiple digital channels alongside analog signals. HD receivers are also available for your car. Prices range from $100 to $500 depending on features.

Here are several links about the various models available and for where to find and buy a digital radio, including the NPR Shop.

• List of HD Radio Receivers available
• HD Radio Receiver Buyers Guide
• NPR Shop

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Not yet, but they are currently in development. The microchip processor at the heart of the receiver consumes a great deal of power to do its job, which means the chipsets in today’s radios require a wall plug, or your car’s battery if it’s a dashboard unit. R&D is currently underway on a battery-operated/portable radio that will be available in the near future.

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No. The HD-1, HD-2 and HD-3 services are free.

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Satellite radio is a subscription service that requires users to pay monthly fees for content delivered to them from networks of satellites. HD Radio broadcasting is commonly referred to as "terrestrial digital radio" because it operates compatibly with the same frequencies AM and FM stations are on currently. And, while you'll need a new receiver to get the new digital content, once you get that the service is free.

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When a radio station broadcasts in HD, the analog FM signal you have always listened to remains exactly the same. The advantage of this new digital technology is that it allows KJZZ to "multicast." That is, we can offer two or more additional programming services on a single frequency. These program offerings are "hidden" on standard radios. An HD digital radio receiver allows you to pick up these "hidden" services. NPR's Jim Zarolli recently reported on HD Radio.

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KJZZ-FM will broadcast its existing analog program service on HD-1, we plan to put Spanish programming on HD-2 and SunSounds reading service on HD-3.

• Analog/HD-1 - News and Information, Jazz
• HD-2 - AHORA a joint venture of Radio Netherlands (RNW) and NPR is a 24-hour Spanish language service.
• HD-3 - SunSounds of Arizona reading service

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To clarify:

KJZZ-FM, Phoenix (91.5)

The following are translators:


• K219DZ Rio Verde, AZ (91.7)
• K292CI Little Acres, AZ (106.9)
• K221EK, Glenwood/Silver City, NM (92.1)
• K255AC, Tucson, AZ (98.9)
• K208AB Flagstaff, AZ (89.5)

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Based on limited experience with this new technology, here is some general information on HD reception. As always, reception depends on proximity to the transmitter site and lack of blocking terrain.

• HD radio reception in vehicles is generally strong.
• HD radio reception in wood-frame homes should be strong.
• HD radio reception in steel-reinforced buildings is problematic, especially on the first floor of such buildings. Reception improves near windows and on higher floors.

Additionally, and this is a very important point, good FM antennas are critical to HD reception. That is the primary reason why vehicle reception is best – they have external antennas. For home or office use at a minimum, a “T” antenna must be attached to the radio with the top of the “T” in a straight line (horizontally or vertically) and with the wire to the receiver perpendicular to the top of the “T” for a foot or two. TV “rabbit ears” should also work as well. With either antenna, a listener should experiment with positioning for best reception.

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Unfortunately, not necessarily: The current digital HD system was designed to offer a service that permits receiving the analog FM signal along with the new digital signals. This requires a careful balance by engineers to establish the power of the digital channels to maximize coverage without interference to the existing analog service. Luckily, it takes much less power for a digital signal to cover a specific listening area than its analog equivalent. In order to provide side-by-side analog and digital service in the FM broadcast band, the power of the digital signals is only 1/100th the power of the analog signal. The KJZZ 91.5 analog signal has a power of 100,000 watts. Our three-channel digital service has a power of only 1000 watts.

Nonetheless, most listeners within the greater KJZZ 91.5 listening area will have good results in receiving our digital signals. Our intention is to share the experiences and recommendations of our engineers and listeners who can suggest ways to successfully receive the KJZZ 91.5 digital channels.

As listeners get to farther locations from our transmitter and try to receive our signal, special techniques may be required to obtain a strong signal.

Listeners close to the transmitter should be able to receive an excellent signal with a properly placed indoor dipole antenna. Factors which will affect successful reception include whether or not a listener's location has a direct line-of-site to the KJZZ 91.5 transmitter, located on South Mountain south of Phoenix, AZ. Generally speaking, locating any FM radio, including an HD radio, on the side of the building facing the transmitter and as high as possible will yield the best results.

An important factor to remember is that an analog FM signal fades gradually as the distance from the transmitter increases. The signal becomes noisier and there is more interference. With a purely digital signal, there will be either perfect sound or no sound. In a strong signal area, the signal will be excellent: no fading, no pops, clicks or hiss, but as the signal drops below a threshold level, the signal disappears completely. In addition, when tuning to a digital signal, it can take up to five seconds to capture the signal so there are several seconds of silence before the station is heard.

To minimize this problem, the HD technology is designed to first capture the analog signal and gently blend to the digital signal when you tune to a station broadcasting its main channel in HD. In areas where the digital signal falls below this critical level, our main channel, KJZZ 91.5, reverts to the analog signal. However, the additional digital channels do not have a corresponding analog signal. Therefore, when the signal falls below a certain level on HD-2 or HD-3, the station will go silent. It may alternate between full sound and no sound depending on the actual signal level. It is important for our listeners to understand this difference between reception of the KJZZ 91.5 main channel signal and the HD-2 and HD-3 digital signals.

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If you are relatively close to our transmitter on South Mountain, check the following:

Did your HD radio come with a dipole antenna?

A dipole antenna can be identified by its shape. It is in the form of a T.

Dipole antennas are inexpensive and available at many electronic retail stores. A dipole antenna captures an FM signal much better than a simple piece of wire. It also receives signals primarily located 90 degrees to the direction of the extended T portion of the antenna. Using the coverage map, determine the approximate direction of the KJZZ 91.5 transmitter, and point the dipole antenna 90 degrees to the direction of the transmitter. Usually the higher the dipole is mounted, the better the reception, and you may need to experiment with several locations. Connect the leads of the antenna to the antenna terminals on the back of the HD radio. Tune in to either HD-2 or HD-3 and listen for awhile to ensure you have a strong signal that can be consistently received.

I am still having problems receiving the KJZZ 91.5 digital signals

Sometimes relocating the receiver or even trying a connection to a TV antenna or rabbit ears will bring in the signal. Some have found an amplified indoor antenna works for them. However, in many cases, the amplified antenna overloads and interference from nearby strong stations prevents reception of distant stations. If this does not produce an acceptable signal and you are a passionate listener to KJZZ 91.5, then it may be necessary to obtain an FM antenna to be mounted in your attic or outside on the roof. FM antennas vary in size and cost depending on the number and type of elements designed to bring in distant signals.

An example of a typical FM antenna

They are available at some local electronic stores or online. You may need to get assistance for the selection of the antenna and its installation from a professional installer.

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iBiquity Digital Corporation is the sole developer of HD Radio technology. With input from radio broadcasters, consumer electronics and broadcast equipment manufacturers, automakers, retailers, and consumers, the company has brought to market an idea that was conceived over a decade ago by scientists and engineers at Westinghouse, CBS, Gannet and Lucent/Bell Labs.

The Federal Communications Commission (FCC) approved HD Radio technology in 2002, and the commercial rollout of the technology began in 2003 when AM and FM stations around the country began digital broadcasts and continued with the launch of HD Radio receivers at the Consumer Electronics Show in January 2004.

For more information go to www.ibiquity.com.

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The "HD" in "HD Radio" is part of iBiquity Digital's brand name for its digital AM and FM radio technology. It does not mean either hybrid digital or high definition, it is simply the branding language for this new technology.

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On the wider sidebands of FM stations, HD Radio can carry multiple streams of FM and/or AM quality. National Public Radio in particular hopes to be able to carry several different streams through the transmitters of member stations, calling its proposed addition to the FM standard "Tomorrow Radio". Some have also proposed using the system to carry surround sound broadcasts with 5.1 channel audio, though this or other multichannel setups reportedly may prevent the fade-to-analog fallback on "hybrid" analog+digital broadcasts. Also, the FCC is still only authorizing multichannel use experimentally to individual stations who ask permission. However it seems to be becoming a de facto standard now that so many stations have adopted it.

Currently, FM stations in the United States and Canada are licensed to occupy approximately 200 kHz of RF spectrum, i.e., the FM band frequency allocations are 200 kHz apart. When a signal modulates the carrier, an infinite number of harmonically-related sidebands are created, and so the actual occupied bandwidth of the signal extends well past the highest modulating frequency (usually ±100 kHz), because of the non-linear nature of frequency modulation. In order to prevent harmful interference to other stations, the carrier frequencies of stations within individual markets are thus assigned on alternate channels; thus they are 400 kHz apart. In addition, the output of the FM transmitter is carefully filtered to limit the RF energy in the sidebands more than 120kHz from the center frequency. In contrast, FM stations have a baseband bandwidth of about 100 kHz, only 15 kHz of which is used by the (analog monophonic) audio.

Analogue stereo uses up to 53 kHz of baseband space, and RBDS is centered at 57 kHz. The "remainder" is currently available for other services, including rental for secondary broadcast services, paging and datacasting, or as a transmitter-studio link for in-house telemetry.

While the various baseband signals all contribute in a complex manner to the total occupied bandwidth (and power demand) of the FM signal, it is important to consider two factors. First, the modulating signal will generate a principal RF component at the fundamental sideband, e.g., a 67 kHz subcarrier will generate RF components at ±67 kHz (and ±134 kHz, etc.) from the FM carrier, and second, any filtering of the modulated signal causes a certain (acceptable according to regulatory bodies as embedded in their frequency and bandwidth assignments) amount of distortion in the received signal, resulting in the formation of intermodulation components from the various modulating signals.

In regular hybrid mode, an HD Radio station has its full ±100 kHz of RF bandwidth, and adds its digital signals into part of the upper and lower adjacent RF channels beyond that, using about 1% of the main FM power level. In extended hybrid mode, the bandwidth of the FM signal is reduced to make way for additional OFDM carriers carrying more data. Because of this, FM stations may have 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 the digital subchannels that are then made available. This will require new receiving equipment for subscribers, however. The current analogue stereo subcarrier would, in theory, eventually be dropped to make more room for digital, and eventually stations could elect to drop the analogue baseband (monophonic audio) completely and go all-digital. However, considering that there are already billions of analogue-only receivers, this is not expected to happen for a very long time, if ever.

There are still some concerns that HD Radio on FM will increase interference between different stations, though it is thought unlikely to make a major difference since HD Radio still fits within the existing spectral mask. It has been confirmed however, that trying to listen to a distant FM station on a channel adjacent to a local HD Radio station can be difficult because of the very poor signal-to-noise ratio created. An HD Radio station will not generally cause interference to any analogue station within its 1mV/m² signal strength contour, the lowest limit above which the FCC protects most stations. In short, some interference of this type is already permitted by FCC assignment rules, and the amount caused by HD Radio is expected to be accepted as well.

As with AM, FM stations transmit using a separate exciter to modulate the very different signals. A combiner is often used, either before common amplification or after separate amplification, though stations are also now allowed to use a separate radio antenna slightly higher or lower on the radio tower. The ratio of power from the analogue to digital signal is 100:1. This means that the digital signal only has 1/100th of the power of the analogue.

http://www.astra2d.com/hdradio.htm

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