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HD Radio Technology: AM/FM Spectrum and Stations Explained

hd radio radio station am fm spectrum digital broadcasting

Let’s delve into the world of HD Radio technology, covering its features, how it works, and the specifics of HD Radio stations, including the AM and FM spectrum they utilize.

In the past, radio broadcasting was purely analog. But with technological advancements, we now have HD Radio, which aims to provide superior sound quality and a host of extra features. All you need is an HD Radio tuner installed in your car, and you’ll potentially have access to hundreds of programs and thousands of radio stations.

HD Radio™ and HD are proprietary trademarks of “iBiquity Digital Corporation”.

HD Radio Features

Here’s a breakdown of what HD Radio technology offers:

Digital AM and FM: Experience radio in a digital format.
More HD Radio Stations: Enjoy a wider selection of stations while driving or at home.
Digital Sound Quality: Get crystal-clear audio without static, hiss, or pops.
No Subscription Fees: No monthly charges to worry about.
No Data Charges: Unlike streaming services, HD Radio doesn’t use your mobile data.
Multiple Active Channels: Tune into up to four different channels from a single station.
Studio-Like Clarity: Receive a clear signal in your car, almost as if you were in the studio.
Station Information: HD Radio stations display station IDs, artist names, and more.
Extensive Network: The HD Radio network offers a wide range of new programs and thousands of stations.
Real-time Information: HD Radio receivers can provide shopping cart of the songs you love, real-time traffic updates, weather forecasts, news updates, sports scores, and even fuel prices at nearby stations.

How HD Radio Technology Works

HD radio stations

Multiple Channels: Each HD station can carry up to three additional radio channels, offering more listening options (HD1, HD2, HD3, HD4).
Digital Broadcasting: HD Radio stations can broadcast both audio and data using digital signals.
In-Band On-Channel (IBOC): This digital signal is embedded on a standard radio station’s analog signal using a concept called In-Band On-Channel (IBOC).
OFDM Subcarriers: Two OFDM subcarrier sets are superimposed above and below the analog carrier center frequency. Based on subcarrier scaling, different modes exist, including hybrid, extended hybrid, and all-digital.
Receiver Compatibility: Receivers can listen to both the standard analog channel and the HD channel.
Frequency Ranges: HD Radio stations use carrier frequencies in the range of 535 KHz to 1705 KHz for AM broadcasting and 88 to 108 MHz for FM broadcasting.

HD Radio AM and FM Spectrum

Here’s a visual representation of the HD Radio AM and FM spectrum:

HD radio AM spectrum

Figure 2 shows the HD Radio AM spectrum. Primary channels exist from 10 to 15 KHz, and secondary channels exist from 5 to 10 KHz above and below the analog carrier frequency.

OFDM (Orthogonal Frequency Division Multiplexing) modulation is used for the digital spectrum above and below the analog signal. Complex modulation schemes like BPSK, QPSK, 16-QAM, and 64-QAM are used to map data onto the subcarriers of the OFDM spectrum.

The FCC (Federal Communications Commission) specifies power spectrum masks for both AM and FM spectrums for HD Radio. These masks define the power emission limits for both spectrums, ensuring that all HD Radio stations comply with these emission requirements.

Read Document No. SY_SSS_1026s for the HD Radio FM spectrum mask and Document No. SY_SSS_1082s for the HD Radio AM spectrum mask specifications, published by the NRSC (National Radio Systems Committee).

HD radio FM spectrum

Figure 3 illustrates the HD Radio FM spectrum. OFDM is transmitted along with the analog carrier, either above or below the reference radio carrier frequency.

OFDM subcarriers start at approximately +/- 101 KHz from the analog carrier and are located up to +/- 198 KHz from the analog carrier center frequency. Digital modulation techniques like QPSK are used to carry more bits per subcarrier. For example, QPSK carries 2 bits per subcarrier, 16QAM carries 4 bits per subcarrier, and so on.