HD Digital Radio
Everyone has heard of high-definition television (HDTV), and millions of viewers have experienced the vivid picture and lifelike sound in a consumer electronics store, sports bar, or friend’s house—if not in their own home theater. On the other hand, it’s uncommon to find someone who has heard of HD radio, and rare to find someone who has actually listened to one.
HD Digital Radio,1 an upgrade to standard analog AM/FM radio, provides FM-quality sound from AM stations and CD-quality sound from FM stations, all without the hiss, static, and fading commonly experienced with standard radio broadcasts. In addition, HD digital radio includes a text channel that can identify songs and artists in real time, or provide enhanced data services such as news updates, sports scores, or weather forecasts. HD digital radio also enables stations to use multicast channels to broadcast multiple programming options. According to trademark holder iBiquity Digital Corporation,2 the HD in HD Radio does not stand for high definition or hybrid digital, but is part of their brand for digital radio technology.
HD radio stations bundle analog audio with compressed digital audio and textual data, allowing the received signal to be compatible with both analog and HD radios. Using digital in-band on-channel (IBOC)3 technology, the HD radio signal occupies the same radio spectrum as standard radio broadcasts. Digital signals are broadcast as upper and lower sidebands around the analog channel, making optimum use of the available radio spectrum. The two sidebands contain redundant information. The two signals can be combined to provide additional gain, or the stronger signal can be used to minimize adjacent channel and multipath interference. The digital signal is cached to avoid momentary interruptions.
Being a bit of a gadget hound, I ordered an HD radio to try it out. Just after it arrived, our admin announced that she was leaving ADI to rejoin her family in the Midwest. The radio became a going away gift, forcing me to wait patiently for a second one to arrive. The second radio came with three FM antennas: a short wire, a telescoping metal whip, and a longer wire dipole. Initial performance was disappointing; the short wire was useless at my home in the Boston suburbs and the whip received only a few strong HD signals. The dipole worked great, however, allowing reception of more than thirty HD channels. The first thing that I noticed was that the HD signal was “brighter” than the analog signal, with better high-frequency performance and better stereo imaging. My second observation was the complete lack of hiss and background noise.
The thing that made me fall in love with my HD radio, however, was the HD-2 multicast channels. Currently commercial free, these stations compete with satellite radio, but require no subscriptions or other fees. In Boston we’re lucky to have several genres, including rock, jazz, classical, country, and folk—all digital and all commercial free.
Readers: What are your experiences with analog, satellite, or HD radio? Your comments are welcome.
IN THIS ISSUE
The Wit and Wisdom of Dr. Leif—6. From the recently discovered archives of Dr. Leif, Niku Chen has recovered a piece entitled, “Noise Figure and Logarithmic Amplifiers.” Log amps are uniquely equipped as RF measurement elements at frequencies from near-dc to beyond 10 GHz because of their wide dynamic range, temperature stability, excellent log conformance, and ease of use—with measurements provided directly in decibels. Noise figure is a valuable metric when log amps are used in the signal path, as it indicates the system’s ability to extract information in the presence of noise. Despite the antiquity of this document, there is much that is fresh even now, late in the third decade of the 21st century. Read it on page 3.
“Hot Swap,” always a useful confidence factor for anyone contemplating the insertion of a module into a hot socket, is a necessity in high-availability systems, such as servers, network switches, RAID storage, and other forms of communications infrastructure, that must operate with near-zero downtime over their useful life. The article on page 9 gives us an insight into the design and application of hot-swap controllers, key elements of pluggable modules for such systems.
In wireless base stations, the power amplifier (PA) dominates the performance in terms of power dissipation, linearity, efficiency, and cost. Monitoring and controlling the PA makes it possible to maximize the output power while achieving optimum linearity and efficiency. The article on page 14 discusses the elements of a monitoring-and-control solution for the PA using discrete components—and describes an integrated solution.
… AND ON THE BACK BURNER:
In principle, you apply a digital input to a DAC, and it provides an accurate output. In reality, the accuracy of the output voltage is subject to gain- and offset errors from the DAC and other components in the signal chain. The system designer must compensate for these errors in order to produce an accurate output voltage. “Open-Loop Calibration Techniques for Digital-to-Analog Converters,” on page 18, provides some useful suggestions.
The principle of employing a user touch to cause a capacitance change to activate a switch is well understood, but implementing a PCB sensor design with proper shielding and routing poses a challenge. ADI provides a complete capacitive-sensing solution, including controller, evaluation tools, sensor design libraries, and software for the host microcontroller, described in “AC Shield Enhances Remote Capacitive Sensing” on page 18.
Consumer electronics, which tends to be lower frequency and less demanding than typical clock buffering applications, can use inexpensive high-speed op amps as an alternative to traditional clock buffers. High-speed amplifiers are less expensive than traditional clock buffers, yet can accommodate a wide range of designs. “Inexpensive High-Speed Amplifiers Make Flexible Clock Buffers,” on page 19, offers sound advice on this topic.
Dan Sheingold [firstname.lastname@example.org]
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