Sunday: HD Radio Double Session

Focus Is on Power Increase and Single-Frequency Networks
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As opposed to many other technologies on display at this year's NAB Show, HD Radio technology is, at least relatively, an infant. And compared with more mature technologies, HD Radio technology is in a constant state of development as proponents work to make the technology perform better and give the listener a better experience.

If you have an HD Radio station or are looking at the possibility at installing digital transmission equipment, the Sunday radio sessions at the Broadcast Engineering Conference will be of interest.

There are so many improvements and implementation issues to discuss that conference organizers have scheduled both morning and afternoon sessions.

Dom Bordonaro, chief engineer of Cox Radio Connecticut, is the chairperson/moderator.

"The Sunday sessions are all about HD Radio and include several papers that discuss the next hot topics: the 10 dB power increase and single-frequency networks. Both of these subjects address the desire to extend HD Radio coverage for both the main channel and the secondary channels."

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From a presentation about an FM digital power increase by Jeff Detweiler of iBiquity Digital.
The sessions kick off with "On-Channel Repeater Implementation for HD Radio Coverage Improvement" by Richard Redmond of Harris Corp.

European digital radio facilities use a network of low-power repeaters and "gap filler" transmitters to increase and smooth out coverage. "The gap filler takes the main signal off the air, manipulates it digitally and retransmits on the same channel," says Redmond. "The concept is that we would apply some of this same technology to HD Radio to provide a low-power repeater of the digital side bands to improve performance, and reduce the cost of implementation."

IBOC HD Radio is being tested in Brazil.

Ronald Barbosa of ABERT, the Brazilian Association of Broadcasting, along with Scott Stull of iBiquity Digital Corp., will present a paper on the testing Brazil has done with HD Radio, including a report on the performance of the digital system and the digital signal's compatibility with existing analog signals. It will be interesting to get the perspective from the Brazilian broadcasters on HD Radio.

Their presentation is titled, aptly, "Report From Brazilian Association of Broadcasting About the Tests Results in AM and FM Stations That Use the IBOC Standard."

There is, of course, a proposal before the FCC to allow a power increase of the HD Radio sidebands of FM stations from its present level of –20 dBc to –10 dBc.

Specific challenges are involved in implementing FM HD Radio at the –10 dBc level, and tube transmitters are an alternative to implementing this power increase, in addition to solid-state models. Geoff Mendenhall of Harris will talk about"High-Power, Common Amplification of FM + HD Radio Transmissions with Elevated Sideband Levels."

"The proposed 10 dB increase in HD Radio sideband levels presents a linearity challenge to common amplification of FM and HD Radio signals through a single transmitter," says Mendenhall.

"This paper explains the application of new, high-power, RF amplifier and power supply technologies to elevated HD Radio sideband transmission."

Perhaps you have an FM HD Radio station that depends on a repeater, translator or synchronous transmitter to fill in a few holes in the main station's coverage area. If you maintain these facilities, you know —particularly in the case of synchronous transmitters — that it is extremely important that the signals are in perfect synchronization. This is even more critical with an HD Radio signal.

"FM + IBOC Broadcast Systems Architecture Considerations for Single-Frequency Networks," presented by Philipp Schmid of Nautel, will answer many questions of how to accomplish the goal of synchronization of the HD Radio transmitters.

Good afternoon

George Pletea of 2M Prima Telecom SRL will present "HD Radio Broadcasting in Romania."

Many attendees find it enlightening to learn about the broadcasting regulations in other countries; Pletea's paper will report on the regulatory differences between Romania and the United States and the results of Romania's HD Radio testing. Part of the testing there was to discover the affects of its specific geography on the HD Radio signal.

If you have looked into the power level increase proposal before the commission, you would know that it may be possible, depending on many factors, that some FM HD Radio stations would not be able to implement the full –10 dBc sideband levels, but instead would wind up with a level between –20 dBc and –10 dBc.

"FM Radio Reception in the D.C. Market for Various IBOC Power Levels," presented by Sid Shumate of BIA Financial Network, will explore the effects of increased HD Radio sideband power at various levels on not only HD Radio stations, but also on adjacent stations.

One of the challenges some engineers have encountered with HD Radio installations is how to transport the HD Radio data stream from the studio to the transmitter.

Many stations utilize 950 MHz RF links as studio-to-transmitter links. The fact that these links generally are unidirectional and have rather limited bandwidth restrictions make keeping the HD data synchronized difficult and challenging.

Bob Band and Keyur Parikh of Harris will explore these topics and describe the next generation of 950 MHz RF links in "Optimizing Analog + HD Radio Transport Over an Existing 950 MHz STL Channel."

If you do the math on HD Radio combining, you find that there are real challenges with implementing the possible FM HD Radio sideband power increased to –10 dBc, particularly with system efficiency.

"The 10 dB IBOC injection levels for digital radio have rendered some combining schemes impractical," says Myron Fanton of Electronics Research Inc.

"Lossy systems are too inefficient for the power increase and several new options are discussed, including channel combiners and filters." His paper is "IBOC Combining Schemes for 10 dB Injection."

Additional consideration must be given to meeting the emissions mask, as an increase to –10 dBc may result in increased IM products and spectral regrowth.

Along the same line, Henry Downs and Peter Matthews of Mega Industries will discuss one of the vexing issues when implementing an FM HD Radio station. If you're going on the air at –20 dBc now, what do you do later if an increase to –10 dBc is granted? Throw out your combining system?

"Field-Reconfigurable HD Radio Combiner Provides a Path Forward" will address this situation and what can be done about it, particularly if you have limited space.

As we move deeper into the embedded exporter platform for HD Radio system architecture, we discover that it may be possible to control and create content from many different locations, both local and remote, over IP networks.

Timothy Anderson of Harris will present "Content Management and Control of HD Radio Networks via HD Protocol," which will discuss many possibilities of that protocol.

The final paper of the day, "FM Digital Radio Power Increase — An Update," will be presented by Jeff Detweiler of iBiquity Digital Corp. He will discuss aspects of the proposed increase of the FM HD Radio sidebands to –10 dBc.

He will also be covering the dos and don'ts of the new HD Radio platform, 4.X, which supports the DSP implementation of the embedded exporter. New feature sets and stability improvements of the DSP will be discussed as this technology moves forward.

Thomas R. Ray III, CPBE, is VP/corporate director of engineering for Buckley Broadcasting/WOR Radio, New York.

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