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First HD Radio RF Upgrades Hit the Market

HD Radio technology may only be starting to climb its adoption curve, but transmission companies plan to showcase products at the NAB Radio Show in San Diego that constitute the first IBOC system upgrade.

HD Radio technology may only be starting to climb its adoption curve, but transmission companies plan to showcase products at the NAB Radio Show in San Diego that constitute the first IBOC system upgrade.

Ibiquity Digital Corp. says its new digital exciter platform answers an industry desire for a DSP-based exciter option and the ability to encode audio and data at the studio end of the system.

Harris and Broadcast Electronics will show products that work with what Ibiquity calls the Exgine, for Exciter DSP Engine technology. Ibiquity employees will talk about the upgrade during the Broadcast Engineering Conference.

“Manufacturers are providing an upgrade path for HD Radio Advanced Application Services. We’re in an industry that’s has been accustomed to product platforms lasting 10 years or more. AAS data applications will be a significant transition requiring flexibility to keep pace with developing data services,” said Jeff Detweiler, Ibiquity broadcast technical manager.

Upgrade path

“The HD Radio exciter manufacturers have taken their first-generation design and Ibiquity has enabled them to migrate to the new Exporter/Exgine configuration,” he said. “This way the manufacturers can continue to build a product today as is and it will continue to work just fine. When the customer decides to move ahead with data services, they can upgrade the appropriate elements.”

Ibiquity engineers considered what a typical FM, seeking to convert to IBOC, wants to send to the transmitter site.

“An FM station needs to send its existing analog signal in an AES format for the HD Radio exciter input,” Detweiler said. “The least amount you would want to send for the analog FM would be 32 kHz. To transmit this linearly, without bit reduction, would require 1.024 Megabits of throughput. That’s what an FM station would send if they wanted to send 15 kHz stereo digital to the transmitter site.”

Most 950 MHz STLs originally were granted a 500 kHz bandwidth allocation; the FCC subsequently reduced it to 300 kHz, he said.

“It allowed enough bandwidth for a 32 kHz sampled AES audio stream, for 15 kHz audio response. But when they reduced it to 300 kHz, that’s when manufacturers started looking at a need for bit-reduced audio.”

Because the HD Radio exciter provides 20 kHz audio response, a station would opt to transmit the signal at 44.1 kHz. To accomplish this would require 1.4112 Megabits per second.

Many stations want to leave their analog air chains intact without changing their infrastructures. They would need separate analog and digital signal paths; thus a station would essentially need the equivalent of two T1 lines, Detweiler said, and still wouldn’t have enough capacity to include the non-audio data and supplementary audio channels of HD Radio.

Ibiquity began an effort to combine the HD Radio coded audio and data on a single transport stream. To accomplish the change, it needed to bring the audio coding and data manipulation back to the studio.

This move is desirable, it believes, because those elements are sourced from the studio.

“Why carry (audio and data) out at full bit rate to the transmitter site and have it be bit reduced in the transmission process?’ Detweiler asked rhetorically.

This new element in the HD Radio system is called the “exporter,” a box that takes the HDC audio coding and Program-Associated Data functions normally associated with the IBOC exciter in the first generation of product, out of the transmitter site and back to studio.

Another element of the Exgine system is an “importer.” BE and Harris showed the importer concept at the spring show. The importer software, which runs on a PC, manages all of the data, whether third-party data, PAD or supplemental channels, for example. It multiplexes the data, plus the encoded HDC information from the digital IBOC signal, and feeds that information as one bitstream to an HD Radio exciter.

Better STL path

The exporter accepts the AES audio for the digital signal as well as the analog signal at 44.1 kHz. It then outputs a signal for the HD Radio STL path that contains both the HDC coded audio and all data services with a throughput less than 300 kilobits per second.

The analog signal is delayed in the exporter for diversity delay, and output at 44.1 kHz. It may then be sent on the existing STL or resampled at 32 kHz and sent with the HDC stream on a multiplexed STL that can fit within the 300 kHz STL allocation.

Ibiquity provides a software developer kit, under license, to HD Radio transmission and automation systems manufacturers. The kit enables them to translate song title, artist and commercial information into the PAD format.

Harris, BE and Nautel believe the changes makes sense.

“They’re splitting the HD Radio system into two pieces,” said Harris Senior FM Applications Engineer Dave Agnew. “They’re moving the HDC codec back to the studio in the exporter. The RF modulation portion stays at the transmitter site. It allows for a bandwidth-efficient bitstream,” he said.

The importer, he said, needs to communicate with the HDC codec portion of the system, so there needs to be communication between the importer and exporter. That is accomplished with an Ethernet link.

BE’s Tim Bealor, vice president of RF Systems, said Exgine is a “new configuration for HD Radio that better accommodates IBOC’s ability to use digital STLs.” The change, he said, conserves the amount of bandwidth required for transport through an STL.

Nautel’s head of development, Tim Hardy, called the upgrade “a big improvement.”

‘Harris is back’

Harris and BE showed elements of this technology at the spring NAB convention.

Since that show, Harris Broadcast has restructured and cut some 100 jobs. It did not exhibit in Philadelphia last year.

“Harris has refocused on the radio market” after having been focused previously on television products, according to Tom Jones, director of Radio Transmission Products. “Harris is back and serious about radio.”

At this show, Harris debuts the first two sellable products from the Flexstar family, the HDI-100 data importer and HDE-100 program exporter. The HDI-100 importer accepts advanced application services, including supplemental audio program streams. The HDE-100 exporter multiplexes the data leaving the importer with a station main program channel and feeds the data as one bitstream to an HD exciter. Both units are compatible with the Dexstar HD Radio exciter.

A Flexstar modulator exciter and STL are planned for April debut, Jones said.

BE’s new high-powered AM transmitter, the 4MX50, to be introduced in San Diego, is designed to work with the Exgine upgrade, said Bealor. The company markets it as an “ultra-efficient” 50 kW unit with a small footprint. He said it’s the first BE unit designed to be compatible with IBOC and its new “Exgine” technology, plus Digital Radio Mondiale, without modification.

With the 4MX50, the exporter function is not in a separate box, but the software is loaded onto a plug-in card that goes into the transmitter. BE will exhibit these cards, as well as the importer. The latter is tied to BE’s AudioVault storage and automation system, but will also work with other audio storage systems, Bealor said.

Hardy of Nautel said Exgine improvements can run on the hardware the company has now. But the company is more focused on its digital adaptive pre-correction in its new M50 digital FM exciter.

“We think the issue of station-to-station interference, on both the AM side and the FM side, is big,” said Angela Hopper, Nautel’s business development analyst. Nautel says the exciter samples the digital or hybrid digital output of the transmitter and dynamically applies pre-correction to help stations stay within their FCC emissions masks without the need to use an extra bandpass filter.

As more stations go IBOC, interference will become a big issue, predicts Nautel President and CEO Scott Campbell. “There are some 100 stations on the air now. As more go on, you’ll see people scream about interference.”

Transmitters without this specific pre-correction capability, he said, could allow an FM station’s signal to interfere with its neighbors through unintended radiation. “This is why we’ve been focused on it,” Campbell said. “If you don’t solve these problems, it’s over.”

Harris and BE say their HD Radio transmitters have the pre-correction capability as well.

Harris will demo its new Split-Level Combining option, its first public demo of this concept since it debuted at the NPR Public Radio Engineering Conference. “We will be monitoring a split system at Quincy – a Z16 HD transmitter and a Z-10 operating into a 6 dB combiner. It’s a standard split-level system,” Agnew said.

Split-Level Combining uses the existing FM transmitter and a new common-amplification FM/HD Radio transmitter to generate the required FM analog power. With the Split-Level Combining System, Harris says, the analog transmitter is no longer required to operate at higher-than-normal power levels to offset combining losses, which results in greater system efficiency and lower monthly operating costs.

Harris has sold about 12 such systems, Agnew said.

The company will also have products from its new lower-power FM HD Radio transmitter line, the Mini-HD series, on hand.

Digital pre-correction explored

Nautel introduced an exciter and several digital transmitters at the spring show: the Jazz, 1,000 W AM transmitter, Maestro FM exciter and Virtuoso 10 kW FM transmitter.

Mike Pappas, chief engineer of KUVO(FM) in Denver, is beta-testing the V10 and plans to speak about how digital adaptive pre-correction works at Nautel’s HD Radio seminar at the Grand Hyatt on Oct. 7, from 6 to 9 p.m.

Hopper said the event is a “no holds barred” kind of experience for attendees, and rather than Nautel giving presentations, executives and attendees participate in a free exchange of ideas.

BE also planned a supplemental digital audio channel demo. The company is sponsoring an HD Radio seminar on Oct. 6, from 1 to 3 p.m. at the Embassy Suites Hotel.

Also at the show, Ibiquity Digital will display an updated station conversion map as well as HD Radio receivers on the market and those upcoming on the automotive and home side.

Clear Channel, Entercom and Cox have committed to convert a substantial number of stations. More groups may announce a stepped up commitment by the show, said an Ibiquity spokesman.