Field testing resumes for radios digital best hope
Originally published in Current, Aug. 16, 1999
By Steve Behrens
Testing has begun again on technologies that may allow radio broadcasters to put out digital audio signals--along with yet-to-be-developed data services--without having to find new frequencies or buy new antennas.
Public radio station WBJB-FM in Lincroft, N.J., an early test site, became the first station to air a hybrid signal containing both digital and analog signals through a single antenna and a regular radio channel.
Three companies are proposing systems for digital audio broadcasting (DAB):
- Lucent Digital Radio, which claims the first at WBJB, began testing there in April in cooperation with Armstrong Transmitter Co. and plans to expand tryouts to several stations in the mid-Atlantic states.
- USA Digital Radio Inc. (USADR), owned by the major radio chains, will soon begin testing at a dozen stations across the country, including public WETA-FM in Washington, D.C.
- Digital Radio Express, a young San Jose, Calif., company that claims especially dramatic improvement in AM quality, has begun testing at Bay Area stations, according to Norman Miller, the company's president.
The proponents agreed this spring to submit test results to the industry standards panel, the National Radio Systems Committee, on Dec. 15. Later, the committee is supposed to recommend a system to the FCC. Optimists hope for a national standard by mid-2000 and digital radios in stores by Christmas 2000.
USADR, for now, has the lead in clout, if industry politics count for anything at the FCC. Founded in 1991 by CBS, Gannett and Westinghouse, USADR added 13 major broadcasters as equity owners earlier this year. Its owners now count among themselves half of the radio industry's revenues and all of the 10 largest companies.
As terrestrial radio stations awaits new competition from 100-channel digital satellite services, the new testing may decide whether the stations can go digital within their own AM and FM spectrum--"in-band, on-channel" (IBOC)--or whether they're thrown into a daunting competition for additional spectrum.
"This is the last round for IBOC, I would say," says Don Lockett, NPR's chief technology officer and a member of the National Radio Systems Committee. Earlier field tests "determined that none of the systems met the requirements necessary to replace today's technology," Lockett told Current. "On inexpensive receivers, analog and digital signals were not isolated enough to prevent intermodulation between the two."
"Based on what I learned in the first round of testing," Lockett adds, "it has to work [in the new round of tests] or we have to move on to something else."
To George Marshall III, chief engineer at WBJB, the Lucent tests sound "real good." Marshall says he asked some "very critical listeners" who live beyond his station's normal coverage area whether they had heard any degradation of WBJB's signal during Lucent's testing, and they haven't.
What worries Marshall is that the FCC's low-power FM proposal (story, page 1) could crowd more stations into the spectrum, creating greater interference with the digital signals. "If [LPFM] becomes a reality, this goes away," he predicts.
Going digital won't balloon radio's capacity quite as dramatically as it has for TV, but proponents do promise major gains. USADR claims its system will expand FM's frequency response from 12 kilohertz to 20, and AM's from 4 kHz mono to 12 kHz stereo, while reducing static on AM and multipath interference on FM.
DAB's bigger capacity gains will show up when most Americans have bought digital radios and the analog signal can be dropped. The new capacity gives broadcasters an incentive to speed up their transition to digital, says E. Glynn Walden, USADR's v.p. of broadcast engineering and CBS Radio's director of engineering. "That's the carrot, rather than the FCC mandate."
The industry may choose to use some of the capacity to transmit six-channel surround sound, which DVD, digital TV and other digital delivery systems already incorporate.
There are also endless options for delivery of text or other data, titles of songs, weather reports, sports scores, or even Internet data. If the excess capacity of several stations were sold as a package, it could create quite a wide pipe for wireless Internet delivery, suggests Eric Hoehn, chief engineer at WETA-FM.
Transition costs will be lower than for digital TV. A station will need to buy at least a new exciter for its transmitter and a new studio-to-transmitter link, and possibly a whole new transmitter. Costs will range from $70,000 to $190,000, USADR estimates.
But there may be cost savings down the road. After consumers go digital and the analog signals are turned off, stations can greatly reduce their transmitter power costs. Lucent's digital signal covers the same area with 50 watts that WBJB's analog signal covers with 500 watts, says George Marshall III, chief engineer at the station.
USA Digital Radio
"Lucent essentially has an uphill battle," boasts Walden of USADR. "The patents we need to avoid interference, we already have in our pocket." So is much of the radio broadcasting industry, starting with USADR's CBS/Westinghouse founders.
The company, based in Columbia, Md., petitioned FCC last October to accept its technology as the DAB standard. In April, USADR announced that Broadcast Electronics, Harris Corp. and three other transmitter manufacturers had successfully passed AM and FM waveforms through their equipment
USADR appears to be selecting stations to test for interference between adjacent channels, says Hoehn. He expects that USADR will deliver an additional transmitter for testing at WETA next month.
A major difference between USADR's and Lucent's systems is in their handling of weak signals and interference, which can destroy reception, especially in a moving car.
The proponents use different digital compression systems to squeeze a digital signal and extensive error-correction data into a radio channel, along with the analog signal. USADR's technology, developed by AT&T and the Fraunhofer Institute, reduces the 1.5 megabits/second stream from a compact disc to 96 kilobits/second.
Compression allows USADR to transmit the data twice within the signal, so that the receiver can discard corrupted data and use the good parts. As a last resort, Walden says, the USADR system switches to analog reception rather than allowing the sound to degrade or drop out.
Lucent Digital Radio
The other major proponent, based in Warren, N.J., is a venture of Lucent Technologies, a major spin-off of AT&T (along with its related Bell Labs).
Lucent Digital Radio will push for side-by-side comparison tests between the competing DAB systems, like the ones used in testing HDTV and DTV systems, says Nick Karter, LDR's v.p. of business development.
"This is a great opportunity to do this the right way," says Karter. "It doesn't make sense to submit testing if the reference points are entirely different." But the additional step may also lengthen the timetable for standards-setting.
Like USADR, Lucent will compress CD-quality audio into a 96 kilobits-per-second bitstream, and will use error correction. Its "multi-streaming" technology divides and rearranges the audio data so that the listener can still hear programming at reduced quality even if the receiver loses most percent of the signal when the listener drives under a bridge, according to Marshall.
But if broadcasters prefer, Karter says, the system could be redesigned so that a severely distressed digital signal would default to analog, as USADR's system does.
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