Three Voices in Support of Digital Power Hike

NAB TechCheck quotes experiences under experimental authority at Clear Channel, CBS and Greater Media
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A proposed FM digital radio power hike in the United States was the topic in question this week for the editors of NAB’s RadioTech Check. The newsletter talked to broadcast engineering executives at CBS, Clear Channel and Greater Media, quoting them about their experiences with elevated HD Radio power under experimental authority. All three cited positive experiences.

NAB quoted Glynn Walden, senior vice president engineering with CBS Radio, talking about that organization’s experience with KROQ(FM) in Pasadena, Calif., a Class B station at 106.7 MHz:

“KROQ has been operating with a –10 dBc HD Radio digital carrier level for over two years,” it quoted Walden. “As our report to the FCC indicated, the indoor reception has been dramatically improved and the HD Radio digital mobile coverage is consistent with the analog signal. KROQ has two short-spaced second-adjacent channels within the Los Angeles metro and in some locations KROQ is greater than 40 dB stronger than its second-adjacent channel neighbors. Stations operating with elevated IBOC carrier levels are required to meet a tighter Out-of-Band Emissions (OBE) mask. The mask when applied to stations operating with elevated digital carrier power requires an additional 10 dB of OBE suppression. Field tests and the lack of any interference complaints demonstrate that KROQ’s sustained –10 dBc operation has generated no second-adjacent-channel interference.”

The NAB newsletter also quoted Jeff Littlejohn, executive vice president of distribution development with Clear Channel Radio:

“Several Clear Channel engineers had an opportunity to participate in the elevated (–10 dBc) digital carrier tests in New Haven, Philadelphia, Los Angeles and Detroit,” Littlejohn told NAB. “During these tests, we concentrated on observing areas where it was predicted to most likely receive interference. However we did not observe any interference that could be attributed to the elevated digital carrier levels. In New Haven and Los Angeles, Clear Channel provided the ‘host’ station (WKCI and KOST respectively) for the elevated digital carriers. In neither case did Clear Channel receive any complaints of interference.

“The coverage increase that resulted from the elevated IBOC carriers allowed the digital coverage to more closely approach the existing analog coverage,” Littlejohn continued in the NAB article. “Given the significantly increased digital coverage and the absence of any observed interference, it is important that the FCC and the radio industry moves forward expeditiously with broad approval of –10 dBc IBOC carrier levels.”

And NAB also quoted Milford “Smitty” Smith, vice president, radio engineering with Greater Media, about the company’s experiences at two stations:

At WKLB(FM) in Waltham, Mass., Class B, 102.5 MHz: “During December 2008, observations were made at the –10 dBc power level. Extensive driving evaluations, both qualitative and quantitative, showed remarkable improvement in coverage relative to the currently authorized level of –20 dBc. In general, it was observed that the –10 dBc digital signal level approximates or, in some cases, slightly exceeds the coverage of WKLB(FM)’s full-power analog signal.

“Particular care was taken to observe improvements in coverage in areas within 25 miles of the station’s transmitter site,” Smith told NAB. “At the –20 dBc digital power level, there were numerous areas where the digital signal would routinely and predictably fade out due to terrain (referring to gentle rolling hills and valleys in rural areas outside the city of Boston) and man-made obstacles. During the several months of observations, it was apparent that all of these problems disappeared while operating at –10 dBc. There were no instances where the signal was lost in either vehicle in any areas where the signal loss was determined to be a problem at the –20 dBc level.”

At WRAT(FM) in Point Pleasant, N.J., a Class A at 95.9 MHz: “WRAT’s studio and transmitter are located in the coastal region of New Jersey and, as such, are largely surrounded by terrain that is generally very flat and largely devoid of any significant obstructions, especially north and south of the transmitter location,” Smith told the NAB newsletter. “Therefore, the station represents a nearly ‘best case’ propagation scenario for its digital signal. In spite of these optimal conditions, the station, operating at –20 dBc since 2005, has observed a significant abbreviation of its digital coverage as compared to that of its analog facility.

“It appears that an increase in digital power to –10 dBc greatly improves the coverage for a Class A station in relatively flat terrain, both in terms of coverage area and the quality and robustness of that coverage. This is critical, given the sudden and absolute failure mode of the HD Radio signal. Listeners are not likely to tolerate sudden dropouts more than occasionally before seeking an alternate audio source. Further, it appears that a power level very close to –10 dBc will be necessary to fully replicate analog coverage with the digital signal no interference to any FM station was reported or observed during this extended period of operation at the elevated digital power level, including to short spaced WBEN(FM) Philadelphia, also owned by Greater Media.”

The FCC is taking comments on the power increase proposal. The idea remains contentious, and critics oppose any such action, largely citing concerns over interference. The comment period is open until July 17. To file electronically, go to the FCC’s Web site and access the Electronic Comment Filing System. Refer to MM Docket 99-325.

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