Study Shows ‘Robust’ Coverage for Digital-Only AM

Frank Saxe, Paul Heine, Inside Radio | April 7, 2014

A second round of field testing by NAB Labs and an array of industry players — including station owners, equipment makers and digital radio developer iBiquity — has brought promising results for the prospects of digital-only AM. “What we see with all digital tests is the signal is rock solid,” NAB senior director of advanced engineering David Layer told the NAB Show yesterday in Las Vegas. The latest tests were done using four stations, including Greater Media’s “News Talk 1110” WBT, Charlotte; Cumulus Media’s adult standards KTUC, Tucson (1400); and Beasley’s WNCT, Greenville-New Bern-Jacksonville, NC (1070); as well as iBiquity’s experimental station in Frederick, MD. The stations shut off their analog stations and broadcast only in digital. Engineers driving around the markets then used standard issue digital car radios to analyze how the signals performed. The daytime coverage worked well, and even the more troublesome nighttime coverage was rated as “fabulous” by Layer. “I went into it pretty skeptical,” Cumulus Media SVP/corporate director of engineering Gary Kline concedes. Now his tune has changed, saying the audio quality was “very good” and was easily on par with FM. “It was far better than I had imagined and I walked away from the test feeling pretty good about running HD only mode on AM,” Kline said. Engineers say hybrid mode — broadcasting in both analog and digital — tends to suffer from signal dropout from things like bridges and power lines. “In the all-digital mode there was virtually none of that,” Greater Media VP of engineering Milford Smith said. It was the second round of testing to involve WBT and Smith now believes signal interference is far more critical. Kline said signal drop-off also remains a concern. Layer said NAB Labs plans to do a third round of testing on four additional stations by year’s end to explore more of the engineering what-ifs that AMs face. “We are also developing a test facility to do the kinds of laboratory-based interference tests that need to be done to understand what we’ve seen in the field,” he said. The science is laying the groundwork for a policy decision in Washington. “We want to go to the FCC at some point for authorization of an all-digital service,” Layer said.

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