NPR and iBiquity agree: raise HD Radio power four-fold

Expanded from a blog item posted Nov. 5, 2009
By Steve Behrens

NPR joined with the proprietor of HD Radio technology, iBiquity Digital Corp., to propose that the FCC quadruple the maximum power level of digital FM signals.

In the logarithmic measures favored by engineers, this would be a 6 dB power boost, from -20 dBc to -14 dBc.

Pushed by the FCC to present a joint proposal, NPR and iBiquity went to the commission Nov. 5 with a compromise that they said would significantly improve reception of the digital HD Radio signal without damaging regular analog FM reception.

In hybrid analog/digital HD Radio broadcasts, the digital signal’s power is now limited to 1 percent of the analog signal’s, but that means the digital signal is harder to receive, especially indoors, than regular FM.

Last year a number of commercial broadcasters proposed that the FCC remedy the problem by raising the maximum digital power tenfold to 10 percent of the analog signal’s level. But NPR pointed to field tests indicating that such a big boost would hurt analog FM.

If adopted by the FCC, the compromise fourfold digital power increase would be authorized automatically for all HD Radio stations, according to Mike Starling, executive director of NPR Labs, while many other stations could raise digital power as much as tenfold in locations where adequate distances between stations would limit interference.

Days before the joint proposal to the FCC, the publication Radio World posted an article on its website by engineers with iBiquity and Boston-area station owner Greater Media who argued that the full tenfold increase will be necessary for good, uninterrupted reception indoors and in cars.

Though NPR and many pubradio stations have been fans of HD Radio, stations also want to protect the radio reading services for the sight-impaired. Both HD Radio and the reading services are carried on sidebands on the outer edges of the FM channel where they’re most vulnerable to conflicts with signals on nearby frequencies. Starling said last week’s iBiquity/NPR proposal says the collaborators will work to develop a treatment—putting the HD Radio signal on the sideband farther away from the radio reading service. NPR and iBiquity also said they’ll work to develop single-frequency networks to fill gaps in HD Radio coverage. 

Copyright 2009 by Current LLC

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More power for HD Radio means more buzz on analog FM, NPR finds, September 2008.

HD Radio gives WAMU listeners more slices of pie to go around, says General Manager Caryn Mathes.


Starling, NPR Labs Senior Technologist John Kean and Towson University (Md.) Prof. Ellyn Sheffield spoke on the HD Radio findings at the Association of Public Radio Engineers' Public Radio Engineering Mini-Conference Sept. 22. Here's an audio-and-slideshow webinar on the Advanced IBOC Coverage and Study.

Why the Full 10 dB Increase Is Necessary, by Russ Mundschenk, iBiquity Digital Corp., and Milford Smith, Greater Media Inc. On RadioWorld site, Oct. 20.

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