Airwaves: August 1, 2008
Greater coverage for HD Radio?
Ever since the Federal Communications Commission allowed radio stations to send digital signals along with their regular analog broadcasts, there has been great debate as to just how well - or how poorly - the system, called HD Radio, works.
Fans point out that the sound is cleaner, in that there is reduced background hiss on FM and an almost total lack of noise - as well as increased fidelity - on AM. Detractors say the sound is "harsh," and that even if it sounded good, the well-documented interference to the analog signal just isn't worth it.
Where both sides agree, however, is in coverage area: Due to digital signals being limited to just one one-hundredth of the analog power, HD Radio coverage can be far less than analog. In some cases, you need to be within a few miles of the transmitter to pick up HD.
In response, the National Association of Broadcasters is lobbying the FCC to allow stations to increase digital power to one-tenth of the analog signal.
What would that do to regular radios?Answering the question is the Corporation for Public Broadcasting, through its NPR Labs, which just released the results of an 18-month study of the effects of increased digital signals to the FM band.
Among the highlights:
At the current 1 percent power level, digital coverage with car radios is typically 85 percent of the normal analog coverage. However, for home and portable radios with smaller antennas, digital only hits 38 percent of analog's coverage area. If the digital power is increased to 10 percent, however, car radio coverage actually is better than analog, at 117 percent. For home and portable use, it increases to slightly more than 80 percent.
While interference to analog radios from digital broadcasts is barely - if at all - noticed by listeners now, increasing the power of digital broadcasts would cause substantial interference, decreasing analog coverage areas as much as 50 percent. Stations you once heard may just disappear on your old radio.
What does this do for the NAB's lobbying effort? Probably not much. My guess is you'll see limited authorizations for higher digital power levels anyway, since the NPR Labs study didn't actually measure interference but rather used computer models to predict it. And while NPR Labs is highly respected, until real-life tests confirm the findings, it is all just a guess.
Copyright © 2008 Richard Wagoner and Los Angeles Newspaper Group.
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