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No Power to the People
Does Low-Power FM Radio Cause Unacceptable Interference?
By Mariama Orange
November 2001
In January 2000 the Federal Communications Commission, under the administration of then chairman William Kennard, authorized the creation of an exclusively noncommercial low-power FM (LPFM) radio service. By squeezing between existing stations in the FM band, low-power stations would provide local access and diversity to airwaves now dominated by media conglomerates.
SEPARATION ANXIETYThe mandatory spacing scheme for FM radio was adopted in 1963, when radios were primarily analog and tuned by turning a knob. "The spacing requirements never changed" to reflect current technology, explains Bruce A. Franca, acting chief of the FCC's Office of Engineering and Technology. An August 1999 study conducted by Wireless Valley Communications, an engineering firm based in Blacksburg, Va., found that modern FM receivers, which use digital frequency synthesis and phase-lock loop detection, can tolerate much closer adjacent channel spacings than FCC rules allow. |
That vision, though, has been clouded by LPFM opponents--largely those who already have a license to broadcast. They argue that the new stations would make the already snug FM band too close for comfort, producing unacceptable levels of interference. Their claims have already led the FCC to tighten the specifications on its original LPFM proposal and pushed Congress to pass legislation that severely curtails the number of eligible LPFM slots by 75 to 80 percent. Yet Congress may be reacting more to political pressure than technical data, which suggest that whatever interference LPFM stations generate will be too low to matter.
Today's FM stations operate in 200-kilohertz-wide channels, transmitting at center frequencies that range from 88.1 to 107.9 megahertz. The closer in frequency that two stations broadcast, the farther away they must be from each other geographically to prevent interference. The FCC prescribes minimum-distance separation rules for stations whose center frequencies are three channels (600 kilohertz) apart or fewer.
Because LPFM stations transmit only at 10 or 100 watts, reaching out no more than 3.5 miles, the FCC originally decided to waive the 600-kilohertz separation reqirements for them. (Full-power stations pump out 6,000 to 100,000 watts, covering an area in an 18- to 60-mile radius.) Congress's action, however, effectively enforces the 600-kilohertz separation requirements, leaving no spectrum for a significant number of the originally planned LPFM stations. That's exactly the point, according to LPFM opponents, which include the National Association of Broadcasters (NAB), National Public Radio and the Consumer Electronics Association. "It is impossible to shoehorn the number of stations [the FCC had wanted] without significant interference for listeners," states Dennis Wharton, NAB senior vice president of communications.
But three-channel-wide protection isn't necessary for LPFM, argue advocates that include the Media Access Project (MAP), the National Lawyers Guild's Committee for Democratic Communications and the Prometheus Radio Project. Technical studies conducted by the FCC's own engineers conclude that relaxing the 600-kilohertz rule for LPFM would not result in much new interference for existing stations. In addition, one of the major purposes of authorizing LPFM stations was to fit them into buffer zones too small to accommodate full-power stations, thereby maximizing spectrum efficiency.
The LPFM debate has prompted key questions about how to determine what levels of interference actually cause problems. Wharton disagrees with those who describe LPFM as producing "acceptable levels of interference," dismissing their conclusion for inappropriately using a creative phrase. Similarly, LPFM proponents have discounted an NAB technical study submitted to the FCC for inappropriately using creative testing procedures. The NAB study found that receivers would not be able to stand up to interference produced by relaxing the 600-kilohertz rule for LPFM; however, MAP counters, the same study used an arbitrary performance threshold so extraordinarily high that most of the receivers failed to measure up even when there was no interference present.
In February, Senator John McCain of Arizona introduced the Low Power Radio Act of 2001, which would essentially reverse Congress's decision to curtail LPFM. That bill still awaits action. Meanwhile, starting this past April, the FCC has slowly begun doling out the first LPFM construction permits, barely squeezing out a taste of the airwaves to appease the flood of communities starving for a voice. Mariama Orange is an electrical engineer from Howard University.
