FCC commissioners need to do a better job of justifying the agency's rules governing broadband-over-power-line emission levels, according to a federal appeals court.

In a ruling last month, the U.S. Court of Appeals for the D.C. Circuit ruled in favor of the amateur-radio organization ARRL on two items regarding the FCC's BPL rules, requiring the agency to disclose the entirety of its BPL field tests cited in the rules and to explain its reasoning for emission-level limits.

David Sumner, CEO of ARRL, said the court's decision to have the FCC revisit the emission-level rules was particularly significant.

“It's very unusual for the court of appeals not to defer to the expert agency on a technical issue like the [emission-level] extrapolation,” Sumner said. “In an appeal of this kind, most of the time the court upholds the agency, so we're certainly delighted the court found the evidence of prejudice by the commission in the record.”

The court ruled in favor of the FCC on the ARRL's contention that the BPL rules would allow harmful interference to mobile amateur-radio operations. However, the FCC rule that extrapolates that emission levels below 30 MHz decay at 40 dB per decade — a figure that is accurate for a single-point emission source but not for a power line, Sumner said — was not supported adequately in the agency's record, the court ruled.

The FCC can appeal the ruling to the full circuit court or to the Supreme Court. If it declines to appeal, the agency must revisit the emission-level extrapolation issue, either providing reasoned justification for the 40 dB-per-decade factor or establish a new extrapolation factor.

If the FCC were to use the 20 dB extrapolation factor advocated by ARRL, it likely would affect the economics to deploy the technology, Sumner said.

“Presumably, the power would have to be turned down in these systems, and that might result in reduced reliability, reduced throughput and the need for more hardware to be installed — repeaters at closer intervals along the line,” Sumner said. “So we anticipate that the industry is going to strongly resist a revised extrapolation factor.”