Utility Encounters Mixed Success in Avoiding Amateur Spectrum with BPL:

Amateurs in the Raleigh, North Carolina, area say electric utility Progress Energy and Broadband over Power Line (BPL) equipment provider Amperion have had "some success" in their efforts to avoid using Amateur Radio spectrum on overhead lines in their BPL field trial areas. But problems persist, and the process is far from quick and simple, says ARRL North Carolina PIO Gary Pearce, KN4AQ, who has been among local amateurs closely monitoring the Progress Energy/Amperion BPL trial. Their experiences could indicate what amateurs may face in areas where BPL is widely deployed.

"The mitigation process at this iteration of Amperion's hardware is neither simple nor precise," Pearce said earlier this month. Progress Energy/Amperion essentially are attempting to "notch out" or completely avoid ham radio frequencies, since hams have been the only HF users so far to file interference complaints. Complicating the effort, he says, is that the process is largely hit or miss, requiring field monitoring and feedback and sometimes another attempt to nail the target.

Pearce says he and Wake County ARES Emergency Coordinator Tom Brown, N4TAB--an engineer with extensive RF experience--met the week of April 5 with Progress Energy network engineer Bill Godwin at the so-called Phase II BPL trial areas to review the BPL spectrum in use. Amateurs also monitored the system using an Amateur Radio mobile station some 75 feet from the line.

"Bill Godwin had a chart showing where BPL could operate and avoid ham bands, and Amperion had adjusted its system to comply with that chart," Pearce said. Among other issues, Amperion missed the mark on 20 meters--starting a BPL signal block on 14.300 MHz instead of 14.350 MHz, he pointed out.

Pearce attributed the problem to a likely error in calculating the spectrum needed. BPL spectrum block edges "are not brick walls," he said, but taper off, with progressively weaker carriers remaining audible up to 100 kHz away, depending on the noise floor. "The remaining signals are very weak but would bother a home station within a city block or two of the power line." The goal is to be able to place BPL on a line in the immediate vicinity of a ham.

Unclear at this stage is whether the "notching" scheme will work in a more-dense BPL environment. "More spectrum can be used below 7 and above 30 MHz, but Amperion prefers to remain between 7 and 30 MHz," Pearce said. "If this spectrum can be rotated between line segments, and the notches can be deepened some, they may satisfy the concerns of hams for the Amateur Radio spectrum." But, he adds, no efforts are under way to avoid other shortwave frequencies.

"We appreciate this proactive attempt," Pearce said. "We will point out again that there are other public uses and users of the spectrum in between the ham bands." Amateur Radio operators "cannot sit back and say, 'Well, our problem's solved. Good luck with yours!'" Pearce says.

He says that for this reason alone, the North Carolina amateurs still consider BPL a flawed concept. And, while he credits Progress Energy and Amperion with cooperating to resolve amateur interference issues piecemeal, "we just want to make sure that everyone understands where the goal line stands."

Source:

The ARRL Letter Vol. 23, No. 16 April 16, 2004

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