Broadband access over power lines (BPL) is a technology that couples digitally modulated signals to power lines for distribution to subscribers, using medium wave, short wave and low-band VHF frequencies.
If not engineered correctly, these RF signals can radiate from the power lines and cause interference to radio communications. The American Radio Relay League (ARRL), representing amateur radio operators, took the FCC to court over BPL rules in 2007. The Court agreed with the ARRL on two major points and remanded the rules back to the Commission.
Friday, the FCC released a Request for Further Comment and Further Notice of Proposed Rule Making (FCC 09-60) and placed unredacted staff technical studies into the record of the proceeding. The FCC asked for comment on "the information in these studies as it pertains to our BPL decisions.
One of the concerns expressed by the ARRL was in regard to the selection of a 40 dB per decade extrapolation factor for frequencies below 30 MHz. In the Request for Comment and FNPRM the FCC explained the reasons it used the 40 dB per decade factor and why the technical proposal submitted by the ARRL did not provide "convincing information" that a different extrapolation factor be used. The FCC said more recent studies verify the correctness of its determination.
In the article FCC Continues BPL Debate, ARRL Laboratory and BPL expert Ed Hare, W1RFI, said, "At the same time the FCC released the new FNPRM, it also released 800 MB of previously unseen FCC internal staff reports and videos on BPL."
Hare said that although the FCC had tried to downplay work by its own staff by stating that the reports were the opinion of only a single FCC staffer, FCC Lab conclusions actually reached about BPL came from technical people "with strong experience in measurement techniques and interference assessment."
"This is generally good engineering, with a clear objective of providing the Commission with accurate technical information about BPL." Hare said. "These reports show that BPL causes interference to a number of licensed services for significant distances from BPL noise sources and that the noise from BPL at antennas that are about 100 feet from wires carrying BPL operating at the FCC limits will represent an increase in noise of about 30 dB in most cases."
Why should wireless users be concerned about sharing spectrum with BPL?
Hare explained that the present "rules and test methods--when coupled with inappropriate distance extrapolation--simply do not protect licensed users from interference."
He added that the Commission had been aware of the content of the presentations when the BPL Report and Order discounting the ARRL, when it presented many of the same technical points.
The FCC states the lack of new complaints of BPL interference in the last two years shows the rules are working.
The ARRL observed that in response to its input in the situation, BPL deployment within the U.S. amateur radio spectrum had "essentially stopped."
"The FCC's own video documentation of interference from BPL that is operating under the rules the FCC put forward should be more than sufficient to show that the rules as written are not good ones," the ARRL stated. "The industry has reduced the interference from BPL by doing more than the rules require. By not using the amateur bands and by improving the filtering of BPL systems well beyond the inadequate requirements of the present rules, the industry and ARRL have shown that it is possible to operate BPL systems without widespread interference problems."
While it is unlikely BPL interference will affect DTV reception on high-band VHF channels, and even less likely it will cause problems for UHF DTV reception, it is certainly a concern for amateur radio operators, shortwave listeners and agencies using low-band VHF spectrum for critical communications. As this proceeding advances, I'll post updates in RF Report.
