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FCC Looks at BPL Interference

Last Monday the FCC released the text of the Notice of Proposed Rule Making (NPRM) on Access Broadband Over Power Line Systems (BPL). In the NPRM, the FCC disagreed with the American Radio Relay League (the ARRL, representing Amateur Radio operators) and others that suggested Access BPL systems complying with Part 15 lines would could widespread interference to communications.

The NPRM said the FCC believes that "the primary source of emissions will be individual couplers, repeaters and other devices and, to a lesser extent, the power line immediately adjacent thereto." The NPRM continues, "In general, we believe that a properly designed and operated BPL system will pose little interference hazard to non-amateur services such as aeronautical, maritime and public safety. However, it is foreseeable that under certain rare circumstances a public safety unit could:(a) operate in close proximity to an Access BPL device; (b) be tuned to a frequency radiated by the Access BPL device; and (c) be receiving a weak signal from a distant, or obstructed, public safety base station. In general, potential harmful interference under these conditions would be limited to public safety units operating on systems using low-band VHF channels (25-50 MHz)."

The NRPM did not address interference to TV Channel 2, which starts at 54 MHz and unlike the public safety radio systems, uses VSB AM modulation (for video) which is much more susceptible to noise than the FM modulation used by public safety radio systems. Regarding amateur radio operations, the NPRM said, "While we agree that there is some potential for Access BPL to cause harmful interference to radio services, we also tentatively conclude that the likelihood of such harmful interference is low under the current limits and that where such interference does occur, there are remedies that the Access BPL operator can employ to eliminate such interference."

The story FCC Proposes Rules for BPL Systems on the ARRL Web site describes what ARRL CEO David Sumner, K1ZZ sees as the problem. "While Part 15's current limits on unintentional radiators on HF may be appropriate for short-duration, narrowband emissions, they are inappropriate for the sort of long-duration, broadband emissions BPL would employ." Sumner compared the short-duration, narrowband emissions at the Part 15 radiated emission limit to a helicopter flying overhead. "The noise is deafening, but is tolerable because it doesn't happen very often nor last very long. To a radio user, having BPL in the neighborhood would be like having the helicopter hovering constantly overhead."

The proposed rules for dealing with interference from Access BPL were described in Feb. 16 RF Report. The NPRM provided little new data on how shortwave radio listeners would be protected, although it did include comments from the North American Shortwave Association and from Aeronautical Radio Inc. expressing concerns about interference in the HF spectrum. It also mentioned comments from Verizon Telephone Companies, Qwest Communications International, Inc. and Spring Corporation expressing concern that "BPL operations could interfere with voice and data services (i.e. VDSL and ADSL2+) on twisted pair telephone cables located on the same utility poles as the BPL systems."

The NPRM asked for comments on a proposed procedure for measurements to ensure radiated emission limits do not exceed the Part 15 limits. "We tentatively propose that Access BPL systems, including all BPL electronic devices, e.g., couplers, injectors, extractors, repeaters, boosters, concentrators installed on the electric utility overhead or underground medium voltage lines etc., be measured in-situ to demonstrate compliance with our Part 15 rules, at a minimum of three overhead and three underground representative locations, using the measurement guidelines in Appendix C. Consistent with existing FCC measurement procedures, measurements below 30 MHz must be performed with a magnetic loop antenna, while those above 30 MHz are performed using an electric field sensing antenna. For Access BPL in underground installations, the proposed guidelines employ the common principle of measuring radiated fields along a number of radials at a specified distance from the periphery of the pad-mounted above-ground transformer where the Access BPL equipment is located, to find the maximum emissions. For Access BPL installed on overhead lines, in order to take into account the effect of the long power line associated with the Access BPL equipment, our proposed guidelines specify measurements at fixed horizontal distances from the power line where the Access BPL source is installed. Thus, rather than finding the maximum emissions across a number of radials, -- as currently performed for other Part 15 emitters -- the receive antenna is moved down-line, parallel to the power line, starting from the Access BPL equipment location, to find the maximum emissions. Down-line distances used in this sequence of measurements are specified in terms of wavelength of the Access BPL mid-band frequency."

The FCC asked for comments on whether the proposed fixed antenna height of one meter for loop antenna measurements and scanning heights from one meter to four meters for electric field sensing antennas were appropriate. Should antenna heights greater than those proposed in Appendix C be used? Is it "safe and practical to [make] the in-situ emission measurements at heights up to the height on an overhead medium voltage power line (typically 11 meters) when operation 10 meters from the power line?" Alternatively, should the FCC specify a correction factor for measurements "performed at heights significantly lower than the power line" to estimate the maximum field strength at a higher measurement height?

The proposed FCC rules exempt Access BPL from the conducted emission limits of Section 15.107(c). The NPRM asks whether Access BPL would, in some cases, operate in the AM broadcast band and whether "specific conducted requirements are needed in such situations."

The impact of Access BPL on low-band VHF (Channels 2-6) and FM broadcast reception was not mentioned anywhere in the NPRM, even though some BPL systems can generate signals in this range and those that don't could have harmonic radiation falling in these bands. The NPRM mentions that Satius, Inc filed comments proposing higher emission limits, especially at frequencies above 200 MHz. Would BPL operations in this range interfere with high-band VHF TV (Channels 7-13) reception?

Reading through the NPRM, the FCC and proponents of Access BPL have a much different opinion of the impact of the technology on high frequency and low VHF communications than many of the users of that spectrum. Both the ARRL and NTIA should be reporting on the results of their testing soon. The deadline for comments on the NPRM will be 45 days from the publication in the Federal Register. Reply comments are due 75 days from publication in the Federal Register.

The debate on interference from Access BPL is likely to continue even after the comment dates pass. Will Access BPL providers be able to avoid using frequencies that would interfere with TV and shortwave radio listening and with amateur radio communications? If there is interference, how will the Access BPL providers react and will the FCC intervene if necessary? Look for additional stories on this topic in future editions of RF Report.