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 Previous: Confessions of a QSL Card-aholic |  Next: The K7RA Solar Update |
 BPL applies radio frequency energy to low and medium-voltage power lines to provide broadband access to homes and businesses. |
NEWINGTON, CT, Apr 29, 2004--The first phase of a long-awaited broadband over power line (BPL) study the National Telecommunications and Information Administration (NTIA) released this week suggests it's possible to accommodate BPL technology while managing the interference risk. Now part of the US Department of Commerce, the NTIA manages spectrum allocated to federal government users and advises the White House on telecommunications issues. In a cover letter to FCC Chairman Michael K. Powell, Acting NTIA Administrator Michael D. Gallagher pledged that the NTIA would "work with the Commission to establish a firm technical foundation for responsible deployment of BPL to protect critical federal communications systems." But, Gallagher said, while BPL systems may present a valuable economic opportunity, "technical rules governing their deployment must address potential harmful interference to critical systems." Released April 27, NTIA Report 04-413 analyzes 10 million BPL system measurements and "provides a roadmap" to deploying BPL systems while managing interference, Gallagher's letter said.
"Most studies have been oriented to determine whether interference will occur at the variously proposed limits," NTIA says in describing its study's approach. "In contrast, NTIA has oriented its study to find a solution that accommodates BPL systems while appropriately managing the risk of interference to radio systems." The NTIA acknowledges that BPL signals "unintentionally radiate" from power lines, but "there is substantial disagreement as to the strength of the emissions and their potential for causing interference to licensed radio systems. The NTIA also said current FCC Part 15 measurement techniques may "significantly underestimate" peak BPL field strength.
The hefty, two-volume NTIA Phase 1 study looks at BPL systems using the HF and low-VHF spectrum from 1.7 to 80 MHz and "defines risks of interference from BPL systems to local radio reception" while assuming the systems comply with existing Part 15 rules. That spectrum, NTIA said, is home to some 59,000 federal frequency assignments. The study proposes protecting 41 frequencies of the "most sensitive and likely most severely affected federal systems."
ARRL CEO David Sumner, K1ZZ, said the NTIA study clearly demonstrates that BPL systems pollute the radio spectrum. "How can any responsible public official encourage the deployment of such systems," he asked, "and how can any investor seriously consider pouring money into such an obviously flawed technology?"
Among interference mitigation techniques, the NTIA study recommends reducing BPL device output power--which the study called "the single most effective method" of reducing interference potential--and "shifting or notching" BPL frequencies. Others included differential-mode signal injection, absorbing filters, adopting a "one active device per frequency and area" rule and using a single point of control for each BPL service area.
The NTIA said it conducted measurements at three different BPL field trial sites to characterize the BPL fundamental emissions. "As the measurement antenna was moved away from the BPL energized powerline," the study said, "The radiated power decreased with increasing distance." But it noted that the decay was not always predictable, with peaks occurring at several locations.
"At one measurement location where a large number of BPL devices were deployed on multiple three-phase and single-phase MV (medium-voltage) power lines," the study continued, "appreciable BPL signal levels (ie, at least 5 dB higher than ambient noise) were observed beyond 500 meters from the nearest BPL-energized power lines." The NTIA said its measurements show that radiated power from BPL-energized lines was consistently higher when the measurement antenna was at a greater height--10 meters as opposed to 2 meters. "These results indicated a need to refine the Part 15 compliance measurement guidelines to ensure that the peak field strength of any unintentional BPL emissions is measured," the NTIA concluded.
Interference calculations by the NTIA engineers indicated that a BPL transmitter operating within Part 15 limits would significantly increase the noise floor for land-mobile receivers on frequencies below 30 MHz. The agency said it could be inferred from its calculations that "a vehicle-mounted HF receiver" operating in a residential neighborhood next to a BPL-energized line "may experience harmful interference" depending on the frequency, distance along the line from the BPL transmitter, the BPL transmitter's duty cycle and the number of BPL devices on the power line.
The NTIA study calculated that interference "is likely" to mobile stations in areas extending to 30 meters and to fixed stations in areas extending to 55 meters from a single BPL device and the power lines to which it's connected. With "low to moderate desired signal levels," the NTIA study continued, interference is likely at these receivers within areas extending to 75 meters for mobiles and 460 meters for fixed stations.
Among other study highlights:
The NTIA study appeared the same day the ARRL appealed to President George W. Bush to withdraw his support for BPL and focus his administration's attention on "more suitable technologies" such as wireless broadband access. In an April 26 speech in Minneapolis, Bush advocated changing technical standards to encourage BPL deployment in the US. ARRL President Jim Haynie, W5JBP, told Bush in a fax that while the League supports universal and affordable broadband access, BPL is the wrong direction to take.
 A BPL medium-voltage "extractor" and box. This one is part of a Progress Energy BPL field trial near Raleigh, North Carolina. [Gary Pearce, KN4AQ, Photo] |
In its BPL Notice of Proposed Rule Making (NPRM) in ET Docket 04-37, the FCC has proposed amending its Part 15 rules to adopt new requirements and measurement guidelines for so-called "Access BPL" systems. The comment deadline is May 3; reply comments are due by June 1.
"Timely and successful completion of the Commission's BPL docket will lay the foundation for meeting the President's vision for the availability of competitive, universal and affordable broadband services by 2007," declared Gallagher's cover letter, which took note of Bush's April 26 remarks. "Responsible technical rules that fully address harmful interference concerns are a vital component of that foundation. In meeting this objective, our agencies must be technically grounded and tenaciously committed to find solutions that both protect critical systems and to allow the realization of a promise of a third broadband wire into the home."
The NTIA says its Phase 2 study will "evaluate the effectiveness" of its Phase 1 recommendations and address potential interference via ionospheric propagation of BPL "from mature, large-scale" deployed BPL networks.
The ARRL Web site provides an information package explaining how members can contact the White House and members of Congress to express their views on BPL deployment and why they need to do so.
For additional information, visit the "Broadband Over Power Line (BPL) and Amateur
Radio" page on the ARRL Web site. To support the League's efforts in this
area, visit the ARRL's secure BPL Web
site.
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