NTIA Study Documents Radio Interference from BPL:

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. 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 added, "technical rules governing their deployment must address potential harmful interference to critical systems." Released April 27, NTIA Report 04-413 http://www.ntia.doc.gov/ntiahome/fccfilings/2004/bpl/index.html analyzes 10 million BPL system measurements.

"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, the agency said, "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 it 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.

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.

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.

Source:

The ARRL Letter Vol. 23, No. 18 April 30, 2004

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