NTIA Study Shows BPL Interference Potential
May 4, 2004
The NTIA released Phase 1 of its analysis of interference from broadband access over power line (BPL) technology. Although NTIA concluded, "Critical review of the assumptions underlying these analyses revealed that the application of existing Part 15 compliance measurement procedures for BPL systems results in a significant underestimation of peak field strength," it stops short of recommending BPL be abandoned as others have proposed. The NTIA report lists several steps BPL providers should take to reduce interference to other users of the spectrum from 1.7 to 80 MHz (which includes TV channels 2, 3, 4 and 5 as well as all the shortwave broadcasting bands), including differential-mode signal injection, absorbing filters, adopting a "one active device per frequency and area" rules and using a single point of control for each BPL service area.
It also references the experiences other countries have had with BPL. Austria has terminated pilot power line communication (PLC) projects after concluding the interference caused by PLC to communications in the frequency range 2-30 MHz could not be reduced to acceptable levels. Finland decided PLC technology can be accommodated only after interference and security problems have been solved and when the technology complies with official requirements. It favors compliance with the NB30 standard until a pan-European norm is specified. Germany has adopted the NB30 standard. Japan determined that at this stage increasing the bandwidth used for power line communications would be difficult. Figure 3-1 in Volume 1 of the report compares the Part 15 limits requested by BPL proponents in the U.S. with the German NB30 standard and the proposed Norwegian, BBC and NATO standards. The NB30 limits above 15 MHz are over 40 dB stricter than those requested by the BPL proponents. The BBC and NATO proposals are even stricter, with allowed emissions 70 dB less than those requested by the BPL proponents over the entire HF spectrum. NTIA found the potential for interference from BPL systems exists over 500 meters from the system at 15 MHz and at some locations 700 meters away at 25 MHz. The report said, "Results showed that aggregate interference levels to the aircraft could exceed average ambient RF noise levels at two frequencies (15 MHz and 25 MHz), at distances ranging from thirty-three kilometers (six kilometers altitude) to over 50 kilometers (altitudes between six and twelve kilometers)." For a summary of the NTIA study, see the ARRL news story NTIA Study Documents Radio Interference from BPL. The complete NTIA study is quite large but contains useful information on how BPL works as well as a large amount of calculated and measured data on interference from BPL systems. While no frequencies above 50 MHz were studied, the report notes that some BPL systems could use frequencies as high as 130 MHz, which would include aeronautical radio navigation frequencies and the FM broadcast band. See the index to the BPL Phase 1 Report (NTIA Report 04-413) for information on downloading the document. Phase 2 of the report will "evaluate potential interference from mature deployments of BPL systems via ionospheric signal propagation and further assess risks of local interference under various candidate BPL rules, including rules suggested in NTIA's Phase 1 study."
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