UK Regulator's Study Points Up Limitations of Amperion-Equipped BPL Trial:

Ofcom, the UK's telecommunications regulatory agency, has concluded that Amperion BPL equipment deployed in a field trial in Scotland "as tested is not and cannot be FCC Part 15 compliant above 30 MHz." Ofcom this week released a study, "Amperion PLT Measurements in Crieff," which summarizes measurements it took at the site. PLT is another term for BPL. Ofcom's investigation also demonstrated the limitations of Amperion's "notching" capabilities to mitigate interference to radio reception. ARRL CEO David Sumner, K1ZZ, says Ofcom's study reflects what the League and others have known all along about BPL.

"Ofcom's measurements and conclusions are consistent with ours and with what we have been saying all along about BPL in general and Amperion in particular," Sumner said. "It's a shame that we have to look overseas to find a regulator who will say what truly needs to be said: Medium voltage power lines are no place for HF broadband data."

Measurements were made at the pilot system in Crieff, which uses 11 kV overhead power lines and Amperion Griffin PLT equipment made in the US and employing OFDM signal architecture. The Ofcom study says that at HF, radiated leakage emissions from the Amperion-based BPL network operating at its maximum power setting exceeded FCC Part 15 limits by up to 8 dB.

The UK has no defined PLT emission limits, and Ofcom used the FCC's as a reference point. The Ofcom investigation also concluded that if Europe adopts Reg TP NB30 radiated emission limits now in effect in Germany, "such adoption would rule out any European deployment" of the Amperion Griffin BPL equipment on which it took measurements in Scotland.

Above 30 MHz, Ofcom said, radiated leakage exceeded FCC Part 15 limits by up to 27 dB. "In practice, the launch power would need to be reduced by 27 dB to ensure compliance with the FCC limit, and this raises two issues," Ofcom said. "The first is that such a reduction is beyond the 24 dB power control range of the product and secondly it seems certain that the network would fail to provide any functionality at such a reduced power level."

The notching facility of the equipment as an interference mitigation technique "is compromised," Ofcom concluded, "because notches cannot be placed in the 'upstream' spectrum, and because FCC Part 15 limits are too relaxed to permit the notched spectrum to afford any significant protection to weak signal reception."

A 20 dB notch "is not an effective interference mitigation measure for weak signal reception that is limited only by the local spectrum noise floor," Ofcom said in its report. It concluded that at that level of notching, "Part 15 compliant leakage emissions from a notched PLT line would contribute noise to the HF spectrum at distances as far as 1 km [approximately 0.62 mile] from the line."

Beyond that, Ofcom said, Amperion encountered difficulties when requested to implement a 30 dB notch from 21 to 22 MHz to cover both the amateur 15-meter band and the adjacent HF broadcast band. "They reported problems with this, due to the bandwidth required," the report noted. Graphs indicate that the notching "uncovered" several broadcast signals, most with field strengths in excess of the ITU-recommended minimum protected value.

In its report, Ofcom noted that power lines were not designed, shielded or balanced for high-frequency use and can radiate significant leakage even when buried below ground. "PLT leakage emissions occupy parts of the high frequency radio spectrum above 2 MHz and have the potential to interfere with the reception of radio communication services, including shortwave broadcasts," the agency said.

While the BPL/PLT interference issue has "proved to be contentious" and continues to be a discussion topic in Europe and elsewhere, Ofcom said, it also appears that "none of the proposed emission limits can currently satisfy the dual objective of protecting radio reception whilst, at the same time, allowing PLT to operate in a commercially viable manner."

The Ofcom study involved a BPL field trial by Scottish and Southern Energy plc (SSE). The agency says it believes its measurements were "sufficient to indicate the general situation" at the Crieff site. A copy of the Ofcom report is on the ARRL Web site http://www.arrl.org/tis/info/HTML/plc/files/amperion.pdf.

According to the Radio Society of Great Britain, an SSE representative indicated recently that the company would not be undertaking any further PLT rollout in the UK and was unlikely to invest further in the technology. Reasons given were the lack of progress on PLT technical standards and the commercial position of PLT with respect to other broadband services. The RSGB said it welcomed the announcement.

Source:

The ARRL Letter Vol. 24, No. 19 May 13, 2005

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