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 Previous: Card Checking for Japan Amateur Radio League (JARL) Awards at Dayton | ![Next (later) Story](/images/sty-up.gif "Array of "ARRL Stage" Presentations Among ARRL EXPO 2005 Highlights"){kind=small} Next: Array of "ARRL Stage" Presentations Among ARRL EXPO 2005 Highlights |
NEWINGTON, CT, May 11, 2005--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 today released a study, "Amperion PLT Measurements in Crieff," which summarizes measurements it took at the site in Scotland. 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."
 An Ofcom graph showing how a notch "uncovered" several AM shortwave broadcast stations that were otherwise inaudible. |
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."
 Amperion pole-mounted BPL equipment in the now-decommissioned Cedar Rapids, Iowa, field trial. The 2.4 GHz Wi-Fi link antenna is visible. [Alan Erickson, WB0OAV, Photo] |
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, and subsequently the 20 dB notch was provided for the 21.45 to 21.9 MHz broadcast band," the report noted. Graphs indicate that the notching "uncovered" several broadcast signals. Most of the signals revealed had field strengths in excess of the ITU-recommended minimum protected value, Ofcom indicated.
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 . The agency says it believes its measurements were "sufficient to indicate the general situation" at the Crieff site.
Two earlier Ofcom reports, "Ascom PLT Measurements in Winchester," and "DS2 PLT Measurements in Crieff," are available via the Ofcom Web site. Additional information about BPL and Amateur Radio is on the ARRL Web site's Broadband Over Power Line (BPL) and Amateur Radio pages. To support the League's efforts in this area, visit the ARRL's secure BPL Web site.
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