"Utility companies want to use this new technology to provide value-added services to clients in private homes or industry, such as fast Internet access or relatively fast local-bus systems, simply by plugging anywhere into the 50-Hz, 230-V mains," he explains.

Hansen is chair of a working group for Germany's regulatory agency, RegTP. System measurement data are hard to get from utilities, but he has closely followed field trials in the United Kingdom, Germany, Norway, and Switzerland.

Germany now has regulations (NB 30) that control radiated emissions below 30 MHz in the short-wave user spectrum. These regulations were implemented to protect sensitive military and government monitoring and communication services. Hansen says the results of PLC field trials throughout Europe have shown that injecting such signal levels results in radiated emissions 20–40 dB above Germany's limits.

"Early field trials in the United Kingdom, Germany, and Switzerland showed excessive radiated emissions above NB 30 limits, which are about 20 dB more relaxed than those required in the April 2000 version of the UK's MPT 1570 regulation," he says.

Unshielded low-voltage distribution systems are not designed for communication purposes such as symmetrical subscriber lines (x-DSL). He says that issues such as impedance changes, longitudinal signal attenuation, uncontrolled coupling, light switches, and time-dependent loads present difficulties for evenly distributing RF within buildings. In addition, EMI filters designed for blocking high-frequency PLC signals in IT equipment, TV and video, and appliances also make the use of PLC systems difficult.

PLC technology would certainly provide an attractive alternative to traditional Internet access. However, the technology currently fails to meet the requirements of the EMC Directive. And the few national standards that have been developed do not sufficiently regulate this technology for an international market. More work must be done to address critical issues such as noise floor, signal-to-noise ratio, and the potential interference with existing technologies such as local-area networks and DSL.