Power line telecommunications (PLT) is a technology that uses electrical power lines for the distribution of high data rate telecommunication services. There are two main types of PLT systems: access PLT that covers the “last mile” between the electricity supply sub-station and the user; and indoor PLT which aims to distribute data (coming for example from access PLT or DSL) within building via the electricity sockets.
PLT below 80 MHz: no radiation limits
Initially PLT systems operated in the frequency bands below 30 MHz, therefore resulting in potential interference to radiocommunication services in the LF (Low-Frequency), MF (Medium-Frequency) and HF (High-Frequency), where AM radio is received. Since several years, different standardization bodies (CENELEC, CISPR, ETSI) have been dealing with radiation limits for PLT systems. PLT manufacturers have been very active to avoid radiation limits that might be constraining on their systems. On the other side, broadcasters have been working to set limits which would adequately protect licensed broadcasting services from co-channel interference.
At the ITU level, the attempts to approve recommendations limiting this type of radiations in the radiocommunication sector, have so far been unsuccessful. Whilst work is ongoing in all these standardization bodies, the current lack of standard for radiation limits applicable to PLT means that there are no constraints on PLT equipments with regard to the protection of licensed broadcasting.
PLT up to 300 MHz: potential interference to FM and T-DAB services
Developments in PLT technology have made possible for PLT systems to operate up to 300 MHz thus overlapping with the broadcasting Bands II (87.5-108 MHz) and III (174-230 MHz) where main stream FM and DAB radio services are located. The standardization sector of the ITU, the ITU-T, has approved a recommendation specifying these high speed PLT systems for home networking which, in the broadcaster’s views, does not take into account adequate protection of broadcasting services. Preliminary tests of one, commercially available, PLT device are very worrying for broadcasters (see https://www.youtube.com/watch?v=z3yVu5IfaEY). Coordination between broadcasters is ongoing in order to undertake tests and define common positions on this issue in the relevant standardization forums.