Interference Measurements in HF and UHF Bands Caused by Extension of Power Line Communication Bandwidth for Astronomical purpose

摘要

Power line communication (PLC) system which extends the available frequency bandwidth up to 30 MHz has been proposed in Japan. The electromagnetic interference (EMI) problems on PLC had been investigated by the PLC study group organized by the Ministry of Public Management, Home Affaires, Post and Telecommunications (MPHPT). The study group held collaborated field experiments of the PLC facility and we measured interferences caused by the PLC facility in HF and UHF bands in order to evaluate influences of the expansion of PLC bandwidth on radio astronomical observations. In the field experiment, two sets of PLC modems (SS and OFDM) were tested as an access system. During the PLC modems were on, the HF spectra observed showed strong increase of the noise floor level, and it was found that the PLC noise exceeded the level of the galactic noise by more than 30 dB. In UHF band, spurious emission around 327MHz was identified. In both HF and UHF bands, the interferences exceeded the limit of harmful interference level for radio astronomical observation which is given in Recommendation ITU-R RA769-1. Safety distances where the Recommendation was satisfied are estimated to be 219 km and 12 km at 9.2 MHz and 327 MHz, respectively. PLC seems to be a harmful interference source for the radio astronomical observation in both HF and UHF bands.