A standard technique is already available for measuring radio noise emitted to the outside by railway systems, and an international standard has also been established. However, no suitable measuring instrument is available for internal radio noise, and no measuring method has been established.

Fig.1 Highly sensitive triaxial photoelectric sensor

      In response to recent drive system developments, the introduction of IT technology and demand for electromagnetic environment standardization, it has become increasingly necessary to establish a method of measuring internal radio noise. An application method was therefore developed to measure such noise using a small, wide-band photoelectric sensor (Fig.1). Its suitability as an on-board measuring instrument was ensured by making it highly sensitive and triaxial (vertical + two horizontal directions).

      Trial measurements were carried out on commuter and special express trains by combining the highly sensitive triaxial photoelectric sensor with a measuring instrument that can conduct frequency analysis in real time. The results showed that hourly variations in the frequency characteristics of on-board radio noise could be measured and the emission direction could also be captured (Fig.2). By measuring these characteristics and understanding their intensity distribution, effective measures to clean up the on-board electromagnetic environment can be planned and implemented. The results of this study will be used not only as an internal standard for measuring on-board radio noise, but also as a foundation for Japanese representation in international standardization committee deliberations regarding on-board radio noise.

      This study was sponsored by the Ministry of Land, Infrastructure and Transport.

Fig.2 Time variations in the frequency characteristics of radio noise on board the inverter-controlled vehicle