Development of a train detection system and a spread spectrum transmission system for track circuit

Train safety is secured by signalling system. The signal is transmitted to the train via mil track circuit. This transmission system is influenced by train traction current in the rail. So that, track circuit transmission system of Shinkansen, the high speed train which operates 275km/h normally and maximum record is 440km/h, adopts SSB signal, which is synchronized with power supply frequency, to avoid the influence of the harmonic waves. This excellent system is operated over 33 years without a fatal accident. Nevertheless the environment of the track circuit had become more worse. Then Central Japan Railway had begun basic experiments of narrow band SS (Spread Spectrum) system which can endure heavy noise environment. The experiments had succeeded and the theory and results are described in this paper.