A railroad track fault detector is mounted on a tracked vehicle and uses the track ahead or behind the vehicle as a transmission line for a high frequency signal. The transmission line has a known characteristic impedance in a condition of no track fault. The impedance is included in a bridge network that is excited with the high frequency signal. Bridge imbalance is detected as an indication of a track fault that can be a complete or partial short circuit or open circuit. The bridge excitation is applied to the track through moving contacts like brushes ahead of the front wheels or behind the last wheels. The shunt effect of wheels close to the brushes is eliminated by a tuning impedance that creates an effective infinite impedance to the portion of the track between the moving contacts and the shunting wheels.
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