| 摘要 |
An audio frequency track circuit with improved security in the train detection function for rapid transit applications for use with uninsulated rails includes an improved transmitter and receiver. The transmitter modulates a track frequency carrier with a fixed code rate, regardless of the code rate employed to modulate the train information frequency. The receiver includes a decoder tuned to the track frequency modulation rate. By using such a sharply tuned decoder, the noise protection threshold is increased. Because of its application to uninsulated rails, with the associated lack of hard track circuit boundaries, adjacent track circuits have different track frequency modulation rates to insure that the modulated track frequency signal, from one track circuit, is not effective to operate a track relay in another circuit even under failure conditions.
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