| 摘要 |
An improved audio frequency track circuit system utilizes a synchronous train detection arrangement and reduces the number of fixed code rate modulated carrier signals. As few as two carrier signals are alternately applied at discrete points along a pair of jointless track rails to define the transmitter ends of the track sections, with complementary receivers defining the opposite ends. The two carrier signals are coded at one of two phase angles which are 90 DEG out-of-phase so that, when assigned, the nearest possible interfering signal is 90 DEG out-of-phase and is rejected thereby. Like carrier frequency transmitter/receiver arrangements are disposed on opposite sides of an insulated joint but are coded 180 DEG out-of-phase so that a breakdown of the insulated joint is detected and the false code signal is rejected.
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