| 摘要 |
<p>RATE CODE DECODING SYSTEM In railway signaling systems which transmit rate code signals along track circuits, which signals are picked up by the trains and used for signaling purposes, such as speed control, the rate code signals of the same repetition rate received when the train passes between adjacent track section may suffer a phase shift, also known as a phase jump. To prevent loss of the rate code signal during a phase jump, an improved rate code decoding system is provided wherein a correlation process is applied to the received rate code signal by multiplying the signal in separate multipliers with reference signals which are in quadrature and then cross-correlating the output of the multipliers with a step function and summing the absolute values of the outputs of the cross-correlators to provide a level which is substantially constant in the presence of a phase jump. The cross-correlation system provides a filter with a response which is effectively rectified by removing the notch which otherwise would result in the presence of a phase jump. The system may include means for decreasing the time required for the system to acquire the rate code signal when it first appears and in the presence of multiple phase jumps which occur in rapid succession. The system is especially suitable for use in railroads having short track circuits subject to phase jumps in the received rate code signals, for example, when the train travels along the tracks at high speeds.</p> |
