| 摘要 |
<p>A modulation system for railway track circuits in which a modulated signal is applied to a section of track for the purpose of detecting the presence or absence of a train on the section. Such circuits are used to control signalling and they are vital to safe operation of a railway. At a transmitter end, the output (19) of a power amplifier (18) is connected to a section of track. The power amplifier (18) receives the modulated signal from a modulator (17) which is itself controlled by a pseudorandom binary sequence generator comprising a clock (11), a shift register (10), and a modulo 2 adding circuit (13, 14, 15). Equivalent circuitry is used at a receiver end to recognize the pseudorandom sequence in the absence of a train on a given section of track. The likelihood of interference from a train on that section generating an interference signal capable of being mistakenly recognized for the absence of a train can be reduced to an arbitrarily low value.</p> |
