| 摘要 |
<p>1481494 Track apparatus STANDARD TELEPHONES & CABLES Ltd 8 April 1975 14319/75 Heading B7N [Also in Division H4] In the train position indicating system in which low power radar is used to interrogate simple transponders moving relative to the radar as described in Specification 1,479,616 inductive coupling means is provided between the radar and each transponder so that each transducer is enabled to provide a response only when the radar is close enough thereto to trigger inductively the transponder. As described, the radar device 1 mounted on a train includes an inductive coupling loop 12 located adjacent antenna 11, and driven by a 100 kHz signal from oscillator 13. The track mounted transponder 2 comprises an inductive track loop 22 adjacent its antenna 21. Mutual coupling between loops occurs only when train antenna 11 is substantially above antenna 21 so that spurious responses from nearby transponders are avoided. Track loop 22 is coupled to RC tuned rectifying network 23, 24, 25 which provides a D.C. output signal when mutual coupling between loops 12 and 22 occurs. Transponder 20 input comprises a switching means (not shown), e.g. a F.E.T., which is responsive to the D.C. signal 26, the presence of which enables the transponder. The presence of inductive coupling and therefore of a transponder can be detected in oscillator 13 on the train and may be used to trigger an alarm on lack of detection of the associated response signal received by radar 10 from the same transponder.</p> |
