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Device for increasing the safety with respect to transmission faults in an information transmission system

  • US 4,121,208 A
  • Filed: 03/11/1977
  • Issued: 10/17/1978
  • Est. Priority Date: 03/26/1976
  • Status: Expired due to Term
First Claim
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1. In a device for increasing security with respect to transmission faults in an information-transmission system, particularly for the railroad field, in which an interrogation device and a passive response device are movable relative to one another;

  • the interrogation device transmitting an interrogation signal, which can be periodically swept through a predetermined frequency band, preferably in the microwave range;

    the interrogation device receiving, during a read operation of at least two periods from the passive response device, a frequency-selectively reflected interrogation signal, in accordance with a k-digit information item to be transmitted;

    the combination of means for amplifying such a reflected interrogation signal received by the interrogation device;

    means for monitoring the level of the low-frequency portions of such a reflected interrogation signal lying below the sweep frequency of the interrogation device and for reducing the amplification of said amplifying means if the level of such low frequency portions reaches a predetermined threshold value, whereby such low frequency portions do not undesirably exceed such threshold value;

    switch means for controlling the through-connection of the response signal to subsequent devices; and

    control means connecting said monitoring and switch means, for controlling the latter to prevent passage of a transmitted information item in the presence of a decreasing and/or increasing level of such low frequency portion.

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