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Radionavigation system having means for concealing distance and/or bearing information conveyed thereby

  • US 4,564,840 A
  • Filed: 02/13/1978
  • Issued: 01/14/1986
  • Est. Priority Date: 02/16/1977
  • Status: Expired due to Term
First Claim
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1. In a radionavigation system wherein a ground station includes transmission means responsive to interrogation pulses from passing aircraft for emitting outgoing signals enabling evaluating means aboard said aircraft to derive positional information from the timing thereof,the improvement wherein said ground station comprises error-generating means for introducing an artificial delay into the emission of said outgoing signals to falsify the positional information conveyed thereby, said transmission means receiving from said error-generating means a binary message representing the magnitude of said artificial delay in coded form for communication to on-board equipment of interrogating aircraft, the on-board equipment of privileged aircraft including error-eliminating means for extracting said magnitude from said binary message and controlling said evaluating means to correct the falsified positional information derived from said outgoing signals.

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