Locating system

  • US 5,144,312 A
  • Filed: 07/09/1990
  • Issued: 09/01/1992
  • Est. Priority Date: 07/22/1989
  • Status: Expired due to Fees
First Claim
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1. A system for locating a transponder within a defined area, the system comprising a base station and two spaced-apart slave stations at known locations, the transponder and at least those slave stations remote from the base station each incorporating a means to receive signals transmitted from the base stations, an electronic flywheel circuit, and a means to bring the flywheel circuit into synchronism with the received signal from the base station, the signal from the base station being modulated at the frequency of the flywheel circuitry, the transponder also incorporating means to transmit a radio signal modulated at the frequency of the flywheel circuit at a predetermined time interval after receipt of the said signal from the base station, said time interval being set by reference to the flywheel circuit of the transponder, and each slave station incorporating means to receive the radio signal from the transponder and to determine by reference to the flywheel circuit of the respective slave station the time of receipt thereof, the system also including means to determine from the known locations of the base station and the two slave stations and from the times of receipt of the radio signal from the transponder the location of the transponder.

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