Interrogator-responder signalling system

Claim 1

AN INTERROGATOR-RESPONDER SIGNALLING SYSTEM COMPRISING AN INTERROGATOR STATION AT A FIXED LOCATION ALONG THE PATH OF A VEHICLE TO BE IDENTIFIED AND A RESPONDER DEVICE MOVABLE WITH THE VEHICLE ALONG THE PATH AND INTO SPACED RELATION WITH THE INTERROGATOR STATION, SAID INTERROGATOR STATION INCLUDING A TRANSMITTER AND IN INDUCTIVE LOOP ASSOCIATED WITH THE TRANSMITTER FOR GENERATING AN INTERROGATOR SIGNAL, SAID RESPONDER DEVICE INCLUDING MEANS FOR DETECTING THE INTERROGATOR SIGNAL AND MEANS FOR GENERATING A CODED RESPONSE SIGNAL IDENTIFIABLE WITH THE VEHICLE, SAID INTERROGATOR STATION INCLUDING A FIRST RECEIVER HAVING A FIRST INDUCTIVE LOOP AND A SECOND RECEIVER HAVING A SECOND INDUCTIVE LOOP, SAID INDUCTIVE LOOPS BEING ARRANGED IN A CONFIGURATION TO DEFINE THREE AREAS, A FIRST OF THE AREAS BEING WITHIN THE FIRST INDUCTIVE LOOP OF THE FIRST RECEIVER AND OUTSIDE OF THE SECOND INDUCTIVE LOOP OF THE SECOND RECEIVER, A SECOND OF THE AREAS BEING WITHIN THE INDUCTIVE LOOP OF BOTH RECEIVERS, AND THE THIRD AREA BEING OUTSIDE THE INDUCTIVE LOOP OF THE FIRST RECEIVER AND WITHIN THE INDUCTIVE LOOP OF THE SECOND RECEIVER, AND A SWITCHING