Code selectors for selective calling systems

Claim 1

A CODE SELECTOR OF THE TYPE USED IN THE RECEIVER OF A SELECTIVE CALLING SYSTEM IN WHICH AN ALARM IS ACTUATED AT A PARTICULAR RECEIVER ONLY WHEN A PARTICULAR BINARY CODE IS RECEIVED AND RECOGNIZED BY THE SELECTOR COMPRISING A RECEIVER LINE UPON WHICH IS IMPRESSED A RECEIVED BINARY CODE CONSISTING OF A NUMBER OF TRANSITIONS BETWEEN TWO INPUT CONDITIONS, A RING COUNTER HAVING A NUMBER OF STAGES, MEANS INCLUDING A SOURCE OF CLOCK PULSES FOR DRIVING SAID RING COUNTER THROUGH ONE COMPLETE CYCLE IN RESPONSE TO THE FIRST TRANSITION OF THE RECEIVED CODE, MEANS FOR COMPARING THE OUTPUT FROM SELECTED STAGES OF THE RING COUNTER WITH THE RECEIVED CODE ON THE RECEIVER LINE TO DETECT THE PRESENCE OF A TRANSITION IN AN UNDESIRED INTERVAL AND THE ABSENCE OF A TRANSITION IN A DESIRED INTERVAL, AN ALARM, SAID ALARM BEING ACTUATED UPON COMPLETION OF THE RING COUNTER CYCLE ONLY WHEN THERE HAS BEEN NO TRANSITION IN AN UNDESIRED INTERVAL AND NO ABSENCE OF A TRANSITION IN A DESIRED INTERVAL.