Personal call system

Claim 1

A PERSONAL CALL SYSTEM FOR SELECTIVELY CALLING A PLURALITY OF INDIVIDUALS IN A GIVEN AREA, COMPRISING A CLOSED LOOP CIRCUIT IN SAID AREA, A CARRIER FREQUENCY GENERATOR, A MODULATING FREQUENCY GENERATOR TUNABLE TO A PLURALITY OF MODULATING FREQUENCIES LOWER THAN THE FREQUENCY OF SAID CARRIER GENERATOR, MEANS COMPRISING A SET OF SELECTOR MEMBERS CONNECTED TO SAID MODULATING FREQUENCY GENERATOR EACH OPERABLE INDIVIDUALLY FOR TUNING SAID MODULATING FREQUENCY GENERATOR TO A CORRESPONDING ONE OF SAID MODULATING FREQUENCIES, A MODULATOR COUPLED WITH SAID CARRIER GENERATOR AND SAID MODULATING FREQUENCY GENERATOR TO MODULATE THE CARRIER WITH THE SELECTED MODULATING FREQUENCY, A TRANSMITTER CONNECTED TO SUPPLY THE OUTPUT ENERGY OF SAID MODULATOR TO SAID LOOP CIRCUIT, MEANS OPERABLE BY ANY ONE OF SAID SELECTOR MEMBERS FOR INTIATING THE TRANSMISSION OF SAID MODULATED CARRIER TO SAID LOOP CIRCUIT, A TIMING CIRCUIT HAVING MEANS ACTUATED BY OPERATION OF ANY ONE OF SAID SELECTOR MEMBERS TO INTERRUPT THE TRANSMISSION OF SAID MODULATED CARRIER TO SAID LOOP CIRCUIT AFTER A SUITABLE TIME INTERVAL, AND A PLURALITY OF PORTABLE RECEIVERS EACH CONSTRUCTED TO BE CARRIED BY A RESPECTIVE ONE OF THE INDIVIDUALS TO BE PAGED, EACH RECEIVER COMPRISING MEANS FOR RECEIVING AND DETECTING THE SIGNAL SUPPLIED TO SAID LOOP CIRCUIT, RESONANCE RELAY MECHANICALLY TUNED TO ONE OF SAID MODULATING FREQUENCIES WHICH IS CHARACTERISTIC FOR THE INDIVIDUAL CARRYING THE RECEIVER, MEANS TO APPLY THE DETECTED SIGNAL TO SAID RESONANCE RELAY, AND MEANS CONTROLLED BY SAID RESONANCE RELAY TO PRODUCE AN AUDIBLE SIGNAL WHEN SAID RELAY IS ACTUATED, AN ELECTROMAGNETIC SELECTOR SWITCH HAVING A DRIVING MAGNET, A PLURALITY OF SWITCH ARMS AND A PLURALITY OF SEPARATE BANKS OF CONTACTS, EACH BANK OF CONTACTS COOPERATING WITH A CORRESPONDING ONE OF SAID SWITCH ARMS, A PLURALITY OF FREQUENCY DETERMINING IMPENDANCES IN SAID MODULATING FREQUENCY GENERATOR CONNECTED WITH THE CONTACTS OF AT LEAST ONE OF SAID BANKS AND CONNECTED SO AS TO BE PUT IN CIRCUIT BY THE RESPECTIVE SWITCH ARM, MEANS ACTUATED BY OPERATION OF ANY ONE OF SAID SELECTOR MEMBERS FOR STARTING SAID SELECTOR SWITCH, AND MEANS FOR STOPPING SAID SELECTOR SWITCH WHEN A POSITION DETERMINED BY THE ACTUATED SELECTOR MEMBER IS REACHED WHEREBY THE MODULATING FREQUENCY IS ADJUSTED TO THE DESIRED VALUE.