Induction field transmitter

Claim 1

A TRANSMITTER FOR GENERATING AN INDUCTION FIELD INCLUDING IN COMBINATION; ANTENNA MEANS INCLUDING A COIL WOUND ON A CORE OF FERROMAGNETIC MATERIAL, CAPACITOR MEANS COUPLED TO SAID COIL AND FORMING A RESONANT CIRCUIT THEREWITH, TRANSISTOR MEANS COUPLED TO SAID RESONANT CIRCUIT TO FORM AN OSCILLATOR, SAID OSCILLATOR PRODUCING AN ALTERNATING CURRENT SIGNAL HAVING A FREQUENCY DEPENDENT UPON THE INDUCTANCE OF SAID COIL, DIRECT CURRENT VOLTAGE SUPPLY MEANS CAPABLE OF HAVING DIFFERENT VOLTAGES COUPLED TO SAID COIL AND SAID TRANSISTOR MEANS TO FURNISH ENERGY TO SAID OSCILLATOR, SAID DIFFERENT VOLTAGES APPLIED TO SAID COIL CAUSING THE INDUCTANCE OF SAID COIL TO CHANGE, SAID COIL HAVING A PLURALITY OF TAPS THEREON FOR SELECTIVE CONNECTION TO SAID SUPPLY MEANS, SAID TAPS BEING LOCATED ON SAID COIL SO THAT THE INDUCTANCE OF THE CONNECTED PORTION OF SAID COIL HAS SUBSTANTIALLY THE SAME EFFECTIVE VALUE WITH DIFFERENT SUPPLY VOLTAGES APPLIED THERETO, WHEREBY THE FREQUENCY OF SAID OSCILLATOR MEANS IS MAINTAINED AT A PREDETERMINED FREQUENCY.