Frequency discriminating circuit

Claim 1

A CIRCUIT FOR DISCRIMINATING AS TO FREQUENCY OF AN APPLIED SIGNAL THAT PERIODICALLY ALTERNATES ABOUT A PARTICULAR REFERENCE AMPLITUDE LEVEL WHICH HAS CHARACTERISTIC FREQUENCIES THAT MAY FALL WITHIN A PREDETERMINED REFERENCE BAND OF FREQUENCIES OR OUTSIDE SAID PREDETERMINED REFERENCE BAND OF FREQUENCIES, COMPRISING: A ZERO CROSSING CIRCUIT FOR DETECTING EACH ZERO CROSSING TRAVERSE OF SAID APPLIED SIGNAL THROUGH SAID REFERENCE AMPLITUDE LEVEL AS SAID SIGNAL ATLERNATES ABOUT SAID REFERENCE AMPLITUDE LEVLE, SAID CIRCUIT SUPPLYING A RELATIVELY SHORT OUTPUT PULSES THEREBY OCCURING TRAVERSE AND SAID OUTPUT PULSES THEREBY OCCURING IN SUCCESSION AT A FREQUENCY WHICH DIRECTLY REPRESENTS THE FREQUENCY OF SAID APPLIED SIGNAL; A FIRST MULTIVIBRATOR CIRCUIT RESPOSIVE TO SUPPLY PUT PULSE FROM SAID ZERO CROSSING CIRCUIT TO SUPPLY A PULSE WHICH HAS A DURATION THAT IS SLIGHTLY LESS THAN THE DURATION OF A HALF-PERIOD OF THE HIGHEST FREQUENCY OF SAID APPLIED SIGNAL; A SECOND MULTIVIBRATOR CIRCUIT RESPONSIVE TO EACH PULSE FROM SAID FIRST MULTIVBRATOR CIRCUIT AS IT TERMINATES TO SUPPLY A REFERENCE PULSE RELATED IN SUCH A MANNER TO THE PULSE FROM SAID FIRST MULTIVIBRATOR CIRCUIT THAT THE COMBINED DURATION OF A PULSE FROM SAID FIRST MULTIVIBRATOR CIRCUIT AND THE RELATED REFERENCE PULSE FROM SAID SECOND MULTIVIBFATOR CIRCUIT IS AT LEAST AS GREAT AS THE DURATION OF A HALF-PERIOD OF THE LOWEST FREQUENCY OF SAID APPLIED SIGNAL; AND CIRCUIT MEANS RESPONSIVE TO A FREQUENCY REPRESENTING PULSE FROM SAID ZERO CROSSIN GGCIRCUIT AND A REFERENCE PULSE FROM SAID SECOND MULTIVIBRATOR CIRCUIT WHEN THEY OCCUR CONCURRENTLY TO SUPLY AN OUTPUT WHICH INDICATES THAT SAID APPLIED SIGNAL FALLS WITHIN SAID PREDETERMINED REFERENCE BAND OF FREQUENCIES.