Sine-cosine frequency tracker

Claim 1

A FREQUENCY TRACKER COMPRISING, AN ADJUSTABLE GENERATOR EMITTING AT LEAST ONE ALTERNATING CURRENT SIGNAL, A SOURCE OF SIGNALS OF UNKNOWN FREQUENCY, FIRST MODULATOR MEANS FOR OBTAINING A FIRST BEAT FREQUENCY SIGNAL FROM SAID ADJUSTABLE GENERATOR OUTPUT SIGNAL AND SAID SIGNALS OF UNKNOWN FREQUENCY, SECOND MODULATOR MEANS FOR OBTAINING A SECOND BEAT FREQUENCY SIGNAL FROM SAID ADJUSTABLE GENERATOR OUTPUT SIGNAL AND SAID SIGNALS OF UNKNOWN FREQUENCY, MEANS CAUSING THE PHASE OF SAID SECOND BEAT FREQUENCY SIGNAL EITHER TO LAG OR TO LEAD THE PHASE OF SAID FIRST BEAT FREQUENCY SIGNAL BY 90* DEPENDING ON THE SENSE OF THE DIFFERENCE IN FREQUENCY OF SAID GENERATOR SIGNAL AND SAID SIGNAL OF UNKNOWN FREQUENCY, A PAIR OF SIMILAR FILTERS RESPECTIVELY FILTERING SAID FIRST AND SECOND BEAT FREQUENCY SIGNALS, A PHASE LAG CIRCUIT ENERGIZED BY THE OUTPUT OF ONE OF SAID FILTERS, A PHASE LEAD CIRCUIT ENERGIZED BY THE OUTPUT OF THE OTHER OF SAID FILTERS, THE SIGNAL OUTPUTS OF SAID PHASE LAG AND LEAD CIRCUITS HAVING A RELATIVE PHASE SEPARATION WHICH DIFFERS BY 90* FROM THE PHASE SEPARATION OF THE SIGNALS APPLIED TO THE INPUT THEREOF, SAID 90* PHASE DIFFERENCE BEING UNAFFECTED BY CHANGES IN FREQUENCY, A BALANCED MULTIPLIER MULTIPLYING SAID EMITTED TWO SIGNALS TO FORM A DIRECT-CURRENT ERROR SIGNAL, MEANS INTEGRATING SAID ERROR SIGNAL TO FORM AN INTEGRAL SIGNAL, AND MEANS APPLYING SAID INTEGRAL SIGNAL TO CONTROL THE FREQUENCY OF SAID GENERATOR SO AS TO REDUCE SAID ERROR SIGNAL AMPLITUDE.