Test circuitry for measuring envelope distortion over a particular frequency range

Claim 1

A TEST SET FOR THE MEASUREMENT OF ENVELOPE DELAY COMPRISING, MEANS FOR GENERATING A PAIR OF TEST SIGNALS EACH OF WHICH CHANGES FREQUENCY-WISE IN THE SAME SENSE OVER A TIME INTERVAL SO THAT A SUBSTANTIALLY CONSTANT DIFFERENCE IN FREQUENCY IS MAINTAINED BETWEEN SAID TEST SIGNALS OVER SAID INTERVAL, A PHASE METER HAVING FIRST AND SECOND INPUT CIRCUITS, FIRST MEANS HAVING AN OUTPUT CIRCUIT COUPLED TO SAID MEANS FOR GENERATING FOR DERIVING A REFERENCE SIGNAL HAVING A FREQUENCY EQUAL TO THE DIFFERENCE BETWEEN THE FREQUENCIES OF SAID TEST SIGNALS, MEANS FOR COUPLING THE OUTPUT CIRCUIT OF SAID FIRST MEANS TO THE FIRST INPUT CIRCUIT OF SAID PHASE METER, A TEST CIRCUIT HAVING AN INPUT AND AN OUTPUT CIRCUIT, MEANS FOR APPLYING SAID TEST SIGNALS PRODUCED BY SAID MEANS FOR GENERATING TO THE INPUT CIRCUIT OF SAID TEST CIRCUIT, SECOND MEANS HAVING AN INPUT CIRCUIT AND AN OUTPUT CIRCUIT FOR DERIVING A SIGNAL HAVING A FREQUENCY EQUAL TO THE DIFFERENCE BETWEEN THE FREQUENCIES OF SAID TEST SIGNALS, MEANS FOR COUPLING THE INPUT CIRCUIT OF SAID SECOND MEANS TO THE OUTPUT CIRCUIT OF SAID TEST CIRCUIT; MEANS FOR COUPLING THE OUTPUT CIRCUIT OF SAID SECOND MEANS TO THE SECOND INPUT CIRCUIT OF SAID PHASE METER SO THAT SAID PHASE METER INDICATES THE ENVELOPE DELAY OF SAID TEST CIRCUIT OVER A PARTICULAR RANGE OF FREQUENCIES, SAID MEANS FOR GENERATING FURTHER COMPRISING FIRST MEANS FOR PRODUCING A FLUCTUATING SIGNAL, SECOND MEANS FOR PRODUCING A FLUCTUATING SIGNAL WHICH VARIES IN FREQUENCY OVER A GIVEN TIME INTERVAL, THIRD MEANS COUPLED TO THE OUTPUT CIRCUITS OF SAID FIRST AND SECOND MEANS FOR PRODUCING A SIGNAL HAVING A FREQUENCY EQUAL TO THE DIFFERENCE IN FREQUENCY BETWEEN THE FLUCTUATING SIGNALS PRODUCED BY SAID FIRST AND SECOND MEANS, FOURTH MEANS FOR PRODUCING A FLUCTUATING SIGNAL HAVING A FREQUENCY WHICH DIFFERS FROM THE FREQUENCY OF THE FLUCTUATING SIGNAL PRODUCED BY SAID FIRST MEANS, FIFTH MEANS COUPLED TO THE OUTPUT CIRCUITS OF SAID SECOND AND FOURTH MEANS FOR PRODUCING A FLUCTUATING SIGNAL HAVING A FREQUENCY SUBSTANTIALLY EQUAL TO THE DIFFERENCE IN FREQUENCY BETWEEN THE FLUCTUATING SIGNALS PRODUCED BY SAID SECOND AND FOURTH MEANS, SIXTH MEANS COUPLED TO THE OUTPUT CIRCUITS OF SAID THIRD AND FIFTH MEANS FOR DERIVING A SIGNAL HAVING A FREQUENCY SUBSTANTIALLY EQUAL TO THE DIFFERENCE IN FREQUENCY BETWEEN THE FLUCTUATING SIGNALS PRODUCED BY SAID FIRST AND FOURTH MEANS, A CLOCK PULSE GENERATOR, SEVENTH MEANS FOR COMPARING THE FREQUENCY OF THE SIGNAL PRODUCED BY SAID SIXTH MEANS WITH THE FREQUENCY OF A FLUCTUATING SIGNAL PRODUCED BY SAID CLOCK PULSE GENERATOR, MEANS RESPONSIVE TO A DIFFERENCE IN FREQUENCY OR PHASE BETWEEN THE SIGNAL PRODUCED BY SAID SIXTH MEANS AND THE SIGNAL PRODUCED BY SAID CLOCK PULSE GENERATOR FOR CHANGING THE FREQUENCY OF THE SIGNAL PRODUCED BY SAID FOURTH MEANS UNTIL THE DIFFERENCE IS ELIMINATED.