Visual frequency indicator for broad band sonar monitor

Claim 1

AN APPARATUS FOR DETERMINING AND INDICATING THE FREQUENCY OF A RECEIVED INPUT SIGNAL COMPRISING IN COMBINATION A FIRST CHANNEL RESPONSIVE TO SAID INPUT SIGNAL HAVING TRANSLATIONAL HETERODYNING MEANS FOR FREQUENCY SHIFTING SAID INPUT SIGNAL TO A FIRST OUTPUT SIGNAL OF PREDETERMINED FREQUENCY, A SECOND CHANNEL RESPONSIVE TO SAID INPUT SIGNAL HAVING MEANS FOR DELAYING SAID INPUT SIGNAL A PREDETERMINED PERIOD OF TIME, CORRELATION MEANS CONNECTED TO SAID TRANSLATION HETERODYNING MEANS AND SAID SIGNAL DELAYING MEANS FOR FREQUENCY SHIFTING SAID DELAYED SIGNAL TO A SECOND OUTPUT SIGNAL OF PREDETERMINED FREQUENCY, SAID FIRST AND SECOND OUTPUT SIGNALS HAVING A DIFFERENCE IN PHASE PROPORTIONAL TO THE FREQUENCY OF SAID RECEIVED INPUT SIGNAL, AND MEANS CONNECTED TO SAID INPUT SIGNAL FREQUENCY SHIFTING MEANS AND SAID DELAYED SIGNAL FREQUENCY SHIFTING MEANS FOR MEASURING THE PHASE DIFFERENCE OF SAID FIRST AND SECOND OUTPUT SIGNALS AND INDICATING SAME AS THE FREQUENCY OF SAID RECEIVED INPUT SIGNAL.