Echo ranging apparatus

Claim 1

APPARATUS FOR DETECTING AN OBSTACLE IN THE VICINITY OF A BOAT, COMPRISING A MEANS FOR GENERATING AND RADIATING IN AIR COMPRESSIONAL WAVES OF ULTRASONIC FREQUENCY MODULATED SEQUENTIALLY BY WAVES OF TWO DIFFERENT AUDIO FREQUENCIES, A PAIR OF MICROPHONES CARRIED BY THE BOAT AND DISPOSED ON OPPOSITE SIDES OF THE FORWARD PATH OF TRAVEL OF SAID BOAT TO PICK UP THE MODULATED COMPRESIONAL WAVES AFTER REFLECTION IN AIR FROM SAID OBSTACLE, A RECEIVER HAVING TWO CHANNELS, EACH OF SAID CHANNELS INCLUDING AN ULTRASONIC FREQUENCY TUNED ELECTRICAL AMPLIFIER, A DEMODULATOR, AUDIO AMPLIFIER AND BALANCED MODULATOR ALL CONNECTED TOGETHER IN SEQUENCE, MEANS FOR APPLYING SIGNALS OF SAID TWO DIFFERENT AUDIO FREQUENCIES TO THE BALANCED MODULATORS RESPECTIVELY OF THE TWO CHANNELS SAID MICROPHONES BEING CONNECTED TO THE TUNED AMPLIFIERS RESPECTIVELY, AND A PHASE METER HAVING OPPOSING INPUT TERMINALS AND CALIBRATED WITH AZIMUTH INDICATIONS CORRESPONDING TO PHASE DIFFERENCES OF SIGNALS APPLIED TO OPPOSING INPUT TERMINALS OF THE PHASE METER, SAID PHASE METER BEING CONNECTED TO THE BALANCED MODULATORS OF BOTH CHANNELS FOR INDICATING ANY DIFFERENCE IN PHASE BETWEEN THE SIGNALS APPLIED BY THE MODULATORS TO RESPECTIVE TERMINALS OF THE PHASE METER, WHEREBY SAID METER INDICATES THE AZIMUTH OF LOCATION OF SAID OBSTACLE WITH RESPECT TO THE FORWARD PATH OF TRAVEL OF THE BOAT.