SHORT RANGE COMMUNICATIONS

THIS PROPOSAL PROVIDES A NOVEL AND INNOVATIVE SOLUTION TO THE PROBLEM OF SHORT RANGE (UP TO 1000 YARDS) UNDERWATER COMMUNICATION UNDER VARIABLE SOUND PROPAGATION CONDITIONS. THE PROPOSED CONCEPT IS TO ADAPT THE FREQUENCY MODULATION FEEDBACK (FMFB) PRINCIPLE WHICH HAS BEEN WELL PROVEN IN MICROWAVE RADIO TRANSMISSION TO THE UNDERWATER ACOUSTIC ENVIRONMENT. AT THE TRANSMITTER, A WIDEBAND HIGH DEVIATION RATIO ACOUSTIC SIGNAL -AT A HIGH CARRIER FREQUENCY -WILL BE PROJECTED INTO THE WATER AND RECEIVED BY A SUPERHETERODYNE ACOUSTIC RECEIVER WITH A WIDEBAND "FRONT END". HOWEVER, A LOCAL OSCILLATOR CONSISTING OF A VOLTAGE CONTROLLED OSCIALLATOR (VCO) WHOSE VOLTAGE INPUT IS A FEEDBACK SIGNAL FROM THE FM-DETECTED WAVEFORM WILL PRODUCE A NARROWBAND INTERMEDIATE FREQUENCY (IF). THE WIDEBAND FRONT-END WILL HELP TO OVERCOME ACOUSTIC PROPAGATION ANOMALIES, WHEREAS THE NARROWBAND IF WILL RESULT IN GOOD THRESHOLD CHARACTERISTICS.