Underwater Acoustic Telemetry

Abstract

Equipment developed for test and use in a feasibility study of an acoustic FM/FM telemetering system is described. The system employs two standard subcarrier oscillators at 0.96- and 1.3-kc frequency modulating a 40-kc carrier to provide channels of continuous information. The objective has been to determine the effect on recovered data of such underwater acoustic phenomena as multipath transmission, Doppler, amplitude modulations and phase modulations. The various sea tests and their results are discussed. The quality of recovered data under favorable conditions are comparable to that of conventional radio frequency FM/FM telemetry. Interference when present appears to evolve about time variation of propagation loss which results as a very low frequency amplitude modulation of the carrier, AM of 5 to 100% has been noted. Operation in shallow water 50–150 ft presents greatest challenge. Range and data recovery agree with calculated performance. It was found that the transducer can be operated at resonance with a frequency deviation of ±15%. With variation in Q of 2 to 20, a comparison of recovered data indicates no appreciable deterioration.