The United States of America

Michael T McCord

Larry E Ivey

The frequency modulated monitor hydrophone system which is used to monitor low frequency sound signals where cross-talk coupling is a problem, consisting of a hydrophone, preamplifier and receiver which includes a control group. The hydrophone comprises an acoustic sensor and low-noise preamplifier utilizing dynamic range compression to condition the electrical acoustic sensor signal before it is frequency modulated (FM) and applied to a coaxial cable. At the remotely located receiver, the FM signal from the hydrophone preamplifier is filtered to remove undesirable signals, such as audio spectrum crosstalk and out of band signals. The partially recovered audio signal is decompressed utilizing dynamic range decompression, amplified, and output for utilization or recordation by an operator. A calibration circuit provides a continuity or partial calibration check for the hydrophone by applying a signal of predetermined frequency and voltage to the hydrophone preamplifier and sensor. A microprocessor in the control group periodically reads the input signal and controls the various receiver and hydrophone preamplifier circuits. Selected controls on the panel of the control group allows the operator to set gains, perform the calibration procedures, and monitor system performance.

Frequency-modulated monitor hydrophone system

A hydrophone preamplifier control unit provides for front panel controls and cable connectors for applying a calibration current and operating voltage to the hydrophone, controlling the level of these voltages, and monitoring the operation of the hydrophone. The control unit assures the continuity of the electrical circuits to a hydrophone through the use of a calibration current applied to the hydrophone through the use of a calibration current applied to the hydrophone through an interconnecting cable.

Hydrophone preamplifier control unit

A hydrophone preamplifier design utilizing hybrid integrated circuits, surface mounted components, multi-layered circuit boards and gain switching. Acoustic signals from a sensor are applied to a hybrid integrated circuit preamplifier whose gain is controlled by a relay activated remotely from a control that allows a predetermined attenuation permitting measurements of high sound pressure levels (low gain) or low ambient noise levels (high gain). The preamplifier in the hybrid integrated circuit provides a gain of 10 (20 dB) and an additional gain of 10 is provided by a low-noise operational amplifier (op amp). A current booster provides the output current drive capability for the preamplifier which is capable of driving large capacitive loads and has protection against both electrical and thermal overloads. Insertion calibration is provided through an ac current signal supplied by an external source, which develops a small voltage signal when supplied to the preamplifier. The voltage signal is coupled through an acoustic sensor to the preamplifier input providing a complete loop-back system test.

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Orlando, FL, United States of America

Michael T McCord