Frequency-modulated monitor hydrophone system

Abstract

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.

What is claimed is: 
     
       1. A monitor hydrophone system comprised of: a hydrophone for detecting changes of acoustic pressure in a medium and converting the changes in acoustic pressure into electrical signals;   a means for preamplifying the electrical signals from the hydrophone;   a receiver for receiving the electrical signals and processing them to provide a processed signal;   a means for controlling hydrophone electrical signal and the receiver, and monitoring a plurality of inputs and outputs;   a means for generating a predetermined direct current voltage and current to operate the hydrophone, receiver, and control means;   a means for recording and displaying the processed signal for operation and analysis at a later period; and   a means for calibrating the hydrophone to assure continuity.   
     
     
       2. A monitor hydrophone system, as in claim 1, wherein the hydrophone further comprises a sensor and preamplifier wherein the electrical signal is compressed utilizing dynamic range compression and converted into a frequency modulated signal. 
     
     
       3. A monitor hydrophone system, as in claim 2, wherein the receiver is further comprised of means for decompressing the frequency modulated signal, and filtering out noise and out-of-band signals to produce the processed signal. 
     
     
       4. A monitor hydrophone system, as in claim 1, wherein the means for conducting is a coaxial cable having a plurality of conductors for conducting the electrical signal to the receiver, conducting the means for calibrating from the control means to the hydrophone and back to the control means, and conducting system power from the means for generating electrical power to the hydrophone. 
     
     
       5. A monitor hydrophone system, as in claim 1, wherein the hydrophone is further comprised of a means for converting the preamplified electrical signal to an optical signal prior to being applied to the receiver, a means for conducting the optical signal from the preamplifier means to the receiver, and a means in the receiver for converting the optical signal to a second preamplified electrical signal to be processed in the receiver. 
     
     
       6. A monitor hydrophone system, as in claim 5, wherein the means for conducting is a cable having a plurality of fiber optical for conducting an optical signal from the hydrophone to the receiver and for conducting the means for calibrating from the control means to the hydrophone and back to the control means, and a plurality of metallic conductors for conducting system power from the means for generating electrical power to the hydrophone.