Abstract: Disclosed is a low noise amplifier capable of handling large signals without significant distortion and which is particularly useful as the first electronic stage in hydrophone array systems utilizing piezoelectric sensor elements. The amplifier comprises three stages. The first stage uses an input field effect transistor (FET), which is protected against overload by very low leakage current diodes, and which acts as a voltage-to-current converter. The second stage comprises a junction transistor connected in a common emitter configuration which acts as a current-to-voltage converter. The third stage is a further junction transistor connected as an emitter follower. The overall gain of the amplifier is controlled by a feedback connection from the third stage to the first stage. The second and third stages are powered by a bipolar power supply.

Abstract: Apparatus for comparing an unknown signal with a reference signal is adapted to determine their ratio and, where a variation exists, to compensate the unknown signal to achieve unity ratio. The apparatus includes circuit means connectable to the signals for obtaining sum and difference signals. Means responsive to the sum and difference signals produce a control signal representing the product of these signals and feedback means responsive to the control signal generate a time-averaged feedback signal that is a measure of the ratio of the mean squares of the unknown and reference signals. Control means are disposed in the path of the unknown signal and are responsive to the feedback signal for varying the amplitude of the unknown signal to equilibrate and stabilize the apparatus when the mean squares of the reference signal and the compensated unknown signal are equal.

Abstract: An acoustic direction finder which identifies and displays bearing of an underwater received signal without the requirement of scanning the ambient space. The output signals of hydrophones at the ends of a pair of orthogonally located dipoles are applied to differential amplifiers to provide orthogonal dipole response characteristics, and an in-phase sum of the signal at the center of the dipoles is obtained. The differential amplifier output signals are integrated and the resultant signals are applied to individual multiplying means with the sum signal whereby a pair of X and Y coordinate deflection signals are obtained, which are applied to a display device.