Abstract: Parametric array Doppler sonar apparatus includes an acoustic lens containing a flat disk-like central portion and an annular outer portion serving as a convergent lens. Multiple transducers are positioned between the lens and the focal plane so as to launch collimated acoustic beams in specified directions through the central portion of the lens and to receive reflected energy propagating principally through the annular portion of the lens.

Abstract: A fast time constant circuit includes input and output amplifier means coupled together through an R-C network containing a series capacitor and a shunt-connected constant current source in which the level of current flow through the current source is regulated by means of a remote adjustable d.c. voltage source.

Abstract: An apparatus for processing surface acoustic waves includes input and output transducers mounted on a piezoelectric substrate so as to launch and receive acoustic waves, respectively. Two pairs of reflective arrays are positioned in the propagation path between the input and output transducers so as to provide an S-shaped propagation path in which the directions of propagation of the waves launched by the input transducer and received by the output transducer are essentially parallel.

Abstract: Direct current error signals of either polarity are converted to a unipolar voltage and used to offset a triangular timing wave. The offset wave is applied to threshold amplifier so as to produce pulse width modulated signals. The pulse width modulated signals, together with a polarized direction signal and a clock signal from the triangular wave source, is applied to a servo amplifier containing first and second channels, each containing a flip flop for opening the associated channel in accordance with the polarity of the direction signal so as to pass direct or inverted pulse width modulating signals, respectively, through amplifier and filter circuits to the output terminal. Each of the amplifier circuits has a current sensing resistor, and a switching transistor arranged to switch the associated flip flop and thereby open that channel whenever the current through the sensing resistor exceeds a predetermined level.

Abstract: An autopilot automatically adjusts the sensitivity of a ship's steering system to accommodate changes in speed as well as sea and wind conditions. The autopilot utilizes heading error, speed and speed squared signals to produce a rudder order signal for controlling rudder position. The rudder order signal is developed in a heading keeping circuit unless a heading change greater than a predetermined threshold is commanded, in which event a programmer substitutes a heading change circuit for the heading keeping circuit. The sensitivity of the heading change circuit is automatically adjusted as an inverse function of vessel speed squared, and automatic rudder order limits are established in the same circuit as an inverse function of speed. The sensitivity of the heading keeping circuit is adjusted in accordance with a signal from an automatic gain control circuit which derives a performance index J from ship's speed, heading error and rudder order signals occurring during a given measurement interval.

Abstract: A d.c. load is energized through a full wave bridge circuit from an a.c. source in accordance with a d.c. control signal. The d.c. control signal is modulated so as to produce a train of unipolar pulses having pulse widths proportional to the magnitude of the d.c. control signal and synchronized so that the midpoints of successive pulses occur at the peaks of successive half cycles of the a.c. source voltage. A steering network couples the modulated width pulses to either a first or second transistor means in the bridge circuit depending upon the polarity of the d.c. control signal. The selected transistor means is saturated throughout the occurrence of an applied modulated width pulse and arranged so that energizing current is passed through the load in a forward or reverse direction, respectively, depending upon which of the transistor means is actuated.

Abstract: An acoustic lens for marine doppler sonar apparatus of the type in which acoustic energy is radiated and received along a beam directed at an angle with respect to a ship's axis is fabricated so as to have an external surface substantially flush with the ship's hull and an internal surface angularly disposed with respect to the external surface. Electro-acoustic transformation elements are mounted on the internal surface. The lens material is selected to have an acoustic propagation velocity greater than that of water so that acoustic signals are refracted in passing across the lens-water interface. The lens prevents spurious acoustic signals that would ordinarily be reflected from the aerated water close to the ship's hull from reaching the electro-acoustic transformation elements.

Abstract: Apparatus for detecting malfunctions in rudder-type steering systems utilizes electrical order and rudder angle signals. The rudder-order signal is applied to a closed-loop simulator that includes integrating apparatus adjusted to provide a time-variant simulated rudder angle signal which varies in the same manner that the actual rudder angle signal would vary in the absence of a malfunction when exposed to the same rudder error signal. The simulated and actual rudder angle signals are compared in a summing amplifier whose output is applied to a thresholding circuit which actuates an alarm whenever the instantaneous values of the simulated and actual rudder angle signals differ by more than a predetermined amount.

Abstract: A data recorder comprising a recording medium in the form of an endless loop of magnetic tape, and one or more magnetic heads, the magnetic tape being wound around former means comprising a plurality of rotatable members to provide a tape store, the rotatable members and inner turn of tape defining within the center of the store an area in which the or each magnetic head is mounted.

Abstract: Each output signal from a synchro device is applied to an individual voltage comparator through a step-down transformer. Each comparator is biased to a predetermined threshold level and produces an output signal whenever the magnitude of the associated synchro signal exceeds the threshold in the proper polarity. The comparator output voltages are applied to individual clocked flip-flops so as to produce binary output signals in a parallel format indicative of the rotor displacement of the synchro device.

Abstract: Two embodiments of a zero speed calibrator for a known type of electro-magnetic underwater log are disclosed. In a presently preferred embodiment, switching means are provided to connect the excitation source of the log to the magnetic field-generating coil in the sensor unit during normal operation, but to disconnect the excitation source from the coil and substitute dummy loads across the excitation source and the coil, respectively, during zero calibration procedures without disturbing the voltage-sensing circuit. In another embodiment, a special cable segment is inserted in the connecting cable during zero calibration procedures. The special cable segment contains dummy loads constructed so that insertion of the special segment automatically connects the dummy loads across the source and coil, respectively, while still providing a direct connection in the voltage-sensing circuit.

Abstract: A switching circuit which is actuated when the frequency of an input signal falls below a specified value, includes an input circuit for providing a rectangular pulse train consisting of pulses having durations indicative of the frequency of the input signal. The rectangular wave train is used to actuate a pair of one-shot multivibrators adjusted to produce output pulses having durations such that the pulses from the first one-shot correspond to an upper reference frequency slightly below that of a nominal input frequency, and the pulses from the second one-shot correspond to a lower reference frequency equal to the minimum acceptable input frequency. The output signals from the one-shot multivibrators are applied to clock terminals of first and second edge-triggered flip-flops, whereas the D input terminals of the same flip-flops are actuated by the rectangular pulse train.