Abstract: The operational amplifiers conventionally used in electronic analog compus can be replaced with fixed-gain differential amplifiers having no external negative feedback to control their gain. This allows a large increase in the bandwidth of the computers, with a resulting faster response time. Circuits for summing, integration, and differentiations are specifically disclosed using fixed-gain amplifiers.

Abstract: A high frequency active filter is presented having an amplifier having an en loop gain between one and three which is provided with appropriate electrical components of appropriate values for generating the desired filter configuration of pole-zero pairs with no intentional connection between the negative input terminal of the amplifier and the output terminal of the amplifier.

Abstract: An oscillator generates a fixed frequency ultrasonic output signal. After wer amplification this signal drives a transmitting transducer which projects an ultrasonic beam into water. Reflected signals are received by a receiving transducer and AGC preamplified. A chopper multiplies the received signal with the transmitted signal and generates an output signal if a target exists. To determine whether the target is a swimmer, this output signal is band pass filtered and amplified and then fed both to an automatic alarm and to a set of headphones. A human operator listening to the headphone output classifies the target and determines exact bearing.

Abstract: An a.c. coupled, low-pass translating filter in which quadrature phases of n input signal spectrum are, in three successive balanced modulator stages driven by quadrature phases of externally generated carrier signals, alternately modulated-up and demodulated-down, and the sum of the remaining spectra is, in a final stage, demodulated below the cutoff frequency. Each stage terminates with a low-pass filter in which odd harmonics of the carrier frequencies and double frequencies generated in the second and final stages are eliminated.

Abstract: An underwater intrusion alarm system using an array of one or more remotely eployable, acoustic doppler detector probes. Each probe is a unitary submersible buoy formed by a pair of vertically coaxially and acoustically isolated, right cylindrical active transducer elements that are shielded from surface and bottom reflections. Transmitter and receiver circuits may be located either in the buoy with an external connection to conveniently located headphones and alarms or at a distant site with a fixed wire connection to the buoy transducer elements. A depth sensitive ancilliary mechanism regulates the submergence of the buoy in conformance with the rise and fall of the tide.

Abstract: An electrical circuit for measuring the phase difference between a pair of nput signals by uniformly limiting selected properties of the waveforms describing the input signals and modulating an output signal in dependence upon the duration of contrariety between the unlimited properties of the input signals whereby error in the output signal due to "jitter" (i.e., abrupt, spurious variations in pulse amplitude or duration caused by superimposition of noise) is substantially eliminated. Various output means produce either a continuous wave analog signal or a digital bit signal in dependence upon the modulation of the output signal. Coupled ancillary circuitry monitors one input signal in comparison with the other input signal and provides an output signal signifying which input signal has a leading phase angle.