In a method and apparatus for detecting a message in a signal the message begins with a preamble consisting of a fixed sequence of symbols, each having a symbol time T, modulated by repetitions of a higher rate code having low autocorrelation at lags anything other than zero. The repetitive code and the fixed sequence of symbols is known at the detector. The method comprises correlating the signal with the repetitive code; autocorrelating the signal with a copy of the signal, which is delayed su...

A static fluid system for detecting a selected change in an ambient condition. The system includes an elongate closed fluid line having a selected absolute pressure and pressure means to maintain the line pressure. Sensing means in the line respond to selected changes in ambient conditions to open the line and change the line to ambient pressure. Signal means responds to the change in line pressure, and flow restricting means in the line maintains the line pressure under normal ambient condition...

Apparatus for monitoring gas content on a site, to provide an indication if an undesirable gas content occurs, comprises a transmitter for feeding ultrasonic waves through the gas to a receiver. The ultrasonic waves are frequency-modulated and the phase of the modulation at the receiver relative to that at the transmitter is monitored. Either the relative phase is maintained constant, for example by a phase-locked loop so that the modulation frequency varies as a function of the gas content, or ...

A detection circuitry designed to sense a composite signal of the type such as composite frequency shift keying (FSK) 50% amplitude modulated (AM) signal or pulse code modulated return to zero FSK type signal. The circuitry includes means for separating the composite signal into its constituent components and means for converting the separated signals into an amplitude envelope signal and a differentiated DC component. The circuitry includes a trigger circuitry for providing an output signal whe...

In a computerized axial tomographic apparatus it is proposed to use, as radiation detectors, alkali halide scintillator crystals cooperating with photodiodes to measure the light output therefrom, or else photodiodes directly sensitive to the radiation passed through the patient. For advantageous operation, especially in regard to drift and rapidity of operation, it is proposed to use the photodiodes photovoltaically and in the so-called "current mode".

A battery-powered fire alarm including a smoke detector, a controllable horn circuit and a battery monitoring circuit. The smoke detector employs a pair of complementary field-effect transistor switches with gates respectively connected to an ionization chamber and a potentiometer of a Wheatstone bridge circuit connected across the battery. The field-effect transistors are biased off to minimize standby power consumption and are connected such that the threshold voltages thereof are offsetting t...

A flame detecting apparatus in which a detecting electrode is disposed in a flame, the base of a transistor is connected to the detecting electrode and biased with a predetermined DC voltage derived from a biasing circuit, the biasing circuit including a resistor and the impedance of the flame, an AC signal is applied to the emitter of the transistor, and an amplified AC signal is derived from the collector of the transistor as an output signal; the output signal being used as a control signal f...

This invention relates to detecting devices and more particularly to a new nd improved torpedo detection streamer having a plurality of microphonic detecting devices arranged therein in such a manner as to render the detection streamer substantially directionally and uniformly responsive to sound signals received from torpedoes passing above or below the streamer at any point along the length thereof.

A composition of matter for detecting glycolate incapacitating chemical agents; the composition of matter having the generic formula ##SPC1## Wherein R is an amino or imino group, the glycolate agents having the generic formula ##SPC2## Wherein R, R.sup.1, and R.sup.11 are each any aromatic group, any aliphatic group, any substituted aromatic group, any substituted aliphatic group, any cyclo aliphatic group, any cyclo aliphatic group having nitrogen in the cyclic structure, and any combinations ...

An alarm system comprising an elongate and flexible pressure line adapted to be charged with a selected line pressure; switching means coupled to the line and responsive to a pressure change in the line to create alarm signal; union means inserted in frictional sealing engagement within said line and having a bore which maintains the fluid continuity of the line; and spring-biased retaining means circumscribing said line and applying a selected clamping force to seal said union means in said lin...