There is disclosed frequency modulation (FM) or phase modulation (PM) communication with a receiver having a limiter, in spread-spectrum operation for security purposes. The spectrum is spread on transmission by superimposing a psuedo-noise code modulation on the intelligence modulation of the carrier. On reception the spectrum is collapsed by auto-correlation of the pseudo-noise code. The pseudo-noise spectrum is produced by a digital coder which causes phase modulation of the carrier at the tr...

There is disclosed apparatus and a method for producing a selected visual pattern. A colliminated linearly-polarized laser beam of radiation, is passed in succession through, and subdivided into a matrix of potentially visual elements by, a pair of matrices of coextensive light-modulating cells, each cell matrix formed by crossed arrays of electro-optic crystals disposed with their optic axes at right angles to the beam and at right angles to each other. Voltage is impressed on selected crystals...

Amplitude modulation systems for underwater communication have a number of disadvantages. For example, with a number of divers attempting to communicate simultaneously, intolerable cross-talk occurs. Variable tuning is necessary to overcome this problem. However, the invention disclosed herein uses angle modulation (phase or frequency modulation) which inherently has fewer noise problems and, because of the "capture effect" reduces any cross-talk problems. In an exemplary embodiment an audio tra...

A digital communication system for the transmission of digital data with a modulated carrier uses a modulation locked loop and pseudo-random code to develop synchronization signals for the digital data signals and to ensure a high level of communication reliability.

The invention is concerned with the interconnection of communications units such as telephones, microphones and loudspeakers. According to the invention a connecting plate extends between the undersurfaces of adjacent units and locates the units in the desired spatial relationship. Jointing means then detachably connect the unit to the plate.

A television receiver is provided comprising a variable frequency local oscillator and frequency synthesizer control means for controlling the frequency of the variable frequency local oscillator in accordance with the setting of variable divider means for effecting channel or frequency tuning of said receiver, the frequency synthesis control means comprising first divider means operable on the output of the variable frequency local oscillator, the first divider means being set to one of a plura...

A communication system for communicating between a central control unit and a plurality of controlled units, all interconnected by a single communication channel, wherein communication is time multiplexed with control words being transmitted in each direction during each time interval allocated to each separate controlled unit. The control words are transmitted during half-cycles of a periodic clock signal of one polarity, while data from the controlled units may be transmitted to the central co...

A half-duplex digitally-controlled telephone communication apparatus for permitting half-duplex communication between local and remote subscribers. Analog speech of one subscriber to be transmitted to the other subscriber is converted to a digital format, processed by real-time speech processing apparatus, stored in a delay buffer, and processed in modem apparatus for transmission to the other subscriber. In accordance with the present invention, the delay buffer provides a delay of a sufficient...

In a pulse code modulation system, a source of key signals comprising a source of random pulses, multisection delay device, means for applying said pulses to said multisection delay device, apparatus for combining the outputs of predetermined sections of said delay device and apparatus for enciphering pulse code modulation signals by combining said signals with said combined output from said sections of said multisection delay device.

A communication cable is composed of a number of optical fibers with an outer coating, loosely twisted together to form basic groups, provided with tension-relieving wires and sheathed to form a cable while filling the interspaces with lubricants.