Abstract: An electro-acoustic terminal unit for use in an audio teleconferencing system comprises a loudspeaker and one or more microphones each having a sensitivity which is directionally dependent and exhibits at least one null or substantially null position. The loudspeaker and microphones are rigidly mounted on a boom and the microphones are so located and orientated relative to the loudspeaker that the null position is directed towards the loudspeaker.

Abstract: To transmit a number of individual speech channels over a smaller number of transmission channels, the frequency range of each speech channel is broken into sub-channels and each of these is considered separately for operational activity. Composite speech signals are then formed from the active frequency sub-channels of the individual speech channels and these are transmitted with coding signals indicative of their composition.

Abstract: A device for securing and anchoring a telephone wire comprises a narrow helix with widely spaced coils with an open bight at one end. The invention further comprises a telephone pole with an internal fixing element such as a ring with the device securing a wire looped onto it.

Abstract: Apparatus for winding tape around an elongate core comprises a frame structure which supports one or more reels of tape. The frame structure carries a bobbin which is rotatable with the frame structure about the core. Tape passes from the reel to the bobbin and extends between a pair of contacts before passing through a slit to the core. The contacts are normally open but if the tape touches one of these that contact closes and the speed of the motor, which drives the frame structure is adjusted to maintain the tape between the contacts. This arrangement ensures a substantially constant pitch of the tape around the core.

Abstract: The magnetic bias field required to collapse magnetic domains in an epitaxial liquid phase grown garnet is reduced by a method of depositing a layer of a suitable element, e.g. gallium or chromium, on the surface of the garnet after growth and then heating the garnet. The suitability of the element depends on its atomic diameter and affinity for oxygen.Propagation paths for bubbles in a magnetic bubble memory are defined by treating a garnet except where the propagation paths are required, by the method.

Abstract: An equalizer network that exhibits stability and may be cascaded with a transmission channel is disclosed. The network includes only two operational amplifiers, resistors and capacitors and provides a bump shaped amplitude characteristic at resonance frequency. The equalizer may be modified to exhibit selectively a `bump` or `dip` at resonance, and may be so constructed that trimming operations and the independent selection of parameters is facilitated.

Abstract: A lightning protector carrier comprises a lamellar element made of electrically insulating material and having a plurality of sets of holes therethrough each set of holes defining a respective socket to receive a respective lightning protector device, and a plurality of electrically conducting terminals for making electrical connection to lightning protector devices at a front face of the element. One hole of each set of holes accomodates a terminal and the terminals are electrically interconnected by one or more busbars at the rear of the element. At least the front surface of the element is shaped such that one hole of each set is separated from another hole of the set by a protruding portion of the element interposed between said one hole and said another hole.

Abstract: A digital-to-analogue converter which uses a technique of two-level quantization in order to generate a pulse density code signal which yields the analogue signal when filtered. Standard digital logic adders and registers are used in the conversion of PCM signals to the pulse density code. The adders and registers are arranged as a feedback loop in which an approximation signal capable of either a "high" or a "low" level is compared repetitively with a PCM signal and the difference is accumulated, but at the end of each operation the accumulated total is tested and the value of the approximation signal for the next cycle is chosen so as to reduce the accumulated total. The cycle period is set by a clock, and the approximation signal is the pulse density code signal. The noise spectrum of the pulse density code signal may be adjusted by the addition of an offset signal to the incoming PCM signal.

Abstract: A submarine telecommunications cable assembly includes a section of main submarine telecommunications cable electrically connected to a short length of cable extending from a repeater housing, the section of main cable being armoured at least in the proximity of the repeater. The electrical connection of the section of cable to the short length of cable extending from the repeater housing is positioned at a location spaced from the repeater housing and strengthening means are provided along the short length of cable substantially increasing the flexural rigidity of the short length of cable. The armouring of the main section of cable extends over the short length of cable and the strengthening means and is anchored to the repeater housing.

Abstract: Optical fibres and optical cables of improved bandwidth, especially intended for use in a communications system. Over-compensated and under-compensated fibres or cable sections are connected alternately so that each fibre or cable section tends to correct the modal dispersion originating in the previous fibre or cable section, giving a narrower overall impulse response and hence a better bandwidth. This arrangement also substantially reduces the variation of bandwidth with source wavelength.

Abstract: This invention relates to the rigging of wires, particularly telephone wires, between two elevated locations specifically two telegraph poles or a telegraph pole and a location on the upper part of a building. The telephone wire to be rigged is fed around the pulley of a pulley block. The block is attached to the end of the sash line which emerges from the pole top and the block carrying the loop of wire hoisted to an elevated position. The free end of the wire is then fixed to the other elevated location for example the side of a house and the wire drawn tight to its working position. By manipulation of the other end of the sash line and the wire the pulley block carrying the loop of the wire is guided into the top of the pole, down through the interior of the pole and out through the access aperture in the lower part of the pole. The wire is then secured in the pole, the loop is severed and the appropriate electrical terminations made.

Abstract: A balanced/unbalanced converter circuit for connection to a subscriber's telephone line. A first Darlington transistor pair is connected as a controllable impedance between a first supply terminal and a first balanced input/output terminal. A second Darlington transistor pair is likewise connected between a second supply terminal and a second balanced terminal. A potential-summing resistive network is connected between the balanced terminals and the sum-representative potential is compared with a reference to provide a control signal to simultaneously change the impedances in opposite directions to correct any departure from balance. A third transistor controllable impedance circuit is connected in series with one Darlington transistor pair and used to regulate direct current flow through the line.

Abstract: A power supply circuit for providing a local power supply replenished from the exchange for a telephone instrument. An electrical energy storage device is connected in parallel with an impedance by a device providing a unidirectional transfer of electrical energy from a direct current path through the impedance. A by-pass circuit is connected in parallel with the impedance. The impedance is a zener diode, the storage device is a capacitor, the unidirectional transfer device is a diode, and the by-pass circuit is a transistor responsive to the state of charge of the capacitor. A trickle charge circuit is connected to transfer energy to the capacitor irrespective of the by-pass circuit and a speech-frequency by-pass circuit is in parallel with the zener diode. A switch responsive to on-hook/off-hook conditions is used to confine energy storage to off-hook periods.

Abstract: The surface of a semiconductor is prepared by electrolytically removing the surface of the semiconductor. A two component electrolyte is used. A first component forms an oxide on the surface of the semiconductor and the second component dissolves the oxide.

Abstract: An information handling apparatus capable of having a large number of input/output ports includes a plurality of independent processors connected to respective positions around a plurality of closed rings of shifting registers arranged in parallel which form the main storage medium for the apparatus.

Abstract: A rear feed assembly for a microwave aerial, comprising a dielectric support member having an energy reflecting surface positioned against one face thereof. Waveguide means is connected with the support, the center of the waveguide aperture being the phase center of the assembly and the said face of the support being located in the far field region with respect to that center. The support is so shaped that energy emitted from the waveguide means is reflected from the reflecting surface and emerges through a second face of the support with a spherical wavefront centered on the image phase center.

Abstract: An opto-electronic element consists of a dielectric optical waveguide having a single crystal core of meta-nitroaniline. The element is made by feeding molten meta-nitroaniline into a hollow fibre along which a temperature gradient exists. Nucleation sets in at one end of the fibre and the temperature gradient is altered to promote crystal growth along the fibre. The element can be used as a polarizer, in isolators, harmonic generators or mixers. The action of the device depends on either the non-linear optical properties of the meta-nitroaniline or the optical anisotropy of the meta-nitroaniline. To make a polarizer the meta-nitroaniline core is surrounded by a cladding having a refractive index lying midway between two of the refractive indices of the meta-nitroaniline.

Abstract: A communications cable comprises a single optical fibre enclosed in a sheathing assembly which protects the fibre against shock and bending. The sheathing assembly comprises end members and a protective sheath surrounded preferably by a coiled spring.

Abstract: The electrochemical measuring technique of the present invention employs, as the barrier material, a concentrated electrolyte, which also forms a medium for the controlled dissolution of a surface of the semiconductor so as to provide a continuous depth profile. The depth profile characteristic may be determined by capacitance-voltage measurements on n-type bulk GaAs, using KOH as the electrolyte.

Abstract: Apparatus for stabilizing the output characteristics of an injection laser has a device for producing an electrical pulse train representative of an optical pulse train of the laser. The electrical pulse train is fed to circuitry which monitors the switch-on delay of the laser and controls the bias current of the laser such that the switch-on delay is maintained constant. Alternatively the pulse length can be monitored. The pulse amplitude or mean pulse energy can also be monitored and maintained constant.