Abstract: A modem for a digital data transmission system in which binary-coded data at up to 9.6 Kbit/sec is transmitted over a telephone line pair circuit, as phase and amplitude modulation (QAM) of a carrier signal at a frequency of 1800 Hz, at a line symbol rate of 2400 bauds. The modem utilizes two data signal processors (4 and 5) and two gate arrays (6 and 7), controlled by a microprocessor (8), to carry out digitally all the processes required to convert binary coded data signals into PCM coded samples of the required carrier signal for transmission and to recover binary coded data signals from PCM coded samples of a received carrier signal.

Abstract: A transaction system enables a portable token to co-operate with a fixed terminal. The token is inductively coupled to the terminal, and receives data from the terminal via a frequency modulated carrier signal. Data is sent from the token to the terminal by amplitude modulation of the carrier signal from the terminal, i.e. by modulating the power drawn by the token from the terminal. The power needed to energize the on-board processing capability of the token is also obtained from the terminal via the inductive coupling. The token includes an arrangement for commencing processor operation in an orderly manner when it is brought into the proximity of a terminal, and for providing an orderly shut down when the token is withdrawn.

Abstract: An analogue-to-digital converter in accordance with the invention comprises a feed-forward arrangement in which, in a first stage, the analogue input signal is applied via a filter to a subtractor along a first path and is applied via a second path to an analogue-to-digital converter followed by a digital filter and then converted back into analogue form to be applied via a bandpass filter to the subtractor. The output of the subtractor is therefore an error signal representative of the difference between the analogue input signal and the predicted signal in analogue form. The error signal is applied to an analogue-to-digital converter and is combined with the predicted signal in digital form taken from the output of the digital filter via another filter to produce the digital output signal. Control means are provided to provide phase and gain matching between different parts of the circuit.

Abstract: In a process for manufacturing a thin film transistor, a first polysilicon layer is formed on a substrate and a silicon dioxide layer is formed on a region of the first polysilicon layer leaving exposed regions of that layer. A second polysilicon layer is formed on the silicon dioxide layer and aligned therewith. Regions of a selectively-grown electrically-conductive film are deposited on the second polysilicon layer and on the exposed regions of the first polysilicon layer, the film being such that it wil not grow on the edges of the silicon dioxide layer, but will grow on the exposed polysilicon to form gate, source and drain electrodes. The edges of the silicon dioxide layer therefore remain uncoated. The film may be formed of tungsten or may be formed, for example, by selective silicon epitaxy, phosphorus doped.

Abstract: Synthetic aperture radar is a known system for producing a high resolution image of the terrain under a moving platform, in which the effect of a large antenna (which would give high resolution in the direction of travel (azimuth direction)) is synthesized by processing together with suitable phase shifts a large number of radar returns from a smaller antenna for which the footprints overlap.In order to simplify the image processing task, which is preferably carried out at high speed and on the moving platform itself, according to the invention an azimuth processor comprises a plurality of data processing modules 35.sup.1 -35.sup.R/N, each associated with a different part of the (range line) samples of echo returns, for example, by virtue of being connected to successive sections 33.sup.1 -33.sup.R/N of a shift register into which successive range lines are clocked. Each module 35.sup.i includes a memory 39.sup.i to store the sets of range line samples, a processing section 37.sup.

Abstract: An active noise control system for reducing the amount of noise propagated along a duct comprises a microphone mounted in the wall of the duct for detecting the noise, and an active antiphase noise source, such as a loudspeaker, which is mounted substantially in the center of the cross-section of the duct. A control circuit coupled between the microphone and the antiphase noise source includes an integrator having a specific transfer function, which improves the loop gain of the microphone/source loop at low frequencies, and secures stability by altering the phase.

Abstract: A beam forming network employing a matrix of resistive coupling elements to link individual elements E.sub.1 to E.sub.n of an antenna to the different phase terminals 3, 4, 5 and 6 of a phase combiner. Because of unwanted coupling between the conductive members forming the matrix it has in some circumstances been found impossible to select values of the coupling elements to give a required beam pattern. The invention solves the problem by including phase shifters in alternate lines to the antenna elements. A separate matrix and phase combiner is provided for each beam to be formed.

Abstract: A method of testing thermal imagers includes heating selected portions of a quantity of a smectic liquid crystal material (9) with a laser (25) such that the material in the selected portions changes from a homeotropic texture in which it is transparent to incident infrared radiation to a focal conic texture in which it scatters incident infrared radiation. An infrared source (27) is arranged to direct infrared radiation onto the quantity (9) so as to read the pattern of selected portions across the quantity.

Abstract: An automated vehicle includes a navigation system which carries out a dead reckoning calculation of the vehicle's position based on inputs from sensors on the motion of a steering wheel in the preceding time interval, .DELTA.t. Parameters of the system including the heading angle, the spatial position x,y the angular drift in the steering angle .alpha., a crabbing angle .beta. and a variation 1.sub.dm in steering wheel radius are updated by the addition of the product of a Kalman gain calculated by computer and an error signal produced each time an observation is made by laser bearing finding equipment on the vehicle.

Abstract: A transaction system enables a portable token to co-operate with a fixed terminal. The token is inductively coupled to the terminal, and receives data from the terminal via a frequency modulated carrier signal. Data is sent from the token to the terminal by amplitude modulation of the carrier signal from the terminal, i.e. by modulating the power driven by the token from the terminal. The power needed to energize the on-board processing capability of the token is also obtained from the terminal via the inductive coupling. The token includes an arrangement for commencing processor operation in an orderly manner when it is brought into the proximity of the terminal, and for providing an orderly shut down when the token is withdrawn.

Abstract: Pleochroic fluorescent dyes of the general formula I: ##STR1## in which R is hydrogen or an aliphatic hydrocarbon radical containing not more than 20 carbon atoms and --CH.sub.2 -- between carbon atoms or adjacent to the bicyclo[2.2]octane residue may be replaced by --O-- may be dissolved in liquid crystal host material to form displays which are caused to fluoresce by incident low-energy ultraviolet initially absorbed by the liquid cyrstal host material and then internally transferred to the fluorophor. These dyes have greater stability to ultraviolet than other perylenedicarboxylic diesters while possessing good fluorescent properties and satisfactory order parameters. In formula I, R is preferably a straight or branched alkyl, and/or cycloalkyl group having 3 to 10 carbon atoms, preferably 5 to 7 carbon atoms. The liquid cyrstal host material preferably contains an energy-transfer agent such as a 4-substituted 4"-cyanoterphenyl. The 4-pentyl- and 4-propyl- bicyclo[2.2.

Abstract: A display device is described which comprises a liquid crystal host material and an anisotropically emitting fluorescent guest material dissolved in the host material such that the molecules of the guest material align with the molecules of the host material. An electric field applied across the host material causes the direction of radiation emitted by the guest material incident on an interface between two materials of different refractive index to vary so as to control the amount of radiation emitted by the display.

Abstract: A security arrangement includes a token in the form of a thin lamina which co-operates with a receptor. The token includes an optically readable pattern in the form of a bar code, and a thin film holographic reflector which deflects the light which is modified by the bar code onto an optical sensor. The optical sensor is positioned such that the light will not reach it in the absence of a holographic reflector.

Abstract: An optical device for use in forming a holographic record, comprising a polarizing beam splitter and a spatial light modulator arranged to derive from an incident beam a focussed image beam and a collimated reference beam, the device being of unitary construction and providing substantially equal path-lengths for the image and reference beams.

Abstract: A stabilised mount (e.g. for an antenna) has two gyroscopic rotors mounted in such a way that they can pivot about orthogonal axes. Rewinding of the antenna (to avoid undue twisting of the electrical cables) is liable to cause a voilent destabilisation of the mount because of the gyroscopic action of the rotors. To prevent this destabilisation the rotors are locked against the aforementioned pivoting action during the rewinding procedure.

Abstract: An electro-optic display comprises a two dimensional array of liquid crystal cells (C11A,B to C44A,B) each switchable by means of electrical signals applied to respective pairs of address lines connected to the cell by respective transistors (T11-T44). Each main electrode of each transistor is isolated from the rest of the array by a respective cell of the array.

Abstract: A liquid crystal device comprises a ferroelectric smectic phase liquid crystal enclosed between two surfaces, the surfaces being such that the directors of the liquid crystal adjacent the surfaces are not parallel to the surfaces. The directors adjacent one of the surfaces are not parallel to the directors adjacent the other surface, the liquid crystal cone angle being equal to half the angle between a pair of directors each adjacent a different one of the surfaces.

Abstract: An earth terminal for a satellite communication system incorporates an oval or eliptical shaped antenna 1 whose horizontal dimension d.sub.1 is greater than it's vertical dimension d.sub.2. The relatively small dimension d.sub.2 allows the antenna to be transported by road while at the same time giving a beam shape which is broader in elevation than in azimuth. This special beam shape gives certain advantages which are described in the specification.

Abstract: An electrical circuit arrangement includes a conductive link through an insulating layer separating two conductive layers. This link is formed by placing an evaporable plug on a first conductive layer, forming the insulating layer around it and then vaporising the plug. The resulting gap is then infilled with conductive material and a second conductive layer formed on the insulating layer.

Abstract: A vacuum valve device comprises a substrate on which is formed an updoped silicon layer from which a silicon dioxide layer is grown. First, second and third electrode structures are formed on the silicon dioxide layer by depositing a metallic layer and etching away unwanted portions of the layer. The first electrode structure has a pointed end and/or a sharp edge and/or is formed of low work function material so that, when a suitable voltage is applied between the first and third electrode structures, electrons are emitted from the first electrode structure due to a field emission process. Electrons therefore flow from the first to the third electrode structure substantially parallel to the substrate. The second electrode structure acts as a control electrode.