Abstract: Navigation apparatus in accordance with the invention uses a Large Reference/Small Scene approach in which a plurality of small scene areas are obtained by viewing the surroundings of a moving object and are compared together with a large reference area to produce a match between them, and hence give an indication of the position of the object with respect to the reference area. The apparatus utilises the fact that the small scene areas are in a known distribution and correlation maxima should be found having that distribution, other maxima being effectively randomly distributed.

Abstract: A correlation processor arrangement is used to guide an airborne vehicle along a path precisely to a predetermined destination. Guidance is divided into three distinct phases, and during each phase the position of the vehicle is verified by matching the view of its surroundings with stored reference data representing the expected fields of view. During the first navigation phase the stored data consists of predetermined terrain areas. During the second detection phase the destination is acquired, and during the third homing phase the view of the approaching destination is used as the stored reference data.

Abstract: In a noise radar a pseudo-random sequence is generated repeatedly and used to phase modulate a transmitted signal. The transmission is interrupted during a number of periods during each pseudo-random sequence which allows returns from targets to be received from the same antenna as is used for transmission during those periods of interruption. Each transmitted pulse, between successive periods of interruption, contains a different selection of successive digits of the code thus increasing the apparent randomness of the transmitted code and making detection more difficult.

Abstract: In order to identify a target a data base is compiled containing records, for each of different known types of object, each record being derived from successive range sweeps of the object as seen from different angles and containing information defining the relative positions of different points of reflection on the object. In order to identify an unidentified object, information from at least one range sweep across it (and preferably a number of such range sweeps taken when viewing the object from different angles) is compared with similar information recorded in the data base to ascertain whether the unidentified object belongs to one of the known types.

Abstract: A median filter includes a number of identical modules each arranged simultaneously to receive the current value of an imcoming digital signal. Each module includes a feedback shift register of special design enabling it to be set to receive its input to any one of its stages. The shift registers of the different modules are set to receive their inputs at different stages and logic means is associated with each shift register for comparing the content of one stage with the contents of each other stage to determine whether the content of that said one stage is the medium value. If it is the median value it is passed to an output of the circuit.

Abstract: A method of producing a reflection hologram wherein light from a source (29) is directed onto the hologram recording medium (23) via a lens (21) which causes light reaching the medium (23) to pass through a construction point (33). The light beam is arranged where it is incident on the lens (21) to be of small cross-sectional area compared with the lens aperture and is arranged to scan over the lens aperture so that the beam scans the medium (23) in a regular pattern of overlapping narrow bands. In this way the hologram may be made to have uniform spectral properties despite a non-uniform energy distribution in the beam.

Abstract: A data processing arrangement is operative to combine data representing different kinds of information from disparate sources. The data is stored under assigned addresses having a mutually compatible co-ordinate format, and is processed using those addresses. Relevant portions of data from a very large amount of information can be readily extracted in this way, and combined with other data which is related by virtue of a common address. The arrangement is applicable to flight management of an aircraft.

Abstract: An electric circuit testing equipment wherein signals are picked up from a selected point in the circuit by a probe unit (41) capacitively coupled to the selected point and the signals picked up by the probe unit are conditioned by circuits (47 to 61) which produce an output signal corresponding only to signals picked up by the unit from the selected point. The use of a capacitively coupled probe unit reduces the possibility of the unit affecting the operation of the circuit under test while the conditioning of the picked up signals enables the pick-up of unwanted signals to be tolerated. Designs of probe unit to minimize pick-up of unwanted signals are also described.

Abstract: Bias current to an array of detectors is switched off during periods when the detectors are fruitlessly receiving energy from inside the image housing to either side of an optical aperture thereof. This reduces the generation of heat in the detectors.

Abstract: A cathode ray tube (CRT) display arrangement including protection means for protecting the screen of the CRT (1) against excessive heating, by the electron beam, e.g. due to failure of the beam deflection drive circuits (5), the protection means comprising an electronic storage means (27 to 41) having storage locations in which are stored values indicative of the temperature at different locations on the CRT screen, and means (7) for controlling the electron beam current in dependence on the contents of the storage means.

Abstract: An apparatus for indicating the position of an object in a three dimensional space is described. The apparatus includes a video arrangement for producing a stereoscopic image of a scene including the object. Overlay generators superimpose on this image a stereoscopic image of a cursor. Cursor control means are provided for varying the apparent position of the cursor in the scene and for providing an output representing the apparent position of the cursor.

Abstract: An apparatus incorporating recursive estimators, more particularly apparatus for measuring the state of a dynamic system using a recursive estimator for modelling the dynamic behavior of the system, and navigation systems using a recursive estimator for navigation integration. Also disclosed are novel methods of updating the inputs to the estimators of such apparatus and systems.

Abstract: A multi-pin plug and socket electrical connector in which adjacent pins are sealed from each other at the interface by an elastomeric sheet. The sheet extends over the entire interface with each pin extending through a hole in the sheet. Each hole is surrounded by a O-ring integral with the sheet. The sheet may extend within each O-ring to make contact with the pin. The pins are sealed at their opposite, i.e. wire ends by individual elastomeric seals in the pin bores.

Abstract: A helmet mounted binocular goggle night vision viewing system comprising two independent night vision viewing arrangements, one for each eye of a wearer of the helmet, supported from above the face aperture of the helmet, each viewing arrangement comprising an optical projector arranged to project an intensified image of a scene ahead of the helmet wearer downwardly to a body of light refractive material in front of the wearer's eye having parallel flat fore and aft surfaces spanned by an upper surface via which light from the projector enters the body for reflection towards a curved partially reflective, partially transmissive surface within the body by which the light is reflected back towards the aft surface for transmission therethrough to the wearer's eye, thereby to provide the wearer with a view of the projected image superimposed on his view of the scene ahead through the body.

Abstract: A display head for a head-up display system for use in a confined space, such as a high performance aircraft cockpit. The display head has a first part (11, 13, 23, 25) adapted to be mounted on an overhead member and the remainder (15, 21, 28, 29, 31) of the display head is pivotally mounted on the first part so as to enable it to be moved readily between operative and stowed positions. In the stowed position the display head does not obstruct movement of the user's head or present an obstruction on which the user may strike his head.

Abstract: A vehicle night vision system comprising a headgear mounted night vision goggle 11 incorporating an image intensifier which produces an intensified image of a scene forward of the goggle superimposed on a user's direct view of the scene through the goggle wherein the intensity of the image produced by the intensifier is reduced when the user views a vehicle interior display via the goggle to prevent interference with the user's direct view of the display through the goggle.

Abstract: An intruder alarm system of the type used to detect mechanical vibrations in a security fence or the like. Vibrations are assessed for alarm potential by detecting peak amplitudes against a dynamic vibration reference. A sufficient ratio between the two indicates an intrusion.

Abstract: A display head (11) for a vehicle head-up display system wherein the display head combiner (35, 37) is pivotally supported by means of two kinematic chains (19, 21, 23, 23', 25, 25') so as to enable the combiner (35, 37) to be moved from an operative position to a stowed position in which the combiner (35, 37) together with its support means (19, 21, 23, 23', 25, 25') is inconspicuous.

Abstract: A linear high power amplifier suitable for low voltage operation comprising a push-pull output stage (Q1, Q2) arranged to control the voltage supplied to a load (Z.sub.L) in dependence on an input signal (V.sub.IN) applied to the amplifier. Means (L.sub.S, S) is provided for separately supplying to said load (.sub.Z L) a current (I.sub.S) which changes at a rate faster than the maximum rate of change of current (I.sub.L) in the load (Z.sub.L) required by the input signal (V.sub.IN) thereby to produce a corresponding change in the current (I.sub.A) required to be supplied by the output stage (Q1, Q2) to the load (Z.sub.L) in order to maintain the voltage across the load (Z.sub.L) at the value required by said input signal (V.sub.IN). Switching means (Q3, Q4, C) operated in dependence on the value of the current (I.sub.A) supplied to the load (Z.sub.L) by the output stage (Q1, Q2) causes the sense in which said changing current (I.sub.S) changes to reverse when said current (I.sub.

Abstract: An electric circuit module suitable for mounting in a rack, e.g. by sliding action, in parallel spaced relationship with other similar modules, comprising a shallow box (111) having two heat conductive parts (113 and 115) each comprising one major wall of the box. The electrical components (139) of the module are mounted on the interior major surfaces of the two box parts (113 and 115) and the two parts provide heat paths between the components (139) and external surface portions (133) of the box.