Abstract: Detector apparatus includes a diffraction grating (11) having a period such that the incidence of coherent point-source radiation upon it produces a number of spaced self-images of the grating behind it. A Moire grating (12) is placed to coincide with one of these self-images and a detector array (13-16) is placed behind the Moire grating to detect the resulting interference fringes.

Abstract: A pixel data memory is provided for use with an information display system having a raster scan screen divided into a plurality of pixels each of which represents a separate area of the screen. The memory comprises a multiple-bit memory plane (13) capable of providing a plurality of separate bit locations each of which may correspond to a separate display pixel and arranged to store pixel data in the form of a plurality of multiple-bit words. The memory plane (13) comprises a number of memory chips each capable of storing a separate bit of each of the multiple-bit words. An address generator (10) is operable to generate the addresses of required individual bit locations in the memory plane. A number of separate control circuits (14) are provided, equal to the number of bits in each word. Each control circuit (14) is associated with a separate memory chip and is responsive to a generated address defining a bit location on that chip to access the pixel data identified by the bit at that location.

Abstract: A laser optical cavity extends between two end reflectors (11, 12) and is defined by at least three sections. A number of folding reflectors (14) are provided for directing radiation emerging from one section into the next. An active medium is contained in the sections and excitation means are provided to produce laser action. A rigid support member (10) supports the end reflectors (11, 12) and the folding reflectors (14) around a generally cylindrical surface such that a continuous optical path extends between the end reflectors (11, 12) by way of each folding reflector (14) in turn. At least three of the laser sections extend across a substantial part of the area with the cylinder (10) and each section crosses at least one other section at or near to the axis of said cylinder as viewed along that axis.

Abstract: The apparatus comprises a radiation-sensitive detector (17) and optical means for directing radiation from an observed field of view on to the detector. The optical means includes a rotatable support member (10) rotatable about an axis (11) and carrying a number of reflecting members (12) equally-spaced around it. Each reflecting member (12) is located in a plane parallel to the axis (11) of the support member and each is arranged at the same non-perpendicular angle to a radius of the support member. A pivoted reflecting member (14) is located inside the locus of the plurality of reflecting members (12) and is rotatable about an axis (15) located in a plane perpendicular to that axis (15). In operation radiation from the field of view is reflected by the pivoted reflecting member (14) on to successive ones of the rotating reflecting members (12) and thence on to the detector (17).

Abstract: The apparatus includes alignment means (13, 14) for determining the direction of a sight-line (12) extending from an observer (11) to a display surface (10), projection means (15, 16) for projecting an image of a graticule into the sight-line for movement therewith, and control means (17) operable to cause the display of a movable cursor on the display surface (10) when the sight-line (12) intersects the display surface.

Abstract: A CRT display system providing a raster pattern, possibly for a flat screen CRT, has an oscillator driving a Line counter. The Line counter drives a Field counter and a Line DAC. The Field counter drives a Field DAC. In response, there are generated signals, representing functions, to be applied to the CRT deflection plates, and whereby there is represented the inverse of any function representing distortion of the raster pattern required to be corrected. At least one further DAC may be provided, comprising one of a pair of interacting DAC's, with one DAC driven by the Line counter, and one DAC driven by the Field counter, the output of said further DAC causing a combined function to be represented by the output of said other DAC. Said other DAC may comprise either the Line DAC, or the Field DAC; or said further DAC of another pair of interacting DAC's.

Abstract: The apparatus comprises a sighting unit, such as helmet 10 carrying a cathode-ray tube 11 and a semi-reflecting screen 13 enabling a user to view a display superimposed on an outside scene. The sighting unit carries a detector unit 15 which determines the movements of the helmet 10 without reference to apparatus external to the helmet, and preferably comprising some form of gyroscopic apparatus. The helmet also carries a boresight detector 16 which forms part of correction means operable to correct automatically from time to time for errors in the output of the detector unit.

Abstract: The apparatus permits an external target to be viewed along a sight-line by a sensing device and for the projection of a beam of laser radiation (12) towards the target. The apparatus includes a viewing window (10) transparent to radiation at a wavelength to which the sensing device is sensitive and inclined at an angle to the sight-line. The window (10) has a viewing area through which the target may be viewed and a laser output area through which the laser beam passes. An anti-reflection coating is formed on that surface of the viewing window (10) remote from the target. Optical deflector means (16) are provided for deflecting laser radiation reflected from the other surface of the viewing window in the laser output area into the viewing area of the window for reflection into the field of view of the sensing device.

Abstract: Apparatus for determining the position of a point movable throughout a measuring volume relative to a set of reference axes includes a probe member (10) having a probe tip (11) defining the position of the movable point. The measuring probe (10) also has first and second reference points (12, 13) spaced apart from one another and having a fixed known spatial relationship with one another and with the probe tip (11). Means (16) are provided for moving the probe member (10) so that the probe tip may be positioned at any desired point within the measuring volume. At least three distance measuring equipments (15) are provided, located outside the measuring volume at fixed known positions relative to the set of reference axes and each operable to determine the distance between it and each of the reference points (12, 13) on the probe member (10). Calculating means (19) are provided to calculate from said distance measurements the position of the probe tip (11).

Abstract: A radiation path directing system, such as sighting means 10, (FIG. 1) has an imaging detector (not shown) below the apparatus has a field of view centered on a sightline deflected from the vertical axis 22 by mirror 12 rotatable in elevation about axis 13 in yoke 14 and directed in azimuth by rotation of the yoke about orthogonal azimuth axis 22. To enable rapid changes in sightline azimuth and/or if the yoke assembly has a limited extend of rotation the mirror 12 can be flipped about axis 13 to divert the sightline azimuth by 180.degree. insteads of moving the complete (and possibly heavy) yoke assembly. In one simple construction a yoke rotation of .+-.90.degree. and mirror flipping enables a 360.degree. sightline to be described. Preferably conditions are defined relating current yoke position and demanded sightline azimuth (FIG. 5) to determine whether the sightline is achieved by yoke rotation with or without mirror flipping.

Abstract: Testing the transfer function linearity of analogue input circuits. The transfer function linearity of an analogue input circuit, such as an analogue-to-digital converter (ADC) 25 is tested by generating two consistently reproducible digital test signals (5), converting the digital test signals to analogue form (7) and forming a combination test signal as the average of the two `simple` test signals (16). On three successive occasions the digital test signals are generated and on each occasion a different one of the analogue signals is applied to the ADC under test and the digitized signals stored. A digital combination signal is formed by sampling the digitized `simple` signals and taking the average of the signals, the digital combination and digitized combination signals being subtracted for each sample and any discrepancies summed. The summed total after all the sample points comprising the test signal have been taken gives a measure of any non-linearity of the ADC.

Abstract: Apparatus for detaching helmet-mounted equipment (6) from the helmet (4) of a vehicle-mounted user (1) includes a quick-release fastening (8) securing the equipment to the helmet. A removal cord (11) passes from the equipment by way of a guide (10) and is attached to the vehicle (12). The action of the apparatus is to remove the equipment from the helmet to a position of safety when the user has to leave the vehicle in an emergency.

Abstract: A method is provided for extending the field of view of a head-up display includes a combiner (31) through which a scene may be viewed by an observer (10), and a display unit (14) having a display surface 13 from which light is directed by a collimating lens (17) on to the combiner. The method involves using combiner which comprises a thick phase holographic optical element extending between the limits of the total field of view in the elevation direction and having a fringe pattern formed therein. The pattern is in the form of parallel fringes 32 and the combiner is disposed so that the fringes extend perpendicular to the elevation direction and are aligned perpendicular to the plane bisecting the angle of intersection of the light-line (11) and the optical axis (16) of the collimating lens (17).

Abstract: A motor 12 (FIG. 2) is controlled to move at a demanded velocity, input at 29, by sampling the position of the motor at sample intervals, digitally determining the demanded change in position per sample interval, modifying each position sample by the addition of said demanded change, comparing the modified position value with the previous modified sample to derive a position error signal representing the position error between the instantaneous position and that demanded by motion at the demanded velocity, and applying the position error signals from successive sample intervals to motor drive means.

Abstract: Digital data storage apparatus includes a data store DS having a plurality of multiple-bit word locations, and validity store VS having a lesser plurality of multiple-bit word locations arranged such that each separate bit corresponds to a separate word location in the data store. A first auxiliary store AS1 has a number of bit locations at least equal to the number of word locations in the validity store with each bit identifying the status of the validity bits in a separate word of the validity store. A number of further auxiliary stores are also provided, arranged in increasing order of significance and each having a lesser plurality of bit locations each of which corresponds to a separate word location in the next less significant auxiliary store. Circuit means CM are provided and connected in such a way that areas of the data store may be declared valid or invalid by setting appropriate bits in each of the auxiliary stores. Any area of the data store may be declared invalid in not more than two cycles.

Abstract: Reaction force compensation means 70 (FIG. 1) for countering the reaction torque of a heavy body, such as rotatable yoke assembly 20, when accelerated relative to flimsily supported body 21 about axis 22, comprises a reaction member 71 rotatable about the, or a parallel, axis 22 and a reaction drive motor 74 coupled to rotate the reaction member by way of velocity step-down gearing 75. In response to acceleration of the body 21 the reaction drive motor 74 accelerates member 71 in the opposite direction producing an equal and opposite reaction torque on the structure. The reaction member is made with a higher moment of inertia about axis 22 than the body and is accelerated at a correspondingly lower rate to give the balancing reaction torque while requiring a smaller mechanical power input than might be expected. The power required of the drive motor is minimized by optimizing the gearing ratio having regard to the moments of inertia of the reaction member and drive motor.

Abstract: A bipolar transistor logic circuit has a hierarchical arrangement of pairs of bipolar transistors, each pair of transistors having their emitters connected together, and the bases of at least some pairs receiving a differential input to the logic circuit. The highest level has only one pair of transistors, with their emitters connected to a constant current source. A differential output is provided on two lines, at least the collectors of the lowest level being coupled selectively to the lines. The arrangement is required to be symmetrical. In an otherwise non-symmetrical arrangement, the arrangement is made symmetrical by including dummy pairs of transistors not receiving a differential input. In performing a logical operation, the differential output, and the collector potentials of each pair of transistors start to vary in the appropriate sense.

Abstract: A chirp signal generator circuit includes a pulse generator PG for generating a single impulse for application to first surface acoustic wave device SAW. This device produces an output signal comprising several cycles of energy at a predetermined frequency. A threshold circuit TH passes only that part of the output signal which second surface acoustic wave device EXP having the predetermined frequency as its center frequency, and this output signal is then amplified. The second device EXP generates a frequency modulated chirp signal.

Abstract: A system for providing a view of a scene scanned by an electro-optic framing sensor (30) includes control means (36) operable to cause the sensor to scan the scene in a number of frames each of which is viewed at a different viewing angle. Pickoff means (37) provide signals representing that viewing angle. Storage means (32) are provided to store the image information derived from each frame. Circuit means (33) are provided to transform the image information in each store (32) so as to remove distortions due to the different viewing angles, and the transformed image information is stored in a picture store (34). The contents of the picture store represent a view of the scene as viewed from a predetermined viewing angle.

Abstract: Measuring apparatus for determining the position of a point in a measuring volume relative to a datum point at which three mutually perpendicular axes intersect, includes a probe member supported for movement within that volume. Errors due to rotations about the various axes are corrected by providing additional transducers on each axis, there being (n+1) transducers where n is the number of rotations for which correction is required. The embodiments described have three X-axis transducers X.sub.1, X.sub.2 and X.sub.3 and three Y-axis transducers Y.sub.1, Y.sub.2 and Y.sub.3 which, with the appropriate circuitry correct for pitch and yaw errors about the two axes. For the Z-axis only two transducers, Z.sub.1 and Z.sub.2, are required. The circuit means combines the various transducer outputs to derive corrected values of the three co-ordinates.