Abstract: Apparatus (FIG. 1), for training in the rapid and accurate reaction to a situation confronting one or more trainees 12, 12' in an enclosed room 11, has one wall thereof formed by a screen portion 14 onto which an optical image is back-projected by projector 16. Each trainee's weapon 22 has a light emitter 24 responsive to firing the gun (containing blanks) at the screen to simulate the projectile impact point by spot 26. A television camera adjacent the projector and viewing the rear of the screen receives the spot and relates the position of this within the camera field to datum points of the projected image, the datum points 36' being visible to the camera and not the trainee.

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: Power supply apparatus for a gas laser discharge tube (10) having anode and cathode electrodes (11 and 12) comprises a first power supply (13) operable to satisfy the running power requirements of the discharge tube. A second power supply (16) is also provided and is operable to generate a voltage which, when connected in series with the output of the first power supply (13) causes the initiation of a discharge in the discharge tube (10). A spark gap (17) is operable to connect the outputs of the two power supplies in series with one another when the discharge is to be initiated.

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 divider is made from a layer (1) of conducting material carried on an insulating support (2). A first slotline (3) is formed in the conducting layer extending from a first input port (A). A second slotline (5, 6, 7) is formed at right-angles to and spaced from the end of the first slotline (3), extending between first and second output ports (C and D). Third and fourth slotlines (8, 9) extend from the end of the first slotline (3) to points on the second slotline spaced by a distance which is electrically short compared with one-quarter of a wavelength. The third and fourth slotlines (8, 9) are an odd multiple of quarter-wavelengths long. A resistor (10) is connected across the second slotline substantially midway between the ends of the third and fourth slotlines, and has a resistance such that the output ports are correctly terminated.

Abstract: In known sightline stabilizing apparatus 10 (FIG. 1) a gyro-stabilized reflector 25 maintained in orientation in space about two axes 18 and 26 by gyro means in the mechanism 22. The reflector mechanism is contained in housing 17 and is pivotable about elevation axis 18 in relation thereto. The housing also carries a sensor, e.g. a tv camera providing signals to a remote (non-stabilized) image display device, and is itself rotatable in elevation relative to a platform 16 rotatable in azimuth. The apparatus is normally carried by a vehicle and movements thereof cause servo responses of the mechanism 22 to stabilize the mirror and follow-up movements of the housing and pedestal 16 restore the mirror to the center of its limited motion in the housing. However, changes in elevation angle of the reflector cause rotation of the remote image about the center of its field of view and motion induced changes can rapidly lead to motion sickness in an observer of the image.

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: A solid state imaging device (FIG. 2) includes an array 10 of photoelectric elements 11 on which an image is formed, and overcomes poor resolution due to insensitive areas 12 between elements by interposing between a focussing lens 13 and the array an optically transmissive member in the form of a rotatable disc 15 having parallel faced portions of different thickness 16, 17 which extend into the optical axis of the focussing means in turn and are inclined thereto to displace the image laterally on the array. The difference in thickness causes an image displacement equal to half of the element pitch and signals of each image displacement are stored in frame stores 21, 22 from which they may be read to provide the equivalent of a higher density array. Disc portions may be the same thickness but of different refractive indices or angles to the optical axis. A larger number of portions (FIG. 5) may be used to give more displacements.

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 servo system 10 (FIG. 1) for positioning a sighting mirror 11 connected to a pulley 16 comprises a drive motor 13 rigidly connected to a drive pulley 15 in turn coupled by a tensioned drive belt to the pulley 16. Angular position of the motor or pulley 15 is measured by sensor 18 and passed by way of phase advance network 19 and amplifier 21 to produce an error signal for the drive motor. The pulley 16 is outside of the servo loop and any oscillations induced in the tensioned belt at its resonant frequency, possibly originating from electrical noise in the servo loop, will be uncontrollable.

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 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 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: Gas laser apparatus comprises a cavity 10 containing a gaseous active medium, and discharge electrodes 11 and 12 between which a potential difference may be applied to produce an electric pumping discharge in the active medium. A reservoir 17 communicates with the cavity to form a sealed enclosure containing the active medium and volume control means 19 are contained in the reservoir 17 to vary the pressure of the gaseous active medium in the cavity.

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.

Abstract: In a radiation-utilizing measurement system including a rotatable reflector, a point source, and a point detector, there being a plane both at right angles to the rotational axis and including the source and the detector, the plane also including the optic axis of the system extending equidistant between the source and the detector, and there being a plane including the rotational axis and the optic axis, there is provided a refracting element with zero power in the first plane, and a finite positive power in the second plane; or, at least the equivalent of, two refracting elements, the second refracting element having zero power in the second plane, and a finite positive power in the first plane. Thereby, respectively, the effects caused by reflector fluctuation; and also the effects caused by reflector rotation, when the source provides a conically divergent beam of radiation; are obviated.

Abstract: A gating arrangement for a pulse compression circuit includes a surface acoustic wave delay line SAW responsive to an input pulse to generate a frequency-modulated radio-frequency output signal which is applied to an output gate OG. The output signal is also applied to circuit means DC operable to product a digital pulse corresponding to each cycle of the output signal. The pulses are counted by a counter CT and applied to control means CM. This responds to first and second predetermined counter states to control the operation of the output gate OG.