Abstract: An electrical filter network particularly suitable for use at microwave frequencies, comprises a main transmission path and a plurality of pairs of secondary paths interconnected by couplers which divide an incoming signal into components on the several paths and recombine the transmitted components to provide an output signal. Conditions are placed on the electrical lengths of the transmission paths; the magnitude of the frequency-independent components of phase change along the paths and the wave amplitudes in the paths.

Abstract: A method of coating a fibre in which a sleeve of polymer is extruded, fibre is fed into the sleeve as it is formed, and the diameter of the sleeve is reduced by a drawing process to produce a sleeve of polymer which loosely envelops the fibre. We also provide a fibre having a tubular sleeve of polymer, the sleeve having its molecules orientated to lie longitudinally with respect to the axis of the fibre. The sleeve has relative strength in a longitudinal plane and relative weakness in a transverse plane.

Abstract: Dielectric optical waveguides are joined using a length of tape. One end of the tape is formed into a loop and the ends of two optical waveguides to be joined inserted into opposite sides of the loop. The diameter of the loop is reduced to such an extent that the waveguides cannot be moved alongside one another. The ends of the waveguides are moved together and the loop drawn tightly around the waveguides and secured in position. The diameter of the loop can be reduced using a pair of juxtaposed rollers. The ends of the waveguides can be secured together by suitable adhesive.

Abstract: A telephone control console including visual indicator means, data input means, audio frequency input and output means, microprocessor means, data transmission and reception means wherein said microprocessor means controls at least some of said visual indicator means in accordance with data received by said data reception means and in accordance with data input through said data input means and also controls the transmission of data by said data transmission means in accordance with instructions from said data input means and wherein said audio frequency input and output means include an input and output for an operator's telephone.

Abstract: A dielectric optical waveguide joint in which first and second dielectric optical waveguides are located end to end in a groove in a plate of non-ductile material. The dielectric optical waveguides are retained in the groove by a mass of ductile material which has been formed so as to flow into intimate contact with the plate and the first and second waveguides. The invention also provides a method of forming a waveguide joint.

Abstract: A construction of an active filter having the same characteristics as a predetermined passive filter is described in which the capacitors of the passive filters are replaced by a topologically equivalent first network of resistors and the inductors of the passive network are replaced by a topologically equivalent second network of resistors, the two networks of the resistors being interconnected in a manner corresponding to the connections in the passive filter and connected to points corresponding to interconnection points of the passive filter by means of negative impedance converters, the converters connected to the first network having conversion ratios effective to convert resistance into negative capacitance and the converters connected to the second network having conversion ratios effective to convert resistance into negative inductance. The input and output to the active filter may be through similar negative impedance converters or may be directly to points in one or other resistive networks.

Abstract: Data processing equipment suitable for recording details of manually connected telephone calls has a plurality of operator stations with keyboards and VDU's connected in groups to operator's control units which respond to keyed instructions to obtain data from peripheral units storing such data and for recording on magnetic tape cartridge the details of the calls. Each operator's control unit is connected to eight operator stations but is capable of handling inputs from twelve such stations. In the event of breakdown of an operator's control units the eight stations allocated to it are divided into two groups of four which are transferred to the two control units adjacent to that which has broken down. Among the criteria used to determine whether a control unit has broken down are the filling of buffer stores and the failure to perform a particular operation within a predetermined interval of time following the previous performance of that operation.

Abstract: A method of error detection in a digital system in which at least one digit in every n (where n is an integer greater than two) is omitted from use as the "particular digit" in the comparison of succeeding particular digits in a received pattern with the combination in accordance with a predetermined function of at least two digits preceding the particular digit in question by a particular spacing. The pattern is a pseudo-random binary sequence of maximal length and every third digit is taken as the particular digit. Every digit forms part of a comparison whether as "particular digit" or as one of said "at least two digits preceding". Shift registers, means to divide digits between the shift registers, and modulo -2 adders are used to carry out the method.

Abstract: An arrangement for charging a rechargeable battery which has a plurality of sections. The battery can be selectively connected by a switch either to a source of charging current or to supply power to a load. When the battery is connected to the charging current source the sections are connected in parallel and when it is connected to a load the sections are connected in series.

Abstract: Equipment for draining and refilling the lubricating oil sump of a motor vehicle comprises a large capacity main oil reservoir. Inlet means to the reservoir from the sump include a vessel which is evacuated to suck oil from the sump and pressurized to cause the oil to flow into the reservoir. Oil rejuvenating means are included in the inlet. Means are provided for discharging a metered dose of oil back to the sump from the reservoir.

Abstract: A method of coating a fibre in which a sleeve of polymer is extruded, fibre is fed into the sleeve as it is formed, and the diameter of the sleeve is reduced by a drawing process to produce a sleeve of polymer which loosely envelops the fibre. We also provide a fibre having a tubular sleeve of polymer, the sleeve having its molecules orientated to lie longitudinally with respect to the axis of the fibre. The sleeve has relative strength in a longitudinal plane and relative weakness in a transverse plane.

Abstract: Apparatus for feeding flat items comprising a rotatable body, a drive member having a drive surface for drivingly contacting the surface of an item, said body and said member defining therebetween a nip, and respective surface portions of the body and the member at the nip being movable only in directions extending askew of one another with a skew angle such that the body surface portion frictionally resists the passage of an item through the nip.

Abstract: Apparatus in the form of a stencil, wet transfer material or dry transfer material is disclosed for marking characters on a surface. A set of character-defining indicia are provided on the stencil or transfer material and symbols having simple geometrical shapes are also provided to enable visually harmonious character spacing to be achieved. Some or all of the indicia have two or more spatially separated symbols so that character spacing can be related to the particular character pair combination being drawn or marked. Simple rules are provided for matching symbols to each other.

Abstract: A launcher for waves of selected mode in an optical dielectric waveguide having a core surrounded by cladding, in which the launcher includes a prism of refractive index greater than that of the waveguide and preferably greater than that of the core of the waveguide which is placed against the waveguide either before or alongside an outwardly tapering portion of the waveguide. Light from a laser is directed through the prism on to the waveguide to induce the waves in the waveguide. A matching fluid, which may set to a solid, improved the coupling of the prism to the waveguide. A detector of similar construction is also described, the tapering of the waveguide being inward.

Abstract: A signal level stabilizer includes two amplifier stages, each stage having a respective feed-back loop to control its gain. The gains of the amplifiers are varied in response to variations in the level of the input signal to give a substantially constant output signal. At low levels of the input signal the gain of one of the amplifiers only is varied in response to variations of the input signal and at high levels of the input signal the gain of the other amplifier is varied. The amplifiers may be part of a repeater in an optical communications linkage and one of the amplifiers may then be a photodiode and the other a power amplifier.

Abstract: Drive circuits for a flat panel display using a matrix of DC responsive phosphor dots are disclosed. Enabled row conductors receive a pulse of DC potential equal to +HV, whereas disabled row conductors receive +HV/.sub.2. Enabled column conductors receive zero potential, whereas disabled column conductors receive +HV/.sub.2. HV is in the range 90 to 140V. This allows semiconductor integrated circuit display drivers to be used in conjunction with the column conductors. Discrete transistor complementary-pair drivers are used for the row conductors. Scanning and character generation functions are achieved by the use of semiconductor integrated circuits. A pulse-width brightness control operates by selection of one of several logical combinations of the outputs of a counter. Two or four column driver circuits are provided to simplify high density connection problems and a divider circuit causes the column driver circuits to be addressed in sequence.

Abstract: A device for severing a dielectric optical waveguide comprising knife means, means for clamping a dielectric optical waveguide in closely spaced relationship with said knife means and an anvil which is movable towards said knife means. The anvil is so arranged and constructed that, in use, as it moves towards the knife means, it engages a dielectric optical waveguide clamped by said clamping means and urges it towards the knife means. When the waveguide comes into contact with the knife means it is under a given stress and has a predetermined configuration. The device also includes means for effecting movement of the anvil.

Abstract: Data processing equipment suitable for recording details of manually connected telephone calls has a plurality of operator stations with keyboards and VDU's connected in groups to operator's control units which respond to keyed instructions to obtain data from peripheral units storing such data and for recording on magnetic tape cartridge the details of the calls. The magnetic tape cartridge recording units are duplicated and the data to be recorded in the two units, which are separately generated and should be the same, are compared with one another and their validity checked. If both data are valid, whether they differ or not, they are recorded. If only one set of data is valid only the valid data are recorded by both recorders. A marker signal may be recorded to indicate that the data recorded may be incorrect.

Abstract: A method and apparatus for testing for forward echoes produced by signal transmission through a length of transmission line in which a succession of 1 ns pulses are applied to the line and the outward signals are multiplied by pulses delayed by a succession of discrete delay times. The products resulting from 65,500 pulses subjected to the same delay are integrated to eliminate the effects of thermal noise and the results for different delay times plotted against the delay time to produce a correlation curve in which the echoes appear as perturbations on the curve.

Abstract: A method of growing semiconductor compounds which are formed from elements of group III with elements of group V by liquid phase epitaxy. A suitable solvent is provided in contact with a source of the compound to be grown, the solution is heated to a predetermined temperature and the solute is allowed to come to equilibrium with the solvent. The solution is then subjected to a rapid, relatively small decrease in temperature to produce supersaturation of the solution. The temperature is then maintained substantially constant and, after a predetermined first period of time at the constant temperature, the solution is brought into contact with a substrate on which the compound is to be grown for a predetermined second period of time.