Abstract: A mixer receives a frequency shift keyed (FSK) radio signal having two transmission frequencies and mixes the radio signal with a first or a second local oscillator signal from a local oscillator to provide a mixed signal. The mixed signal lies within a high or low band of frequencies depending upon the frequency of the FSK signal and upon the local oscillator signal received by the mixer. A detector receives the mixed signal and detects in which band of frequencies the mixed signal lies, and generates a switching signal in dependence upon the band of frequencies in which the mixed signal lies. If the FSK signal changes to a different transmission frequency and this causes the mixed signal to lie in the low band of frequencies, then a switching signal is generated which switches the local oscillator such that the oscillator generates a different local oscillator signal which causes the mixed signal to shift to the high band of frequencies.

Abstract: A fuel monitoring system comprises a centrifugal air separation chamber having input and output Venturi devices. The system is arranged so that fuel from the fuel tank of the aircraft is pumped to the input Venturi device which due to the pressure drop therein, serves to release air from the fuel before it passes into the centrifugal air separation chamber where the air released from the fuel is separated out and exhausted from the chamber, whereas the substantially de-aerated fuel passes from the separation chamber into the output Venturi device, which produces a pressure drop enabling the vapor pressure of the de-aerated fuel to be determined therefrom.

Abstract: The invention relates to a monolithic light detector or generator integratd with an amplifier. The amplifier includes an F.E.T. comprising a substrate on which are formed source and drain contact layers separated by a groove. The gate layer is formed in the groove bridging the source and drain layers, and the optical system comprises additional layers formed on the substrate or formed on top of the gate layer with suitable conductive connections between the two.

Abstract: A quick release electrical connector comprises a plug part and a socket part. The socket part has an external screw thread and a coupling sleeve is captive on the plug part. Connected to the plug part is a number of internally screw threaded portions which are adapted to engage the screw thread on the socket part. The coupling sleeve has a surrounding axially movable retaining sleeve which in one position retains the screw threaded portions in engagement with the socket screw thread. In another position the retaining sleeve allows the screw threaded portions to move radially outwards out of engagement with the socket screw thread allowing quick separation of the plug and the socket part.The connector includes a thrust washer to prevent relative rotation between the plug and the coupling sleeve in the event of vibrations causing inadvertent unscrewing of the socket part.

Abstract: A signal strength detector comprises first, second and third transistors of the same conductivity type. The emitter electrodes of each transistor are connected together and coupled with one of a pair of dc supply lines. The collector electrodes of the first and second transistors are each coupled with the other of the pair of dc supply lines. The base electrode of the first and second transistors are each coupled via a resistor to the base electrode of the third transistor. The collector electrode of the third transistor is effective to provide a source of output current which is representative of a differential signal level between the base electrodes of the first and second transistors.

Abstract: The plastic encapsulation material covering an integrated circuit is impregnated with a corrosion inhibitor evenly dispensed throughout the material. This inhibits the corrosion of the metallization on the surface of the integrated circuit thus prolonging the life of the device particularly under adverse environmental conditions.

Abstract: An FM detection apparatus comprising a frequency dividing means, having a division ratio N, arranged to receive an incoming radio frequency (RF) signal carrying frequency modulation and to frequency divide the RF signal to provide a plurality of frequency divided signals each at the same frequency but mutually phase displaced so that the RF signal is represented by the divided signals in combination, a plurality of FM detectors arranged so that each FM detector receives a different one of the frequency divided signals and provides an output signal corresponding to the frequency modulation carried by the received frequency divided signal, and adding means operative to combine the output signals to provide a demodulated signal corresponding to the modulation carried by the incoming RF signal.

Abstract: A frequency modulation detection arrangement comprises an FM detector and an injection-locked frequency divider arranged for receiving a radio signal and for providing a frequency divided radio signal in response thereto. The FM detector is coupled with the injection-locked frequency divider for receiving the frequency divided radio signal therefrom and for producing a signal indicative of the information content of the modulating wave of the radio signal.

Abstract: An FM detector comprises a frequency divider arranged to frequency divide an input FM signal and a phase sensitive detector coupled to the frequency divider. The detector receives a first frequency divided signal from a first path and receives a second frequency divided signal from a second path. The second path has a phase shift means located therein which is operative to shift the phase of the second frequency divided signal, in dependence on its frequency, relative to the phase of the first frequency divided signal. The phase sensitive detector provides an output signal corresponding to the modulation carried by the input signal.

Abstract: Small lengths of conductors, cut to the appropriate size are used as radar "chaff" or passive reflectors to give spurious returns on an enemy radar and thereby act as an electronic countermeasure. Currently used chaff includes chopped aluminum foil, aluminum coated glass fibres and silver coated nylon monofilaments. Current radars operate in the 10.sup.10 Hz region and current chaff dipoles are of centimetric size, but future radar systems are likely to operate at higher frequencies requiring shorter dipoles lengths to achieve an increased packing density the dipoles also need to be thinner. Carbon fibres have advantages over existing chaff materials as they are fine, light and much stiffer than existing chaff materials. The electrical resistance is about 1000.times.higher than that of aluminum however and this invention therefore proposes the use of carbon fibres coated with a much more conductive coating. Typical coating materials can be copper, silver aluminium applied by a number of different methods.

Abstract: A phase lock loop circuit comprises a variable frequency oscillator having a control input and an output, a divider having an input coupled with the output of the oscillator and an output coupled with the first input of a phase or frequency comparator. The comparator has a second input for a reference frequency (F.sub.REF) and an output coupled with the oscillator control input for providing a signal which is related to the difference in phase or frequency of the signals at the first and second inputs to effect phase locking of the oscillator to the reference signal. A detector provides a switching signal when the control signal falls outside a predetermined range and a switch in the phase lock loop is responsive to the switching signal to open the loop.

Abstract: A method of making a diamond heatsink includes securing a number of spaced diamonds to a sacrificial plate and then metallizing them with, for example, a thin layer of gold, silver, copper or aluminium. The plate and the diamonds are subsequently metal plated with a similar metal to the metallization until the diamonds are completely covered. The sacrificial plate is removed and the exposed surface cleaned and polished. Finally the assembly is diced to produce a number of individual heatsink assemblies.

Abstract: A conductive gasket for use in electro magnetic interference protection of electrical apparatus comprises an elastomeric material in which high aspect ratio conductive fibres are embedded to provide the conductive paths across the gasket. Preferably the fibres are carbon fibres.

Abstract: A phase detecting arrangement includes an edge-triggered flip-flop phase detector which produces alternate logic 1 and logic 0 outputs in response to the arrival at respective detector inputs of set and re-set pulse transitions. These pulse transitions occur in pulse trains derived respectively, from external synchronizing signal generating means and a voltage-controlled oscillator the frequency of which is to be synchronized with that of the synchronizing signal. First and second sampling devices are associated with the phase detector for sampling the output from the detector when set and re-set transitions occur at inputs to the first and second sampling devices.

Abstract: A digital telephone exchange including a first and second processor in which the second processor contains algorithms selectable by the first processor for operation of functions within the exchange, and in which subscribers' apparatus is connectable to both processors via bus structures and in which signals are passed along the bus structures between connected subscribers under the command of both processors.

Abstract: Apparatus for measuring the spot size of light emerging from an optical fibre comprises a rotating radial grating which is moved relative to a monochromatic beam of light, passing through the fibre, to vary the spatial frequency of the light entering a photodetector situated at the output end of the optical fibre, thereby obtaining a variation in the modulation amplitude of the light received by the detector, allowing measurement of the spot size to be obtained.

Abstract: A tool for accurately positioning a flat pack multi-lead component to a PCB during soldering of the leads. The tool has a double function in providing both an accurate location for the board and the component while re-flow soldering takes place. It also provides fool-proof orientation of the component. The basis of the tool is four locating pins which locate at the corners of a square flat pack component but each pin is accurately made and positioned to locate the end leads of the two adjacent sides with a small clearance from the moulded body itself. This takes account of variations in the moulded bodies. One corner of the square body is chamfered and one of the pins is similarly shaped to ensure correct orientation.

Abstract: A diamond heatsink assembly includes a multifaceted diamond mounted on a metal heatsink. The diamond may be partially embedded in the metal heatsink by pressing, soldering or clamping or the metal heatsink may comprise a split collet arrangement so that the diamond is removable. An electronic component such as a multimetric or a micrometric wave device can be mounted on one or several facets, and a faulty component can be removed and a new one secured to the same or another facet.