Abstract: A connector for monomode optical fibres comprises two connectable housings in each of which is secured the end of an optical fibre which is substantially coaxially aligned with at least two light displacement means which produce a light beam with a predetermined form from light transmitted along the optical fibre. The light beams from the two housings are complementary so that a light beam from either housing is focussed onto the end of the optical fibre in the other housing when the two housings are connected. The light displacement means may be convex or concave lenses, SELFOC (Registered Trade Mark) lenses, prisms or combinations of these. The light beam from each housing is preferably parallel but one can be divergent and the other convergent. They may also both be divergent with an additional lens between the housings.

Abstract: A method of fabricating optical sensing devices for detecting displacement of a part thereof comprising the steps of bonding a multiplicity of optical devices to one surface of a relatively large transparent substrate so that the optical devices are accurately located relative to one another and to the substrate itself, securing to the opposite surface of the substrate and one surface of a transparent optical element-carrying substrate in parallel relationship thereto resilient spacer support means and dividing the entire assembly into individual unit parts each of which comprises an optical device bonded to one substrate unit and coupled to another substrate unit having its own optical element by a divided part of the resilient spacer support means so that the two substrate units are resiliently mounted relative to one another whereby relative movement between the two substrate units produces variations in the optical characteristics of the device which can be sensed.

Abstract: A target tracking transmitter has an internal voltage supply which may be operated at a first operative level and a second reduced operative level. A switch is provided for cycling the voltage supply between the first and second operative levels, which are both sufficient to ensure generation by the transmitter of radio frequency signals for detection by a remote receiver. The switch is arranged to control the time for which the transmitter is cycled at the first and second levels whereby the operating life of the internal voltage supply is maximized while enabling continuous generation of the radio frequency signals.

Abstract: To facilitate ring trip detection in a telecommunications exchange the ringing signal applied to a customer line is limited to provide a square wave output. Since when the customers instrument is "on hook" virtually no direct current flows in the line, the square wave output has substantial 50--50 duty cycle and when the customer instrument goes "off hook" the d.c. alters that duty cycle, by sampling the square wave signal and counting up for, say, positive samples and down for, say negative samples, any significant change in the duty cycle causes a counter to exceed a ring-trip threshold fairly rapidly. An algorithm and circuit using the algorithm to facilitate identification of "ring trip" based on the above feature are disclosed herein.

Abstract: Featurephone III Provides a line powered loud speaking telephone which meets BSI standards for current drain.To maintain the instrument at a fixed position on a V/I curve a constant current drain is provided across the line form which the instrument amplifier is fed. Accordingly, regardless of amplifier power requirement variations, current drain from the line is constant.

Abstract: The inter-bus system provides the communication interconnection between communication systems to form a large telegraph packet switching exchange for example. The fast inter-bus system uses an RS-485 interface, however, the specific protocol used has particular speed advantages. The inter-bus system consists of a bus converter for each communication system interconnected by a bus involving 16 data bits, a pair of parity bits, clock, abort, transmit active, address strobe and grant return paths. The bus converters are chained by a grant link arrangement. The grant link is used to carry a grant pulse which is passed on around the chained bus converters to identify the master converter for an inter-bus system transfer. When the grant pulse is received by a bus converter wanting to transmit, that bus converter breaks the chain and performs the transmission required. When the transmission is complete the completing bus converter surrenders its master state by generating the grant pulse.

Abstract: An integrated circuit having a built-in self test design, the integrated circuit including a combinatorial logic circuit, a first register coupled to an output of the combinatorial logic circuit and a feedback path via which output signals from the first register are fed back to an input of the combinatorial logic circuit. A multiplexer is provided between the first register and the feedback path, and there is also provided a second register responsive to a signal which is originated to initiate a test function for feeding test signals via the multiplexer and the feedback path to the input of the combinatorial logic circuit.

Abstract: A fibre optic modulator comprises an optical fibre 2 and a waveguide 10 of active material. The waveguide 10 is dimensioned such that any mode of the waveguide has a propogation constant which is separated from the propogation constant of the optical fibre mode by an amount equal to or greater than .lambda./L where .lambda. is the wavelength of transmitted electromagnetic radiation in the mode of the optical fibre and L is the length of the effective portion of the waveguide of active material.

Abstract: An optical line simulator comprising input and output ports for coupling to optical fiber, a partially transmissive plane mirror interposed in the optical path between the ports, a reflector adjacent to the mirror and a variable density neutral filter in the optical path. This device simulates path delay and loss. These factors can be varied independently by adjusting the distance between the mirror and the reflector, and by varying the filter density.

Abstract: An electrical firing arrangement for the sequential firing of a plurality of mortars stacked in end-to-end relationship within a single launching barrel. The firing arrangement comprises a pulse generator for producing mortar firing pulses and a circuit for applying these pulses to an electro-magnetic stepping switch which applies the pulses in turn over pairs of wires to igniters of the respective mortars as the stepping switch is stepped from one position to the next. The stepping switch comprises normally-open contacts which close when an operating coil is effectively energized by a firing pulse and switch wipers move out of engagement with one pair of associated contacts on the stepping switch towards the next pair of associated contacts on the same switch.

Abstract: A launching barrel/oscillator module simulation unit is provided for simulating a plurality of launcher barrels and associated oscillator module of an aerial (infra-red or chaff) decoy arrangement. The unit is adapted for connection to a launcher control module (LCM) of the arrangement which sends command information over a data link (DB) for the operation of the launcher/barrel oscillator module (LCM) in accordance with specific decoy requirements. The unit is effective for sending status information back to the launcher control module (LCM) over the data link (DB) and basically comprises (i) a plurality of switches in respect of each simulated barrel and operable in dependence upon the condition (e.g.

Abstract: A pyroelectric detector element having defined on a major surface two spaced areas exhibiting radiation absorbing and/or reflecting properties. A mirror-like area comprising a dielectric material is provided in at least part of the space, and preferably extends over all or substantially all of the space, defined between the two spaced areas to reflect the radiation and provide a substantially nil output contribution for the radiation falling on the space.

Abstract: Radially fed microwave signal combiner/distributor apparatus comprising a central coaxial connector which is coupled via radially extending paths to several circumferential coaxial connectors which are equiangularly disposed on the circumference of a circle surrounding the central connector, the apparatus including a generally discoidal microwave transmission cavity through which the paths extend, which cavity communicates at the center thereof with the central coaxial connector and which cavity communicates at the circumferential periphery thereof with the circumferential coaxial connectors via a conductive annulus, which annulus is spaced away from the internal circumferential periphery of the cavity, and to which annulus the inner conductors of the circumferential coaxial connectors are electrically connected at locations equiangularly spaced around the annulus.

Abstract: A method of fabricating two terminal mesa semiconductor devices comprising etching a surface doped and metal coated silicon slice thereby to form a plurality of silicon frusta each capped by a metal contact pad, covering the frusta side of the slice with a metal contact continuity layer and then with a handle layer formed to lie parallel with that surface of the silicon slice which is remote from the frusta, lapping away the silicon slice to expose parts of the handle layer which extend between the frusta so that the frusta are separated so as to define discrete mesas held together by the handle layer, forming one of the two terminals on a face of the mesas remote from the contact pads, removing the handle layer to reveal the contact pads and bonding each contact pad thereby revealed to the metallized face of a diamond heat sink, one heat sink to each contact pad, which heat sink forms a part of the other of the two terminals of each mesa semiconductor device.

Abstract: A method of producing a layered structure, the method including forming a spacer layer on a substrate, forming a parting layer on the spacer layer, forming a first masking pattern on the parting layer the first masking pattern delineating field regions in a first metal layer, etching the spacer layer and the parting layer in accordance with the first masking pattern, depositing a first metal layer, depositing an etch barrier layer, dissolving the parting layer to remove the masking pattern and the first metal layer and etch barrier layer in the field regions, depositing a passivation layer on the spacer layer, depositing a dielectric layer on the passivation layer, forming a second masking pattern on the dielectric layer, exposing the etch barrier layer in accordance with the second masking pattern, depositing a second metal layer, forming a third masking pattern on the second metal layer and etching the second metal layer in accordance with the third masking pattern.

Abstract: In local area networks (LAN's) which are required to operate in duplex mode it is necessary for the common communication medium to be operated in a t.d.m. manner. Because the LAN has no common equipment, every station is arranged to contain its own control circuitry and crystal controlled clocking system to produce time slot markers. The system is organized so that each time slot comprises an active period for data or speech transmission or contention resolution, followed by a transit period in which the data or speech reaches the destination. Ideally time slot markers occur simultaneously in both stations and for intermediate stations there is a tolerance which reaches a maximum at the midway point of the network communication medium. The multiplexing system arranges that the time slots are packed as closely together as the delay between most separated stations will allow.

Abstract: A switch mode power supply comprises an oscillator arranged to drive the primary winding of a transformer. A nuclear impulse detector is arranged to discontinue drive to the primary winding in response to detection of a nuclear impulse.

Abstract: A control circuit comprising a read-only memory has its storage area divided into two areas each containing the same number of addressasble words. By arranging that input of a single address signal causes a change from addressing a particular wood in one area to addressing a corresponding word in the other area, and by programming a fixed difference in value between corresponding words in the two areas causes a step function in the output. Using a digital to analogue converter on the output of the circuit permits a step change in a voltage output to be provided to (e.g.) a voltage controlled oscillator. A control circuit using a read-only memory as a voltage comparator is also disclosed.

Abstract: A microwave antenna comprising a dielectric substrate, carrying on one side thereof a microstrip antenna suitable for operation within a first frequency band and on the other side thereof a conductive ground plane, a first microwave feed coupled between the microstrip antenna and the ground plane for conducting microwave signals in the first band, at least one radiation aperture formed in the ground plane for operation within a second frequency band and arranged to communicate with a resonant microwave cavity defined between the ground plane and a conductive enclosure arranged to extend therefrom, and a second microwave signal feed coupled between the ground plane and the said enclosure for conducting microwave signals in the second band.