Abstract: An optical device comprising a length of optical fibre of predetermined convex configuration supported by fibre mounting and/or attachment means, the convex outer part of the optical fibre having a portion thereof removed therefrom closely adjacent to or even just entering the core of the optical fibre to produce a substantially flat surface therealong on which a reflective diffraction grating of predetermined form is provided according to the function requirements of the device.

Abstract: An electrical detector arrangement is provided having a chopper device for alternately exposing to and obscuring from a detector array a thermal radiation pattern to be detected and imaged. The outputs from the detectors of the array are multiplexed by a multiplexer and then digitized by means of a low cost analogue-to-digital converter. The digital output from the coverter during obscuration of the detector array from the thermal radiation pattern is stored in memory means and this stored data is converted to an analogue signal by a digital-to-analogue converter subtracted from the output of the multiplexer during exposure to and obscuration from the thermal pattern of the detector array by means of a differential amplifier. The output from the differential amplifier which substantially reduces the offset level of the multiplexed detector outputs is then fed to a further low cost analogue-to-digital converter.

Abstract: The Telecommunications system includes at least two exchanges and a plurality of user equipments. Each equipment includes a store for holding a user variable data word particular to that user. Each exchange is provided with a store for holding all the user variable data words of the users connected to it, and each exchange is also provided with its own random variable data word. When a first user makes a secure call to a second user, the first user equipment encrypts the call using its particular variable data word and sends the encrypted data to its own exchange. The exchange decrypts the call using the particular user variable data word that will be used for the call. The exchange encrypts the random variable data word with the particular user variable data word and returns it to the first user. The exchange also sends the random variable data word to the second user's exchange which encrypts it with the user variable data word particular to the second user, and sends it to the second user.

Abstract: In a tuner circuit, the relatively high voltage used to control a varactor diode of the circuit is derived using a cascade of resistors and transistors under the control of a reference voltage input. The breakdown voltage of each transistor is significantly less than the output voltage of the cascade and is such that the cascade can be implimented in the same semiconductor chip as high frequency, low voltage process, synthesiser components.

Abstract: A linear A to D converter comprising a combiner means to which an input signal to be converted is fed, the input signal being combined subtractively or additively with an analogue feedback signal, and the combiner means being arranged to feed an A to D flash converter via an amplifier, which A to D flash converter is arranged to feed a D to A converter which provides the feedback signal. The D to A converter comprises a digital overflowing accumulator also arranged to drive a finite impulse response filter having a plurality of serially coupled one bit delay elements, output signals from which are summed to provide the digital output signal.

Abstract: A rotary pressure/purge valve for supplying pulsation free oxygen without the use of an interim oxygen storage tank in the nature of a surge tank or accumulator. This valve is comprised of an air chamber section and a center section, with the air chamber section having an inlet port for compressed air, and the center section having a plurality of passages therein, disposed at equal intervals from each other and with respect to a centerline common to both sections. First valves are operatively associated with first passage ends, and serve to control the entry of charging air into two adjacent passages at the same time. Second valves are operatively associated with second ends of the passages and serve to control the exit of purging air from the passages.

Abstract: A coupler (FIG. 4) comprising a pair of interwined monomode fibers optically coupled along a portion of their length. The diameter of one fiber is significantly smaller than that of the other and this fiber is thus wound helically. A helical pitch not exceeding 10 mm is chosen. For such pitch, the smaller diameter fiber is appreciably longer. The following inequality thus holds:.lambda..sub.c .multidot.L/.DELTA.L.ltoreq.L.sub.c :where.lambda..sub.c is the design wavelength,.DELTA.L/L is the difference in fiber lengths per unit length, and L.sub.c is the interaction length of the coupler. The signal coupling of the coupler is than a strongly peaked function of wavelength. The coupler is suited to wavelength multiplex/demultiplex applications.

Abstract: An optical fibre splice assembly having a pair of spigots and a sleeve, the sleeve having an internal bore of dimension large enough to permit retraction of the sleeve over at least one of the spigots, each spigot having a bore to accomodate an optical fibre adapted to be secured to an optical fibre cable through its coverings. A method for producing such an assembly is also disclosed comprising the steps of:attaching optical cables to spigots;passing optical fibres through a bore in each spigot;retracting a sleeve over one spigot;splicing together the optical fibres;returning the sleeve over the spigots;tensioning the spliced optical fibers; and then, fixing the sleeve to both spigots.

Abstract: A converter of the flash type includes means for amplifying and d.c. level shifting portions of the input analog waveform fed to each A to D converter unit to provide each converter unit with a full voltage input swing relative to the reference voltage for conversion, thereby producing a more accurate digital output.

Abstract: To facilitate installation of cables through bulkheads and other surfaces and to provide electrical protection to apparatus connected to such cables, an assembly comprising electrically conductive blocks (6) clamped in a frame (2) is provided. The mounting blocks 6, each formed of two parts for fitting round a continuous cable length include ribs (11) adapted to grip the sleeving of the cable and an extended rib (10) for contacting screening of the cable. In use, the frame (2) is welded to a bulkhead or other conductive (earthed) element. A section of insulation is removed from the cable and on clamping of the assembly the blocks (6) are compressed together forcing ribs 10 to contact respective screens. Thus any induced electro-magnetic pulses on the cable screens are provided with a low-resistance leakage path.

Abstract: The invention includes a fuel tank containing an emergency supply of fuel for an internal combustion engine in the general proximity of the engine, with the arrangement being such that proper communication from this alternate source of fuel directly to the air-fuel mixer of the engine is effected. The preferred example of the air-fuel mixer is a carburetor. In this way, by utilizing a reliable arrangement for the delivery of fuel directly to the carburetor, a temporary problem with the primary fuel supply can be circumvented.

Abstract: An integrated circuit having a built-in self test facility, the integrated circuit being partitioned into a number of sub-circuits each of which comprises a combinatorial logic circuit and a register. The sub-circuits are coupled together so that each combinatorial logic circuit has its inputs coupled to at least one register, has its outputs coupled to at least one register, and the output of the overall integrated circuit is taken from one or more registers. Each register has its fucntional mode controlled by predetermined signals to an associated local decoder, the functional modes of the registers being selected to initiate a test operation for the testing of the integrated circuit.

Abstract: A circuit (FIG. 4) in which a sub-circuit comprised of a bias transistor (T1), a feedback reisistor (R2) connected between the collector of this transistor (T1) and its base, and, a drive transistor (T2), is connected to its polarity-inverse sub-circuit (T1', R2', T2') in a ring configuration and is initiated by means of current injection from a start-up bias circuit. The latter may comprise a bias transistor (T1"), a drive transistor (T2") the base of which is connected to the collector of the bias transistor (T1"), and a pair of feedback current/voltage divider resistors (R1", R2") in the collector path of the bias transistor (T1"). Following start-up, constant current is maintained by feedback in the ring, and this current may be tapped at an appropriate point in the ring.

Abstract: A device which includes an arithmetic logic unit and a data shifter--e.f. a barrel shifter. The outputs of these are cross-coupled to their inputs by separate feedback connections. A third feedback connection is provided between the output of the arithmetic logic unit and another of its inputs. For added versatility in operation, registers at the output of the arithmetic logic unit and the barrel shifter may include each a selectable by-pass and/or additional registers may be included in parallel therewith. The device is reconfigured by the control of input multiplexers interposed between the feedback connections and the arithmetic logic unit and the barrel shifter.

Abstract: In a time division multiplexed digital switching system intercommunication between telephony groups is by way of a serially operated data bus (2). Allocation of bandwidth on the data bus (2) is on a needs basis under control of a common control responsive (3) to requests from either applications processors or interface modules (10,20). The interface modules (10,20) receive addressing information from the common control (5) on a serially operated control bus (1) only when a change of status of a communication at least partly affecting that module (10,20) occurs. Such changes of status include new communication set-ups, communication clear-down, bandwidth increase and bandwidth decrease. Dynamic re-allocation of bandwidth of the data bus (2) occurs without affecting communications in progress.

Abstract: A sign in accordance with this invention comprises a pair of end members, with each end member having a longitudinal groove, and with each of the end members having a foot portion configured such that the respective longitudinal groove bears approximately a 15.degree. relationship to the vertical. The longitudinal groove in one of the end members faces the longitudinal groove in the end member such that respective ends of a generally rectangular sign of appropriate thickness may be closely received in these grooves. Importantly, the groove in each of the end members is of dual width, with one portion of each such groove being wide and of comparatively shallow depth, whereas another portion of each of the grooves is comparatively narrow, and of greater depth. Because of this arrangement, elongate panel members of either of two different thicknesses can be readily received in a tight fitting manner in appropriate portions of the grooves.

Abstract: A fractional N synthesizer comprising a voltage controlled oscillator for producing an output signal which is afforded to a phase detector via a variable divider to provide a control signal for the voltage controlled oscillator in the presence of a phase difference between a reference signal from a reference source and the signal afforded thereto from the variable divider wherein the synthesizer is provided with first and second accumulators, the arrangement of the accumulators being such that an output signal from the arrangement is provided in which the interpolation sidebands of the first accumulator caused by quantization errors in the first accumulator are cancelled, means being provided for setting the division ratio of the variable divider in dependence upon the output signal.

Abstract: A digital adaptive echo canceller for use in cancelling echo signals caused by trans-hybrid losses in two-wire to four-wire converters comprises first and second adaptive filters (20,22) each arranged to generate synthetic echo signals. Transfer control logic (23) compares difference signals relative to the difference between the synthetic echo signal generated by the first filter (22), and a real echo signal and the synthetic echo signal generated by the second filter (20) and the real echo signal, and if the synthetic echo signal from the first filter (22) is closer to the real echo signal causes transfer of the coefficients of the first filter (22) to the second filter (20) such that the synthetic signal mixed with transmitted speech signals in a mixer (24) is updated when necessary.