Abstract: Bistable operation of ferroelectric liquid crystal smectic I* or smectic F* cells is disclosed which uses a greater liquid crystal layer thickness than is achievable with smectic C* material while yet retaining bistability of operation. One or more such cells are employed in two-dimensional information processing apparatus.

Abstract: The data processing terminal comprises a smectic liquid crystal flat panel display module (2) which is supported by a support module (1). The terminal also includes a keyboard (4). The display module (2) may be removed from the support module (1) and has its own central processor, memory, control means and power source to enable it to operate independently of the support module, which contains its own central processor, memory, control means, and interface means and is mains operated. The display module may incorporate a touch sensitive overlay to permit the manipulation of the contents of the display. The support unit may incorporate a telephone interface unit.

Abstract: Hydrogen evolution in an optical fibre is suppressed by the incorporation of a hydrogen absorbent material in a water blocking compound with which the cable is filled. Typically the absorbent material is a silver substituted zeolite.

Abstract: An arrangement for the demodulation of auxiliary low frequency channels in digital transmission systems comprising means (12) for receiving the transmitted signals, linear amplification means (13) with automatic gain control (AGC) (14) for the received signals, non linear discrimination means (15) for discriminating between logic levels in the amplified digital signals at the main channel bit rate, and subtraction means (16) for subtracting the output of the discrimination means from the amplified signals to obtain the auxiliary low frequency channel signals.

Abstract: A design of optical fiber cable that is gas blocking has a set of four plastics packaged optical fibers (2) around a central strength member (1). The fibers and strength members are embedded in spaced apart relationship in a nylon 12 pressure extruded sheath (3) which has been annealed to provide a contraction in the region of 1/4%.

Abstract: A simple radio receiver for FSK signals is described in which the signals from the aerial are mixed in two high-gain mixers respectively with local oscillator signals in phase quadrature and at the signals' nominal center frequency. The outputs from the mixers are low-pass filtered to get the difference frequencies. The filter outputs are amplified and one applied to the D input of a D-type flip-flop to the clock input of which the other is applied. The flip-flop output gives the FSK modulation. It is highly desirable that the local oscillator's outputs, called Io and Qo should be in accurate phase quadrature, and the circuit described herein is intended to achieve this. To do this, the Io and Qo signals are applied to a quadrature phase sensitive detector (10) which, if the phase relation is wrong, gives an error signal. This is applied to an adjustable phase shifter (12) in one of the oscillator outputs, in this case the Qo output. Alternatively, the phase adjustment can be applied to both Io and Qo lines.

Abstract: A steered adaptive antenna arrangement including an adaptive beamforming network 10 to which the output signals of an array of antenna elements are applied, the network having a feedback wherein the summed output of the network is correlated with each element signal, applied to a limiter and added to the steering component whereby the derived value is used to drive the associated weight coefficient, characterized in that the summed output of the beamformer network 10 is further applied to a desired signal estimator 11 the output of which is subtracted from the summed output to provide the feedback input 12 to be correlated with each element signal.

Abstract: A system of the local area network (LAN) type using a closed loop optical fibre transmission medium, in which a series of stations, one of which acts as a master station, are connected to the loop. In each TDM cycle, a group of adjacent time slots is used as a framing group which occurs once per cycle of the system, the framing group including a multi-bit group number position which identifies a slot or group of slots. The loop includes a latency buffer to set the loop delay time to exactly 125 micro seconds, and the system according to the invention provides for both circuit-switched and packet-switched connections. To set up a circuit-switched connection, a free slot is chosen and its identity signaled in a packet manner. The proportion of slots allocated to circuit connections is varied dynamically, with indication thereof conveyed in a framing group of slots which occurs once in a cycle.

Abstract: In a fiber optic interferometric magnetic sensor or magnetic gradient detector a magnetic bias field is applied to a magnetically sensitized portion of an optical fiber by means which are driven by optical power whereby a completely passive sensor head arrangement may be achieved. In a magnetic gradient detector optical power from a high power laser (34) may be supplied via an optical fiber (35) to illuminate a solar cell 27 to whose electrical output terminals solenoids (25,26) are connected. A portion of a respective optical fiber (21, 22) which is magnetically sensitized, by for example bonding to a strip of magnetostrictive material (23, 24), is disposed inside each solenoid (25, 26).

Abstract: A packet switching system has both speech and data transmitted as packets over virtual connections set-up in a digital network. The speech and data packets are transmitted at the bit rate of the transmission medium. The speech packets, which have to be handled in real-time, are given priority over the data packets, which are relatively long. Because the speech packets may be subjected to unacceptable delay if the medium is busy with a data packet when a speech packet is to be sent, the system provides that, if a speech packet arrives when a data packet is partly sent, the sending of the data packet is interrupted, the speech packet is sent, and the residue of the data packet is sent when the transmission medium is free of speech. This residue is provided with a new header and handled as if it is a new data packet.

Abstract: In a data transmission system of the TDM type both circuit-switched and packet-switched connections can be set up. Circuit-switched connections, being real time, e.g. voice, are given priority, but all time slots are available for packets when not in use for circuit-switched connections. Thus the ratio of the two types of connections is automatically adjusted according to traffic conditions.

Abstract: A method of addressing a matrix addressed ferroelectric liquid crystal cell is described that uses parallel entry of balanced bipolar data pulses on one set of electrodes to co-operate with serial entry of unipolar strobe pulses on the other set of electrodes. Data entry is preceded with blanking (erasing) pulses applied to the strobe lines. The polarity of the strobing and blanking pulses is periodically reversed to maintain charge balance in the long term.

Abstract: A telecommunication system is structured on a multi-plane basis, having an information transfer plane (3), and one or more other planes (4, 5). When a call is set up an initial connection is made via the first plane (3) in packet switched manner. If other services such as voice are needed, connections between the user's terminals are set up on a circuit-switched basis, under control of the connections already set up in the information transfer plane. These additional connections are only maintained as long as needed.Note that whereas connections are set up in packet manner in the information transfer plane, they are set up in circuit switched manner in the or each other plane.

Abstract: In operating a display device incorporating a matrix addressed smectic cell, a strobing pulse is applied to each row electrode in turn while data pulses are applied in parallel to the column electrodes. The data pulse voltage excursion is less than the minimum voltage V.sub.T required to switch the cell. For the entry of complete rows the strobing voltage excursion is made larger than twice V.sub.T for fast data entry. For entry of rows in successive segments (e.g. for single character entry) the strobing voltage is less than twice V.sub.T so that successive strobing pulses applied to a single line may be of longer duration but cannot give rise to spurious switching of unselected pixels.

Abstract: An optical fibre connector which can be connected or disconnected underwater without contamination of optical fibre termination lenses. When the connector is disconnected, the terminations of each connector element are disposed in respective chambers which are sealed by respective diaphragms. Upon connection the two diaphragms are brought into sealing contact and the terminations of one connector element caused to enter the chamber of the other connector element following penetration of both diaphragms.

Abstract: A magnetic field sensor is comprised by a length of magnetically sensitized single mode optical fibre wound in substantially random directions on a sphere of non-magnetic material, so that an omnidirectional response is obtained. Specific directionality can be obtained by application of a dc bias field in the desired direction. All three perpendicular components can be measured by applying three perpendicular ac fields at different frequencies. The sensor is intended for use in all fibre Mach-Zehnder interferometer types of magnetometer or magnetic gradient detector, examples of which are described.

Abstract: In an optical transmission system, particularly a submerged system, a line finding system is provided which, in the event of a fault somewhere along the system, enables the remaining operative lines or paths to take over the traffic and thus "steer around" the fault. The laser sources of the submerged repeaters and switched by electrical selection at their input using failed clock or a supervisory signal to achieve the switching.

Abstract: In a cordless telephone it is usual for the base station and the handset to be allotted a single address code to provide "dial security". Such an address code is usually programmed in during manufacture. In the present arrangement, a printed circuit board (2) in the handset or base station bears a single common track (5) and a set of tracks (6) adjacent to it. Each cordless set's two units also has a label (1) with a set of conductive strips on it which is secured to the board so as to connect the common track and a selection of the individual tracks. Thus energization of the common track (5) energizes a selection of the tracks (6) according to the address.When a number is to be sent the address code defined by the handset's label is sent to the base station and compared with that for the base station's label. If they agree, "dialling" is permitted.The label can also be wrapped round the edge of the board or plugged into a socket on the board.

Abstract: A therapeutic material is contained in a water soluble glass having a dissolution rate that is distinctly pH sensitive, the ratio of dissolution rates between pH 2 and pH 6 being greater than 60 to 1. The glass incorporates phosphorus pentoxide as the glass former and an alkali metal oxide and one or more alkaline earth metal oxides as glass modifiers.

Abstract: Oil concentration levels in water are measured by a light scattering/absorption technique. The intensity of directly transmitted and scattered light signals are compared to provide a correction factor corresponding to the level of solid contaminents in the mixture. This correction factor is then applied to a signal corresponding to the intensity of light transmitted directly through the mixture to provide an accurate oil concentration measurement.