Abstract: An oscillator is provided with an internal, high gain hysteresis effect so as to offset the linear regions of the waveform and to avoid spikes upsetting the count of a reference divider controlling the oscillator. The crystal (10) and capacitor (11) are connected between the base of one (T.sub.1) and the collector of the other (T.sub.2) transistor of a long-tailed pair, signals appearing at the collector thereof being fed via emitter followers (T.sub.5, T.sub.6) to a further long-tailed pair (T.sub.7, T.sub.8) having tapped collector resistors (R.sub.1, R.sub.2). The signal appearing at the tapping point of one of the further pair (T.sub.7) is fed to the base of a transistor (T.sub.3) whose collector-emitter resistor lies in the load circuit of one of the transistors (T.sub.1) of the first long-tailed pair.

Abstract: A dry solder reflow process, in which metal surface oxides are removed from the solder surface by abstraction of the oxygen from the metal oxide by atomic hydrogen, the atomic hydrogen being created within an intense microwave frequency plasma of a gas containing hydrogen.

Abstract: In order to reduce noise in single or multiloop analog to digital converter circuits employing n-bit quantisers (n>1), only the MSB of the quantiser output is fed back in a feedback loop in reduce problems of overload in a feed-forward (integrator filter). The feedback MSB may be subtracted as an offset from the input analog signal or used to control the sign of inversion of a signal inverter.

Abstract: A process for the manufacture of a transistor device of the type having active regions e.g. an emitter (17) and a base (11) each contacted by isolated extended conductive regions (37, 33) respectively. At start of process a mesa structure is defined in layered III-V material (3, 5, 11 and 13). The sidewall of the mesa is covered by a conformal coating (27) of insulating material; and, lattice matched material (33) grown on the exposed adjacent material (25) to form a first extended contact. This then is covered by a further layer (35) of insulating material (35). The second extended contact (37) is then grown over the mesa active region material (13). This contact material (37) is isolated from the first contact material (33) by the remanent insulating material (27, 35). This process is applicable to the GaAs/GaAlAs III-V material system as also other material systems. Transistor devices produced by this process may be either bipolar or field-effect type.

Abstract: A converter for digital radio applications, consisting of a parallel analogue to digital converter that provides a sampling at signal carrier frequency, or preferably at a harmonic of this frequency. Successive samples are stored in a memory and this is accessed at a lower rate to average numbers of samples. The ADC achieves greater resolution by virtue of this sampling. Filtering is provided by averaging action, but further filtering functions can be performed by an add-on filter. The converter receives modulated analogue signal from an input stage, for example the rf. or if. circuit of a radio receiver. In a modified version of the apparatus, several converters may be utilized in parallel to afford increased data colletion.

Abstract: An HF communications system comprising a plurality of radio stations, each radio station including a transceiver and a control means therefor, the control means including a processor and a memory, the memory storing a model of the ionosphere of a designated region in digital form, wherein the order to establish reliable communications channels between the stations, the system undergoes the following procedure: a first station computes from its stored model a propagation frequency window and determines a set of communications channels within the frequency window, the transceiver of the station thereafter monitoring the noise and interference present in the set of channels in order to reject channels having noise and interference levels higher than a predetermined level, and the first station establishing communications with one or more second stations on communication channels of the set in order to actively sound the channels in order to establish which channels are suitable for message transmission.

Abstract: A guided-wave optical wavelength duplexer fabricated as an integrated optical device, comprising input ports (2, 4) for light at different wavelengths (a.sub.1, a.sub.2) coupled to first and second waveguides (6, 8) formed on a substrate surface, the first and second waveguides having first and second coupler regions (10, 12) to enable light to be transferred from one waveguide to the other, the first and second waveguides as at (26) between the first and second coupler regions being formed as circular arcs having the same center to provide an accurately defined optical path length difference, so that light at a first wavelength (a.sub.1) is output through one output port (14) and the second component (a.sub.2) is output through another output port (16).

Abstract: A semiconductor diode laser array device 1 capable of emitting a high optical power in a narrow beam, the device 1 comprising a surface emission multiridge waveguide structure in which emission can take place from a surface 4 occupying both a longitudinal and a lateral dimension of the device, the dimension in each case being much greater than the emitted light wavelength. Stability in one of said dimensions may be maintained by an array design having a spaced arrangement of laser elements positioned such that the optical field in one element partly overlaps that of a neighboring element. Preferably, the sum of the propagation constant and the coupling parameters to the neighboring elements equals the same value for all the elements in the array.

Abstract: A radar system for determining first time around targets from multiple time around targets using two radar pulse trains of different pulse repetition intervals and thresholding means. Echos from pulses at each pulse repetition interval being compared to determine first time around targets from subsequent time around targets. The radar system uses thresholding levels to determine an echo and is less prone to problems of coincidence gate clashing with high duty cycles.

Abstract: A structure for reflecting visible light or near visible light, wherein the structure is formed of a low dielectric constant material having an external surface comprising an electrically conductive layer of material which has an array of slots therein so as to be substantially transparent to microwave radiation of a predetermined wavelength which will impinge upon the structure during use, while being reflective to light.

Abstract: A transceiver interference cancellation system having an adaptive processor for receiving signals from a number of antennas and for suppressing particular signals from the antennas. The system includes a code generator which controls a switch to provide transmitted signals with a predetermined pulse code. Means including a code correlator are provided for detecting the pulse code in received signals and for controlling the operation of the adaptive processor such that wanted signals when identified are not suppressed.

Abstract: A security arrangement for grooved shafts or bolts uses a plurality of toothed collet members held in securing abutment by a cap member. The cap member is held in position by a displaceable chock member. The chock member is readily displaceable such that the securing arrangement can be rapidly released. Conveniently, the chock member may be displaced by a spring member, the spring member being held in a bias position by a cord attached to the chock member.

Abstract: An optical sensing system comprising single light source and a series of phase shifting switching devices positioned linearly aligned with the light source. Each phase shifting device is driven by a driving device with pulses at different frequencies and sequentially from the most proximately located phase switching device to the most distant phase switching device so that light eventually passes through each of the phase switching devices. Fiber sensor arrays are aligned with each of the phase switching devices and light reflected from the fiber sensor arrays is detected by a plurality of photodetector devices each associated with a fiber sensor array.

Abstract: In order to overcome problems in an active noise reduction system of sound buffets at low frequency and signal enhancement caused by imperfect transfer functions of a noise cancelling sound generator and a microphone, one or more high pass filters for reducing low frequency signals are provided in a feedback loop between the sound generator and microphone. A low pass filter is provided for extending the bandwidth of the system but which does not introduce unduly large phase shifts.

Abstract: An FM demodulator comprises an injection locked oscillator/divider for receiving an input signal to be demodulated. The injection locked oscillator/divider is coupled via a divider to a frequency discriminator, such as a quadrature demodulator, for providing a demodulated output signal. A feedback loop is provided to afford the demodulated output signal to a varactor tuning circuit of the injection locked oscillator/divider so that the center frequency of the injection locked oscillator/divider is constrained to correspond with the frequency of the input signal. The FM demodulator provides improved threshold extension and demodulated video bandwidth.

Abstract: Many optical sensing systems include an interferometer comprising a plurality of contiguous optical fibre sensor lengths with partially reflecting discontinuities therebetween. An inherent problem with these systems is however that the number of sensors that can be configured is limited by the pulse repetition or sensor interrogation rate. In the present system the pulse repetition rate is effectively increased without having to reduce optical fibre sensor lengths or numbers by interleaving several interrogating signals.

Abstract: A low frequency digital notch filter comprising two sub-filters - an all-pass-network filter (1) and a T-section filter (3) with a feedback connection from the T-filter to an input node (31), and feed forward connection from this input node to a terminal output node (33). The all-pass-network filter (1) has a transform function:A(Z)=[Z.sup.-1 +K]/[1+K.sub.1 Z.sup.-1]; andthe T-section filter (3) has throughput and tap transform functions:B(Z)=[(K.sub.3 +K.sub.2 .multidot.K.sub.4)Z.sup.-1 -1 ]/[1-K.sub.3 Z.sup.-1 ],and,C(Z)=K.sub.2 Z.sup.-1 /[1-K.sub.3 Z.sup.-1 ],where Z.sup.-1 is the unit delay operator and K.sub.1 to K.sub.4 are multiplier coefficients. The T-section filter 3 may be implemented using a combination of three multipliers (19, 21 and 23) and a delay element (25).

Abstract: A control circuit, particularly for use in a phase-locked loop includes a read-only memory (ROM) having n address inputs divided into two groups, each group being addressed by first (A) and second (B) signals, and the memory device having words preprogrammed therein to provide an output having values (C) of a predetermined function of the first and second signals. In one embodiment the control circuit is employed in a phase-locked loop where one address group provides an analog version of the first signal to a voltage controlled oscillator, and application of the second signal to the second address group permits a step change in the output voltage to the VCO. In another embodiment, the first and second signals may comprise carrier signals and modulating signals in a phase-locked loop employed for frequency modulation.

Abstract: A receiver circuit for data in NRZ1 coding transmitted at high data rates along optical fiber links, wherein in order to overcome problems of phase jitter in the incoming signal, a clock circuit is included comprising a phase locked loop with voltage controlled oscillator for generating a clock signal locked in phase to the incoming data signal, a phase detector for comparing the clock signal with the incoming data signal, a phase frequency detector for comparing the clock signal with a reference clock signal, a multiplexer for switching the phase locked loop to respond either to the output of the phase detector or the phase freqency detector, and a digital counting system for comparing the number of clock pulses generated in a reference period determined by the reference clock, the digital counting system controlling the multiplexer to switch to the output of the phase detector when it is determined that the clock signal is accurately following the reference clock signal.

Abstract: A dividing mechanism for use in frequency synthesizers: comprising:a two modulus divider system having a first and second counter for providing respective programmable count totals A, M, and first counter being coupled to a dual modulus device providing moduli of n and n+1 whereby the two modulus divider system provides a division ratio of (Mn+A) for incoming signals:first and second input means for receiving first and second programming number signals N, Q, synchronization means for receiving a strobe signal from a further counter which provides a count total P, and logic interface means responsive to said first and second input means and said synchronization means to provide programming number signals A, M to said two modulus divider system, the logic interface means being such that in the absence of said strobe signal the two modulus divider system provides a count total C.sub.