Abstract: An amplifier arrangement suitable for use in a receiver for use in a telecommunications system is described. The arrangement includes an amplifier and an FET switch arrangement arranged to alter the time constant of the amplifier in dependence upon the incident signal frequency. A balance switch arrangement is arranged such that switching transients of the switch arrangement are cancelled out in the amplifier arrangement.

Abstract: An aligner is used in a digital telecommunications switching system for correcting the drift between the exchange clocking system and the incoming digital line terminated on the digital line termination units DLT. Typically aligners consists of so-called "elastic-lengthed" buffers having two frames worth of storage arranged such that the line information is written into one "frame area" while the time switch is fed from the other "frame area" and vice versa for each successive frame. Such an arrangement has severe limitations from a fault finding point of view. The aligner of the invention consists of a "single chip" containing a set of five half frame serial shift registers together with read and write address counters and associated logic to ensure that separate "read' and "write" shift registers are maintained.

Abstract: A digital switching arrangement for use in a telecommunications exchange handling channels of digital information in time division multiplex form. The digital switching arrangement being particularly suited for use in stored program processor controller environments. The arrangement comprises a digital switching network and a control equipment. The control equipment includes an input queue and an output queue each arranged to store processor input and output messages respectively. The control arrangement is arranged to asynchronously process each output message to process switching network path connections and to generate in the input queue an input message indicative of the actions performed. Each output message includes switching network identification information indicative only of the identities of the incoming and outgoing exchange highways and channels to be involved in the switching network path to be processed.

Abstract: A conventional interface for 2-wire telephone lines to a digital switch includes line current feed resistors and a bridge circuit where the line impedance is compared with a compromise balance network. The accuracy of the balance determines the proportion of the signal received on the receive pair being retransmitted in the transmit direction. The ratio of these signals is known as the Trans-Hybrid loss and should be as high as possible for good quality speech.In practice the telephone line impedance increases with length as also does the DC resistance of the line and thus the line current, assuming a constant voltage source.It is proposed that the line current feed resistors be formed on a common substrate using well-established film deposition techniques and the balance resistor be formed on the same substrate using a material having a negative temperature coefficient.

Abstract: The basic dual channel pcm coder/decoder arrangement provides PCM/Analogue Codec facilities for use in speech transmission and comprises (a) a pair of transmit channel amplifiers and a pair of receive channel amplifiers controllable for mutually exclusive operation by channel switches and (b) a comparator together with segment-defining ladder networks and associated current steering switching (and compensated current sources). In the encode (A-D), the unit functions as a successive approximation encoder; the particular transmit amplifier creates a voltage condition across the resistors of the two ladder networks and this condition is balanced by the voltage generated by the current sources. A null is consequently produced at the comparator input to govern the PCM output. In the decode mode, both transmit amplifiers are switched "off" and the requisite receive amplifier is switched "on".

Abstract: A digital switching telecommunications exchange handling pulse code modulated information samples in time division multiplex form on incoming and outgoing junctions. The exchange includes a receive interface for each incoming junction and a transmit interface for each outgoing junction and a pair of identical time division multiplex switching networks providing interconnection paths between any incoming junction channel and any outgoing junction channel. Under non-fault conditions exchange calls use indentical paths in each network and the transmit interfaces include error checking and comparison arrangements for each pair of information samples received under fault conditions the transmit interfaces can be arranged to select the non-faulty sample on a per channel basis or can be biased to select one network exclusively.

Abstract: A heat exchanger for central heating in which water to be heated passes through a circular array of parallel tubes. Hot gas passes over the outside of the tubes and heats the water up. Metal wire interlaces the tubes and helps conduction heat from the gas to the water. Preferably the arrangement of tubes and wires is metal coated to further help the heat conduction.

Abstract: An inlet line connected to the inlet of a hydraulic pump includes a jet pump having a Venturi nozzle though which the aspired liquid is passed, and into which a coaxial jet of liquid under higher pressure is introduced to raise, by jet-pump action, the pressure of the liquid at the pump inlet.

Abstract: Constructions for radio antennae, whose size is made appreciably less than the size of conventional antennae by using the dielectric properties of a mixture of barium titanate and strontium titanate.