Patent GB-631624-A (GB)
Title: Improvements in or relating to electrical pulse communication systems
IPC: H04B7/17
Filed: 1947-08-07
Abstract: 631,624. Multiplex pulse signalling. WESTERN ELECTRIC CO., Inc. Aug. 7, 1947, No. 21767. Convention date, June 11, 1946. [Class 40 (v)] In a communication system in which signals are conveyed by one or more channels comprising a train of code groups of pulses, additional signals are conveyed by time modulation of the pulses in the train. In the system described, the additional signals form an order wire channel and are inserted at a radio repeater station, to convey speech or ringing current. In the two-way repeater station, Fig. 2, the tower 210 comprises receiving aerial 244 feeding receiver section 242 feeding I.F. signals to the video section 240 located at station 212. The pulse output from section 240, which may comprise eight interlaced pulse code channels, is fed to repeater assembly 255 at location 213 where the signals are reformed and time-modulated. The output from 255 is passed to the radio transmitter 251 and aerial 253 on tower 211. A similar arrangement is provided for the transmission of signals in the opposite direction, the signals being received by the aerial 254 and retransmitted from aerial 243. The repeating amplifiers 267, 266, are provided with emergency pulse supplies 269, 268, respectively. Order wire equipments, including keys 263, 262, bridging-units 265, 264 and telephone sets 271, 270 are connected by cable 295. Additional telephone sets 272, 273 are provided at the towers 210, 211 to facilitate adjustment of the equipment by service personnel. The functional diagram, Fig. 3, gives further details of the circuits of the system. Signals from the radio receiver are passed to pulse lengthener valves V1, V2, followed by a pulse - generator V3 which produces a sharp pulse at the trailing edge of each lengthened pulse. Generator V3 is followed by pulselengthening valves V4, V5 whose circuits are adjusted to produce 1¢ microsecond pulses. A further pulse generator V6 is actuated by the trailing edges of the input pulses and is followed by pulse-lengthening valves V7, V8 producing pulses of the duration required for retransmission. These are fed to the radio transmitter through amplifiers V9, V 10, V 11. Pulses from V5 are amplified at V12, the amplifier having a low decrement resonant circuit in its output, in which an oscillatory current continues to flow during the times when pulses of the type which maintain it are absent due to coding. The oscillatory output is limited and clipped in valves V13, V14 and passed to a crystal-controlled oscillator circuit V15, V16. The pulses are thus employed to maintain the oscillator frequency substantially in synchronism with the received pulses. In addition the pulses are passed through the crystal element Y1 and the time variations thereof substantially removed. These pulses then serve as a reference which is compared with the time-modulated pulses by means of a modulator valve V17. The output of V17 is demodulated by valve V18A and the output fed through amplifier V19A and filter FL1 to the receiver at the repeater point. Signals from the local microphone pass through amplifiers V23, V24 to modulate the output of pulse generator V5 by varying the duration of its output pulses. The gain of amplifier V23 is controlled by the audio output of filter FL1 which is rectified and amplified in valves V22A,.V22B, V18B, so as to limit the .pulse excursions to the available limits. Ringing current is applied to rectifier V20A, D.C. amplifier V19B and a relay control valve V20B controlling the local source S1 of ringing current. In the absence of received pulses., the order wire channel is operated by pulses from an emergency source controlled by a relay S2 which is normally energized by rectifier V26 fed with received pulses from amplifier V25. For emergency operation, relay S2 disables the first pulse lengthener V2 to reduce random received noise and the emergency pulses are derived from a multivibrator V28 controlled by a pulse generator V27 supplied from the crystal oscillator V15, V16. The Specification describes detailed circuits for carrying out all the functions referred to in Fig. 3.