Patent GB-395045-A (GB)
Title: Improvements in or relating to carrier current signalling systems
IPC: H04M7/16
Filed: 1932-01-30
Abstract: 395,045. Wired wireless systems. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and WESTELL,. E. P. L., c/o General Electric Co., Stoke, Coventry. Jan. 30, 1932, No. 2202. [Class 40 (v).] In a carrier current system of communication, supervision or control, a pair of carrier channels is coupled by means capable of repeating selective impulses and comprising low-frequency or direct-current apparatus only, all carrier currents being passed through a rectifier or demodulator prior to affecting the coupler. The apparatus shown is adapted for connection at the left hand side to an extension set of terminals associated with a carrier set and selector mechanism of the type described in Specification 395,053 wherein the selector at a station is used both to direct incoming signals to the correct apparatus or to find an apparatus requiring to transmit a signal. Supervisory signalling from station having access to terminals 1 .. 10. When the transmitting station sends impulses a selecting switch (not shown) is stepped to connect the carrier set to terminals 1 .. 10. Relay 1R, 1A are then operated, relay 1R preparing " engaged " tone relay ET and 1A operating stepping magnet SS of the sequence switch. Upon the first step, 1B is operated to close a self-driving circuit for the switch over bank SS2, and initiate a call on the right hand carrier system at contact 1b4 and cause current of answering frequency to be transmitted to the calling station. If the right-hand channel is seized relay 2A is operated. Further impulses are then transmitted from the control station characteristic of the extension on the right hand carrier channel and are received as positive impulses at terminal 10 to step up the register switch RR. Relay C is energized during the train and released at the end' to operate the sequence switch SS two further steps. Further impulses are then transmitted indicative of the apparatus at the selected extension and are stored in the register RT, the sequence switch being advanced two further steps to operate relay X which operates a self-interrupting relay chain X, Y, Z the contacts Z<2>, Z<3> respectively impulsing 1D and driving the sending register SR. The sender SR is stepped up to a contact marked by the register RR, when switch SS is again stepped to terminate the operation of the chain X Y, Z. During stepping relay 1D transmits impulses to the right hand carrier set over terminal 5<1>. After a pause determined by the release times of relays C, CA, switch SS is again stepped and the circuit of X, Y, Z; is again closed and further impulses are repeated corresponding to the setting of register RT. Switch SS is then stepped again to operate relay T which establishes a straight through impulse repeating circuit from 10 to 51 and connects 2D to 10<1> for the purpose of repeating impulses from the selected apparatus back to the control station. The two-carrier systems are thus interconnected and further impulsing between the two systems is effected via relays 1D, 2D. Priority of important signals. If a signal is of major importance, the first train of impulses is such that switch SS completes a circuit via banks SS4, RR2 to terminal 11<1>, but if of minor importance only, the wiper of bank SS4 is stepped beyond the circuit closing contacts. Relay E is operated by engagement of the coupler from either side so that the circuit to terminal 11<1> is closed only if the right-hand system is engaged. The effect of closure of this circuit is to break down the connection engaging the right-hand system and facilitate the transmission of the major signal. Release. Release of the coupler is effected from the calling station. Cessation of the calling carrier current releases 'relays 1A, 1B, which at contact 1b4 releases the right-hand carrier set and at 1b2 completes the homing circuit of switch SS. Switches RR, RT, ST then restore to normal in sequence. Telephone calls. The selective operations are similar to those previously described. A caller on the left-hand system transmits a single impulse to seize the coupler and initiate the engagement of the right-hand system. The wanted number is then dialled to call the extension which transmits carrier of answering frequency modulated with the tone of the calling bell. This is demodulated in the right-hand carrier set and the resulting tone is transmitted over transformer M<2> to modulate the left-hand carrier answering frequency. When the called party answers, speech follows the same path, whilst the speech of the caller follows an exactly similar path through the coupler via transformer M1. Priority of engaging the coupler. In order to prevent two simultaneous callers (one on each side of the coupler) from being connected together the relay 1B is given priority over relay 2B in the bank SS1 of the sequence switch. Upon simultaneous calls, relays 1R, 2R are operated and sequence switch steps to operate 1B. Relays 1R, 2R operate vibrator ET which signals the caller on the right-hand system to replace his receiver. Specifications 359,576, [Group XXXIX], and 395,289 also are referred to.