Patent GB-311451-A (GB)
Title: High frequency signalling over wires
IPC: H04B3/58
Filed: 1928-02-11
Abstract: 311,451. Standard Telephones & Cables, Ltd., (Western Electric Co., Inc.). Feb. 11, 1928. Wired-wireless systems; repeating systems.- A signalling system in which high-frequency signalling currents are superposed upon a powerdistributing line is characterized by the provision of a repeater station-for repeating or conveying the signal currents past a discontinuity in the power line, such as a voltage-transformer or an open power-switch, without modifying the normal power-transmission path. The repeater may also be employed on a continuous line, or to connect the carrier circuits of two separate power lines at a common point. Provision is also made for enabling conversation to take place between any two stations on either side of a break in the power line, or upon the same side of the repeater should the latter break down. Stations on one side of the repeater transmit the carrier signals on a given frequency, say 100 kilocycles, whilst those on the other side transmit at a different frequency, say 110 kilocycles, whilst both receive at a frequency say of 80 kilocycles, the repeater circuits being so arranged that incoming signals on one frequency are retransmitted on another frequency. As shown in Figs. 1 to 4, two stations A, B are located on the same side of the " break " or discontinuity 11 in the power line 10, whilst stations C, D are on the other side. Figs. 1 and 2 show the transmitting and receiving circuits of station A in detail, whilst Figs. 3 and 4 show the repeater circuits. Repeats.-In operation, the circuits of say station D on the far side of the repeater transmit carrier waves of 110 kilocycles and receive waves of 80 kilocycles. Modulated carrier-waves of 100 kilocycles fed to the power line 10 by station A on the near side of the repeater pass through the left-hand coupling-circuit 112 of the repeater, Figs. 3 and 4, and thence through a high-pass filter 113 to the collecting circuit 151 where they are combined in the detector 154 with the unmodulated carrier which is also transmitted to line. The rectified low-frequency currents from the amplifier 155 are passed back through a filter 173 to the input of the speech-amplifier 119. Here they are impressed upon a carrier wave of 80 kilocycles from an oscillator 120 and in modulated form are transmitted over line 10 to station D. Similarly the modulated return signals on a frequency of 110 kilocycles from station D are transmitted to the repeater where they are converted into a modulated carrier of 80 kilocycles and are then re-transmitted to station A. Terminal circuits.-The outgoing channel of station A includes an amplifier 19, a constantcurrent modulator 21, an oscillator 20 adapted to produce carrier waves of 80 or 100 kilocycles according to whether the condenser 39 is in or out of circuit with the condenser 38, thereby producing calling signals, and an amplifier 22. The incoming channel extends from the power-line 10 through a coupling-circuit 12 to high-pass and low-pass fillers 13, 14, and includes a common collecting circuit 51, an amplifier 52, rectifier 53, a demodulator 54 for combining the carrier wave and the speech-side-bands, on an amplifier 55. Operation.-Raising the receiver 15 energizes relays 76, 78 and 80, thus preventing operation of relays 84, 85 so that the high-pass filter 13 remains connected to the outgoing channel, and the low-pass filter 14 in the incoming channel. The operation of relay 80 prepares a circuit for the transmitting or selector key 16, whilst the relay 62 is short-circuited through relay 78. The operation of relay 78 also closes relay 30 to light the filaments of the valves 19 - - 22 in the outgoing channel. The outgoing 100 kilocycle carrier passes to the repeater station, and through the right-hand coupling-circuit 112 to the collecting circuit 151. The rectified current from the amplifier 153 operates a series of relays which, inter alia, connects the condenser 139 in the plate circuit of the oscillator 120. The operation of relay 179 causes current from a battery 132 to set the selectors 110 and 117 to receive signals from station A whilst relay 130 is closed to energize the filaments of the valves 119 - - 122 in the outgoing channel. Selector 117 may also be utilized to close a contact which cuts the repeater out of the talking circuit whenever one station calls another located on the same side of the repeater. The operation of selector key 16 at station A, Fig. 1, energizes relay 86 intermittently so that interrupted pulses of 100 kilocycle current from the oscillator 20 are transmitted to the power line 10 and thence through coupling-circuit 112 at the repeater and filter circuit 113 to amplifier 153, which in turn operates relays 162. 174, and 177. Interrupted pulses of 80 kilocycle frequency are accordingly fed through low-pass filter 114 and coupling-circuit 112 to both sections of the line. Simultaneously selector 110 and 117 are advanced step by step, whilst relay 190 maintains the closure between the incoming and outgoing repeater channels. The calling impulses of 80 kilocycles operate the selector at the required station only, all other station selectors falling back to starting point. The bell 178, Fig .1. at the required station is rung through the armature of relay 94.