Patent GB-222104-A (GB)
Title: Improvements in carrier wave working over high tension lines
IPC: H04B3/54
Filed: 1924-09-03
Abstract: 222,104. Western Electric Co., Ltd., (Assignees of Wolfe, W. V.). Sept. 22, 1923, [Convention date]. Wired wireless systems; thermionic amplifiers, detectors, generators, and modulating systems; calling systems and apparatus-A party-line carrier-wave system adapted for operation over power lines comprises means (a) for the safe coupling of the signalling apparatus to the high-voltage system (b) for enabling any station to call anv other station exclusively, or to send out a general call (c) for increasing the volume of signalling current under abnormal conditions, (d) for eliminating interference by harmonics of the power-line current or other extraneous disturbances. Fig. 1 shows the circuit arrangements at an operating station. The signalling apparatus is connected to the power lines 3 through coupling condensers 14 and a protective and interference-preventing network 13 comprising series and shunt capacities and inductances 19, 20, 21, 22, safety discharge devices 25, 26, 27 and fuses 24. Two different carrier frequencies are used, one f<1> for transmission by any station originating a call, and the other f<2> by the called station in replying. High and low pass filters HP11, LP12 for the two frequencies in question are interposed between the network 13 and the transmitting valves 7, 8, 9, and receiving valves 15, 16 respectively under the control of relays 40, 41. The setting of these relays is automatically changed through the contact 32 and relay 34 when a call is being made. Calling. The lifting of the telephone receiver first closes a relay 37 through the relay 34 and selector keys SK, SK<1>. The operator then actuates one of the keys SK corresponding to the station to be called, thus placing the condenser 38 in and out of the generator circuit, which has previously been energized through the closing of relay 36. This changes the frequency generated by the oscillator 7 alternately from f<1> to f<2>, but owing to the disposition of the relays 40, 41 only the frequency f<1> passes through the filter 12 to call the desired station. When the called station answers, the switch 4 may be thrown over to connect any subscriber 2 in circuit through a hybrid coil 5. The relays 42, 43 are not affected by an answering call, as they are short-circuited through relay 34. Response to call. The receiving tubes 15, 16 are normally energized and are in circuit with the line through the filter 12. Incoming impulses increase the plate current of rectifier 16 and close relays 42, 43. This in turn energizes relay 44, and causes the selector 17 upon receipt of the proper series of signals, to ring the bell 18. When the operator removes his receiver in answer to the call, the relay 34 is closed, but the relays 40, 41 and 37 do not operate because the inner contact of relay 43 is broken. The filter 11 therefore remains connected with the transmitting channel, and the filter 12 with the receiving channel. Idle station. If the wrong series of impulses are received the selector does not ring the bell 18 but lights a lamp 45 through the left-hand contact of relav 43. When the called station answers, high-frequency current is on the line and holds the lamp energized, thus warning the local operator that the line is busy. Emergency call. The key 46 is operated to call all stations by causing relay 43 to close a circuit directly through the bell 18. The selectors SK, SK<1> may then be employed to transmit signal impulses. Amplifier control. Normally the relay 60 is not operated, but if the amplitude of the signal waves rises above normal it brings into circuit an artificial line 61 which cuts down the received energy. Rectifier-detector control. For receiving the calling impulses the grid of the detector tube has the full negative voltage from the battery 62. When the operator answers the call, the relay 34 is operated and the right-hand outer contact reduces the applied grid potential to the optimum value for rectifying voice-modulated waves. Auxiliary transmitter. If line conditions are. bad, an additional amplifier 10 is brought into circuit by moving the switch 51 to its upper position, the plate circuit of the amplifier being energized through a motor generator 53 and the filaments through the relay 35. Fig. 2 shows an alternative method of coupling the signalling system to the power lines. Aerials 63, arranged either horizontally or vertically, are connected to the high tension lines 3, and are suitably insulated at 65. Coupling aerials 66 are placed on each side, as shown, and serve to transfer the signalling frequencies to and from the signalling circuit 67 and the high-voltage network. Fig. 3 illustrates one of several forms of coupling circuit which may be used in place of the circuit 13 in Fig. 1.