Patent GB-143949-A (GB)
Title: Improvements in electric signalling systems, comprising amplifying or repeating apparatus
IPC: H04Q1/30
Filed: 1919-01-29
Abstract: 143,949. Western Electric Co., (Western Electric Co.). Jan. 29, 1919. Exchange systems; repeating systems.-Amplifying appuatus is controlled, independently of the current to be amplified, by means of a relay energized over the two sides of the line in parallel. In the system described, the circuit for heating the filaments 28 - - 31, Fig. 2, of the valve amplifiers A<1> - - A<4> is closed by a relay 3 energized when a plug is inserted at either or both exchanges in which the line sections terminate. The amplifiers are provided with a variable adjustment which is automatically modified when ring- ing-currents are received at the repeating-station, so that the amplifiers are enabled to repeat efficiently the ringing-currents. Ringing-current of ordinary frequency at the first exchange causes the transmission of ringing-current of higher frequency (e.g. 133 cyles) over the trunk line; this is amplified by valve relays at the repeating- station and determines, at the second exchange, the application of ringing-current of ordinary frequency to the connected line. The invention is described as applied to a system in which the circuit connected to the plug P, Fig. 1, is connected over a four-wire circuit to the circuit connected to the plug P<1>, Fig. 3, the four-wire circuit consisting of two separate transmission lines, each line being used for transmission in one direction only. Thus, transmission from exchange C to exchange E takes place over line L', amplifiers A<1>, A<2>, and line L<2>, whereas transmission in the reverse direction is effected over line L', amplifiers A<3>, A<4>, and line L<4>. At each exchange, the four-wire circuits are connected to the jacks J, J<1> by three-winding transformers 32, 33, 34 and 39, 40, 41. Artificial lines N, N<1> serve to balance the two-wire line with which the four-wire circuit is connected. When either or both operators insert the plugs P, P<1>, the relays 1 or 2, or both, are energized, and complete a simplex circuit over lines L<1>, L<2> for the relay 3, which completes the filament-heating circuits of the amplifiers. Speak. ing currents from the circuit of plug P pass over the transformer 32, 33, 34, circuit 5, transformer 22, and line L<1>, to transformers 23, 35 at the repeater station, where they are amplified by valves A<1>, A<2> and pass over line L<2> to transformers 26, 37, 39, 40, 41 at the second exchange and thence to the circuit of plug P<1>. Speaking currents originating in the circuit of plug P<1> pass over similar circuits associated with lines L<3>, L<4>. The armature of relay 55, Fig. 2, normally shunts the primary of transformer 35 by part of a resistance 8, this adjustment being suitable for the efficient amplification of speaking currents. 16- cycle ringing-current received over the circuit of plug P passes through the transformer 32, 33, 34 and energizes a relay 4, which closes the circuits of relays 51, 52. Relay 51 maintains the circuit of the normally energized relay 50 in case the relay 16 should be energized by ringing-current from the other exchange, and closes a circuit for the buzzer relay 18, the armature of which vibrates rapidly so as to break up the 16-cycle current supplied to it into 133-cycle current, which is connected over a transformer 53 and the armatures of relay 52 to the line L<1> to the repeater station. This ringing-current energizes a relay 7, Fig. 2, de-energizing a relay 54, which closes a circuit for a relay 55, which (1) opens the shunt around the primary of transformer 35, so as to ensure the efficient repetition of the ringing- current by the amplifiers A<1>, A<2>, and (2) shortcircuits the line L<4>, so as to prevent the possibility, ewing to imperfect balance of the transformer 39, 40, 41, of the amplified ringing-current passing back over lines L<3>, L<4> The amplified ringing-current passes over the line L' and transformer 26, Fig. 3, to energize a relay 9, thereby opening the circuit of a relay 56, which in turn energizes a relay 10 to connect low-frequency ringing-current to the circuit of plug P'. In a similar manner, ringing-current received over the circuit of plug P<1> energizes relays 11, 57, 58. high-frequency current from the buzzer circuit 13 passing over transformers 59, 42 and line L' to the repeater station, where it is amplified by valves A<3>, A<4> and passes over line L<4> to the first exchange, energizing relay 16, thereby opening the circuit of a relay 50, which in turn energizes a relay 17 to connect low-frequency ringing to the circuit of plug P.