Patent GB-153357-A (GB)
Title: Improvements in electric signalling systems
IPC: H04B3/14
Filed: 1919-07-24
Abstract: 153,357. Western Electric Co., (Western Electric Co.). July 24, 1919. Duplex telegraphs; receiving systems and apparatus; repeating systems and apparatus.-A distorted signal impulse with a slowly rising wave front is restored to a form having a steep wave front by the provision of distortion-correcting circuits placed between the cable terminal and the receiver or another line. The correcting-circuits comprise series elements, of which the impedances decrease with the frequency, and shunt elements, of which the impedances increase with the frequency of the received impulses. The correcting- circuits add to the received impulses derivatives of this impulse and the restored impulse is amplified by means of thermionic valves; or the signal impulse and its derivatives are amplified separately to varying degrees and aggregated to constitute the amplified and restored impulse. In the duplex system shown in Fig. 1, an inductive shunt 6, 7, 8 and 9 is placed across the terminals of the cable 5 and the artificial line 12, and between this shunt and the primary winding of a transformer 18 are placed shunt elements 14 and series elements 13. The secondary winding of the transformer 18 is connected across the grid and filament of a valve amplifier. Several amplifiers, connected in cascade, may be employed as shown, and the plate and filament circuit of the last contains a receiver 30 or may be connected to a second transmission line. If the curve A1 Fig. 4, represents the wave form of the arrival current passing through the inductive shunt 6, 7, 8, 9, a voltage which is approximately the first derivative B of the curve A is developed across the terminals 16, 17 of this shunt. The application of this voltage to the first series element 13 develops a current which approximates to the second derivative C of the curve A. Similarly the voltage across the first shunt element 14 approximates to the third derivative D of the curve A, and the current through the second series element 13 approximates to the fourth derivative E of the curve A. There will thus be produced at the terminals of the last section a voltage which produces, together with the other currents passing through the series elements 13, a current approximating in form to the curve H, Fig. 3, having a steep front which requires a time t1, less than the time required for transmitting a dot, to reach its maximum value. In order that the transformer 18 shall not distort the restored signal current by an amount greater than that shown by the curve I, it is arranged that the ratio of the inductance in henries to the resistance in ohms of the primary winding shall be greater than the time in seconds which covers the maximum number of consecutive impulses of the same polarity in the code employed. To prevent fluctuations of potential at the terminal 32 of the amplifier system, due to the operation of the transmitter 11 and the ground connexion 31 of the amplifier system, a grounded shield 33 is placed between the primary and secondary windings of the transformer, and the amplifier is further shielded from stray fields by enclosing it in a copper-lined iron box. The series elements 13 and shunt elements 14 may be formed of various combinations of inductances, resistances, and capacities. In the modification shown in Fig. 2, the inductances 6, 7 form the primary winding of the transformer 18, and these may be shunted by elements 14. The secondary winding of the transformer 18 is connected to the first valve of the amplifier system, and between the valves of this system series and shunt elements 13, 14 are inserted in order that the derivatives may be amplified after they are obtained. In the arrangement shown in Fig. 14, inductive arms 36, 37 are shunted by the primary winding 40 of a transformer 41. The secondary winding 42 is connected to the first valve 43 of an amplifier system. The output circuit of the valve 43 contains a potentiometer 55 by means of which it is connected in a variable manner to the valve 44 of the system A and to the valve 59 of a second system B. Between the valve 59 and a second valve 60 of the system B a transformer 70 is introduced by means of which the first derivative of the arrival current is supplied to the valve 60. A third system C may be arranged to supply an amplified second derivative, and the amplified arrival current and its first and second derivatives are supplied to the receiver 69 or a second transmission line. In the modification shown in Fig. 15, the amplifier systems A, B are connected to line by transformers 41 and the output circuits of these systems are connected by transformers 71 to the circuit of the receiver 69 to produce in this circuit current waves having the forms of the arrival current and its first derivative. The secondary winding of the transformer 70 between the valves 59, 60 of the system B is connected to the first valve of a system C having series and shunt elements so that this system supplies amplified second and third derivatives to the receiver circuit through the transformer 71. In a further modification, series and shunt elements are placed between the line and the primary winding 40 of the transformer 41, Fig. 14, between the valves 59 and 60 of the system B, and between the valves of the system C in order that the arrival current and its first five derivatives may be supplied to the receiver circuit. In the arrangement shown in Fig. 17, the output circuit 73, 74 contains resistances r' - - r' connected across the output circuits of valve amplifiers A' - - A<7> respectively. The line 72 is connected to the input circuits of valve amplifiers a', b<1>, and A' through a transformer 75. Additional amplifiers a<2>, a<3> and auto-transformers 78, 80 and 82 are provided in order that the voltage drops across the resistances r', r<1>, r<3>, and r<2> may be proportional to the first, second, third and fourth derivatives respectively of the arrival curve A shown in Fig. 4. Additional amplifiers b<2>, b<3> and circuit networks 84, 85, 86, and 87 are provided in order to impress an aggregate voltage drop across the resistances r<5>, r<6>, and r<7> proportional to the arrival curve A, Fig. 4. The amplifiers employed in the arrangement shown in Fig. 17 each comprise a thermionic valve 88, Fig. 18, the grid and filament of which are connected by a high resistance 89, while the input circuit contains a large capacity 90. In the modification shown in Fig. 19, voltage drops proportional to the first, second, third, and fourth derivatives of the arrival current are impressed across the resistance r<8> by means of amplifiers a', a<2>, a<3>, and A' and distortion networks 78<1>, 80<1>, and 82' containing resistances 88; while additional amplifiers b<1>, b<2>, b<3>, and A<2> and circuit networks 84<1>, 85'; 86<1> and 87<1> are provided in order to impress an aggregate voltage drop across the resistance r' proportional to the arrival curve