416,867. Wired wireless systems. STANDARD TELEPHONES & CABLES, Ltd., Connaught House, Aldwych, London.-(Western Electric Co., Inc. ; 195, Broadway, New York, U.S.A.) March 23, 1933, No. 8779. [Class 40 (v).] In a telephone or other transmission system in which repeater stations are included at intervals along the system, these stations are unattended and signals are sent automatically from the unattended station to a main or terminal station to indicate the condition of the repeaters as regards their normal or emergency power supply and to indicate the proper or abnormal working of the automatic gain control mechanism. The system is particularly intended for multiplex carrier current telephony, which requires shorter intervals between repeaters than in the case of ordinary telephony. Fig. 1 shows the system as a whole with lines 1, 2 extending from a main station M to a repeating station R. A pilot line 5 is used in connection with the gain regulator 6 which by rotating a control shaft adjusts the gain or loss. The normal and emergency power supply is shown at 11, and the condition of this supply as well as of the gain control regulator 6 operates signaltransmission mechanism 7 which by a special line 8 (or by compositing some of the lines 1, 2) operates a switch 9 to select a signal 10 at the main station M. Automatic gain control. The pilot wire 5, Fig. 3, lies in one arm of a bridge 25-28, one diagonal of which is provided by a battery 38 and the other by a galvanometer 23. One terminal of the battery 38 is connected to a rotary arm 33 moving over resistance studs so that one section of the resistance 29 is in bridge arm 28 and the other section in the bridge arm 27. The arm 33 is rotated by a motor 30 and on its shaft 12 are also fixed other arms which adjust the gain or loss in the repeaters, preferably by varying resistances 21, 22 in an attenuation network 20 of the kind described in Specification 202,284, [Class 40 (iii)]. When the pilot wire resistance varies with change of temperature &c. the bridge is unbalanced, and the galvanometer contact 40 or 41 is closed, energizing relay 31 or 32. Under normal conditions a relay 36 is energized over a contact 48 on a cam 42 and connects a battery 44 through a contact on a normallyclosed master key 35 to the field winding 45 of the motor 30. The relays 31, 32 serve when energized to connect the battery 44 to the armature of the motor 30 to start it up in one or the other direction. Rotation restores the bridge balance by moving the arm 33 and also adjusts the gain by varying the resistances 21, 22. As the arm 33 is progressing from one contact to the next, the operative relay 31 or 32 is held energized by a cam-operated contact 47 which only opens again when the arm 33 has centred on its next stud. Various signals (a)-(d) to indicate the condition of the apparatus are sent by earthing conductors 52, 55, 56, 57 respectively. (a) Unbalance of the bridge in either direction closes contact 49 or 50 and operates relay 51 to earth the line 52. (b) When the arm 33 reaches either extreme position cams on the disc 42 open the contact 48 to release relay 36 and to earth the line 55. (c) Failure of the bridge battery 38 releases a relay 37 and earths the line 56 ; and (d) an excessive want of balance in the bridge causes a differential relay 43 to operate to earth the line 57. Power supply apparatus. During normal working plate voltage for the amplifiers is supplied from a battery 67 which is maintained charged by a rectifying plant 66 fed from A.C. mains 60, which also supply cathode heating current through leads 69, 70 and transformer 72. On failure of the mains 60, or on the occurrence of excess or under voltage, marginal relay 63 or 64 connects a relay 65 across the battery 67. The relay 65 disconnects the supply mains 60, and also connects the battery 67 across a relay 77, and a slow-acting relay 78. The relay 77 disconnects the battery 67 from the charger 66 and connects it to a dashpot relay 79 and to a motor-generator 82 provided with an automatic starter 81. The generator 82 supplies current to a relay 71 which when the voltage has reached normal operates to connect the generator output to the transformer 72 for supplying heating current to the amplifiers. The relay 71 also opens a contact in the circuit of relay 78, but should the motorgenerator fail to start, the relay 78 slowly operates and at its lowermost contact closes the circuit of a solenoid 80. As its core is attracted a cam 97 thereon slowly wipes across a spring contact 96 to connect the gas engine starter 99 across the battery 67 for a limited time.. After starting, centrifugal contacts 94 opens the circuit of relay 80, and the engine drives an alternator 100 which energizes relay 83 and on developing its full voltage connects itself to the charging-set 66 and to the heater transformer 72 ; it also de-energizes relay 77 and re-connects the battery 67 to the output terminals of the charging-set 66. If the motorgenerator 82 starts up normally, it is replaced by the gas-engine after the expiration of a time, say, 15 minutes, determined by the dashpot of the relay 79. When this is fully operated, its contact energizes the relay 80 and starts up the gas engine 84, which operates as before to energize relays 83 and 77. The latter disconnects the battery 67 from the motorgenerator 82, thus stopping this machine, releasing the relay 71 and connecting the transformer 72 to the leads 69, 70 which are now supplied by the alternator 100. If the voltage on the supply leads 60 returns to normal during the operation of the gas engine 84, relay 65 is released so shorting the ignition circuit of the engine at its lowermost contact. The stoppage of the engine releases relay 83 and restores all circuits to normal. Should the voltage return to normal during operation of the motorgenerator set 82, release of relay 65 results in the release of relay 77, which stops the motor generator and connects the battery 67 to the charging-set 66. The condition of the supply apparatus is signalled to the main station by earthing a series of leads 87, 88, 101 and 103. When lead 87 is earthed by energization of relay 77, its signal indicates that the mains supply has failed and that the first reserve power -the motor generator-is being put into service. Lead 88 is earthed by operation of relays 77 and 78, and the corresponding signal indicates that the motor-generator has failed to start. Lead 101 is earthed on energization of relay 83, and its signal indicates that the gas engine is in action. If the gas engine fails to start in response to the relays 79, 80, a signal is given by earthing a lead 103 through a contact on relay 83, contact 92 of relay 79 and contact 102 of relay 80. Signal transmitting circuits. The earthing of any one of the eight lines 52, 55, 56, 57, 87, 88, 101, 103 causes the stepping forward of the arm C to a selected contact, and the arm B on the same shaft sends impulses to the line 8 which operate a selector 9, Fig. 1, to give a corresponding signal 10 at the main station M. If, for instance, line 52 is earthed, relay 116 is energized and by earthing its left-hand contact closes a circuit for the stepping-magnet MM through the back contacts of all the relays 115-111 in series. The arms A, B, C are thus stepped round until they rest on their sixth contacts. The arm 9 at the main station moves in step, and is arranged in known manner so that the lamp 10 is lit only when the arm comes to rest. When earth is removed from the line 52, relay 116 releases and earths all the contacts of the arm A, which is therefore stepped round with arms B, C and 9 to the zero position. Each repeater station has its own signal line 8, selector 9, and signal bank 10.