Patent GB-508941-A (GB)
Title: Improvements in and relating to electrical communication systems
IPC: H04B3/10
Filed: 1937-10-07
Abstract: 508,941. Automatic volume control; multiplex systems. TELEPHONE MANUFACTURING CO., Ltd., and PADDLE, L. H. Oct. 7, 1937, Nos. 27228/37 and 19130/38. [Class 40 (iv)] [Also in Group XXXV] In a system in which departure from the normal signal level by a predetermined amount due to line conditions &c. initiates the operation of a control device to restore the level to normal, the control device operates after a time delay which is substantially reduced during the controlling operation. The departure of the control device from normal may be increased when operation is initiated in order to permit correction of the initial predetermined departure, or the connecting device may be allowed to overrun to the required extent, e.g. by slow-to-release control relays. In one system described, Figs. 1 and 2, departure from normal by a value which is a fraction, e.g. of the predetermined amount, prepares the control device for operation, a further departure to the predetermined amount effects control to restore the level, or a natural reduction to normal restores the control device to normal. A simpler arrangement, Fig. 3 (not shown), does not embody this feature but a relay operated in response to a departure in one direction disables the relay responsive to a departure in the opposite direction. The invention is described with reference to a multiplex system comprising audio-frequency telephony, a double-band telegraphic channel including a control frequency, and a double band carrier telephone channel, the channels occurring in this order. The audio channel passes over filters F1 and a two-way repeater with volume control potentiometer may be inserted at X. The east carrier telephone channel passes over F2, F3, F5 and amplifiers controlled by potentiometers P1, P2, the west channel being indicated by similar references with suffix a. The east telegraphic and control channel passes over F4, F7, potentiometer P3 and amplifier A3, from the output of which the control frequency passes to amplifier A5 and filter F9, the telegraphic channel being completed over P4, F8. A similar telegraphic and control channel is provided for west traffic. Potentiometer P3 and potentiometers in other east channels are operated by the east control circuit and where a number of lines are subject to similar conditions, one control in each direction may serve for all of them. Control arrangements. The portion of Fig. 1 within the chain line is shown in full in Fig. 2. The output of potentiometer P3 after push-pull amplification at V1, V2 is divided, the telegraphic signals being passed over 11 whereas the control frequency is amplified at V3, subjected to a narrow band filter F9, and after further amplification and rectification is applied to control the anode current of pentode V5, a master relay K being operated to condition the control circuits providing a predetermined minimum of control frequency is present. The control circuit proper comprises amplifier V6, rectifier 13, delay network 14, 15 and a bridge comprising pentode V7, polarized relay P, and resistances 16, 17, 18. Normally, the armature of P floats between its contacts. Assuming that the predetermined change requiring compensation is 4Db, an increase of 2Db causes relay P to make contact at p1, whereupon relay X operates followed by A and B which lock up, resistance 17 in the bridge equivalent to 2Db being short-circuited by A to restore the bridge so that P and X restore to normal. When a further increase of 2Db occurs, P and X operate as before but are now followed by C and E. Relay A is released by E so that resistances 16 and 17 representing a change of 4Db are now included in the bridge circuit to unbalance the bridge still further. Relay C starts the motor M which drives potentiometer P3 and the potentiometers of other channels until normal level is restored whereupon P, X, C, E and B restore, the motor stops and the control circuit assumes its normal condition. During the controlling 'operation, resistance 14 of the delay network is short-circuited by E. If the original 2Db increase has been followed by a 2Db decrease, contacts p2 would have operated Y whereupon A and B would fall back, and the bridge circuit restored to normal followed by the release of Y. In this case F is not operated since B is energized. If there is an initial decrease of 2Db followed by a further decrease of 2Db the lower set of relays Y, F, D, H, G, J operate in a manner similar to that described for the upper set except that H reverses the motor, the bridge being restored by F after the first decrease and unbalanced by 4Db by F and D after the second decrease. If the potentiometers are driven to the limit in either direction, a switch LS opens the motor circuit and operates an alarm B over key KS. Alternatively, the potentiometer drive may include a slipping clutch. The potentiometer arms may be adjustably mounted for individual setting, and with key T.K thrown, adjustments may be effected without operating the relays.