GB519748A - Improvements in or relating to radio-telephone circuit arrangements - Google Patents

Abstract

519,748. Two-way transmissions. STANDARD TELEPHONES & CABLES, Ltd., and MEERS, R. A. Sept. 30, 1938, No. 28485. [Class 40 (iv)] [Also in Group XL] In a system in which a radio-telephone terminal station has four-wire line connections to extension stations, a feed-back path from the transmitting circuit to the receiving circuit is provided in the terminal station to supply an artificial side-tone to the extension subscribers and to permit the terminal operator to monitor on both circuits by means of a permanent connection to the receiving circuit. In the system shown, an extension subscriber, Fig. 1, has a local side-tone circuit-over condensers C1, C2. On lifting the handset to make a call, hook-switch contacts g operate and relay A energizes to light calling lamp LS1 and to sound a gong G through relay B. When the terminal operator, Fig. 2, inserts the double plug PI, the local side-tone circuit is replaced by one through condensers C3, C4. The operator communicates with the subscriber by throwing key K2 upwards energizing relay C which transfers one of the operator's receivers OR1 from the receiving circuit RL to plug PJ1, the other receiver OR2 being permanently connected to the receiving circuit. At the same time, the operator's microphone is fed over retard L1 and connected over terminals 3 and 7 of transformer T1 to plug PJ2. Movement of key K2 downwards connects the subscriber's transmitter over amplifier AMP1 to the radio transmitter, and part of the speech acts through a control circuit SC to render a feed-back circuit over a "silent-coil" set T3, T4 operative and to render the receiving circuit inoperative by means of a further "silent-coil" set T5, T6. Each of these coil sets presents high impedance with the cross-connections as shown at T5, T6 but has low impedance when terminals 3 are connected together (or both' to ground as .shown). The relay in the control circuit operating contacts sc may also control the connections between the transmitter or receiver and the aerial. When the subscriber, Fig. 1, hangs, up, lamp LS1 is lit over contacts 13, a 1, j 23, but the gong is not sounded. To call the subscriber, key K1 is operated, connecting battery over the tip and sleeve of plug PJ2 to a direct-current bell D. The operator may talk to the radio-transmitter by operating key K3, coil 4, 5 only of transformer T1 being employed in order to give the same speech level as for a subscriber.