CONFERENCE SYSTEM WHEREIN TRANSMITTING AND RECEIVING TERMINALS ARE SEPARATELY CONNECTED TO A TALKING BUS

1,153,671. Conference circuits. WESTERN ELECTRIC CO. Inc. 4 Aug., 1966 [6 Aug., 1965], No. 34948/66. Headings H4K and H4R. In a system comprising a number of line circuits with transmit and receive terminals T1, R1 &c. and a common talking bus, a TDM arrangement is employed whereby the transmitters are connected during successive time slots to the bus while the corresponding receivers are disconnected from it, so that the effect of echoes is eliminated. Each transmitter is connected to the bus through a sampler, while each receiver is connected through an integrator. In a 20-line system, Fig. 1, the connections are controlled by a 20-stage ring counter operating at a 200 kc. rate so that each transmit terminal is sampled at a 10 kc. rate. Two such systems may be coupled together, Fig. 2 (not shown), during one time slot of each to provide a 38-line system. Further, a 380-line system may be obtained by employing a central 20-line system S0 Fig. 3, to couple together twenty 20-line systems such as S1, S6, S11, S16, each serving 19 line circuits. Detailed circuits are described of the ring counter and of the transmit and receive portions of the line circuits, each of which includes a semi-conductor switching device. The common bus is grounded momentarily at the end of each time slot to dissipate any residual signal after each sampling operation, and thus improve echo-suppression.