GB1282190A - Operator's four-wire telephone set - Google Patents

Abstract

1282190 Operators set; two-way transmission systems INTERNATIONAL STANDARD ELECTRIC CORP 24 Sept 1970 [30 Sept 1969] 45507/70 Headings H4K and H4R An operators set PO can be coupled to incoming and outgoing four wire lines L1, L2 so that in each transmission path there is an input amplifier AE connected through an impedance R1, R2 to an output amplifier AS connected through an impedance R1, R2 to an output amplifier AS connected through further impedances R3, R5; R4, R6 to a receiver and transmitter respectively. The feedback amplifiers have low input impedance and thus there is no coupling between the two input impedances for the amplifier and thus no coupling between the two directions of transmission. By the operation of switches do 1-dc4, ds1, ds2 and contacts in CC the operator can, (a) speak to both parties, (b) speak only to one party or (c) monitor a call. In all cases the connection is made through CC by closing switches dc1-dc4 and opening switches ds1, ds2. (a) Speak to both parties: contacts g1, g2 and d1, d2 are closed to connect both lines through the amplifiers via transformers T1-T4. Shuntin resistors ra1-ra4 are used to match the operators set PO to the line impedance. (b) Speak to one party: contacts g1, g2 are operated to speak to party L1 leaving party L2 terminated on impedances Z1, Z2 through contacts d2, SU2 and d1, SU1 respectively. To speak to party L2, contacts d1, d2 are operated leaving line L 1 terminated on impedances Z 1, Z2. (c) Monitor a call: contacts SU1, SU2 are operated to connect line VA1 to transformer T2 and line VA2 to transformer T4 so that the conversation can be heard in receiver EC. Matching resistors ra2, ra4 are disconnected by opening contacts SU3, SU4. All impedances R1-R8 have the same value.