Telecommunications circuitry for party line

摘要

The circuitry doubles the use capability of connection paths in dual subscriber connections. An add-on unit (VZ) at the exchange side is connected between the exchange point (V) and the connection path (AL). The add-on unit (VZ) includes a control unit (SE) which provides alternate voltages of opposite polarity at two outputs (A1,A2). Two diodes (D1,D2) are connected to these outputs (A1,A2). One of the diodes (D1) is connected to the a line and the other (D2) to the b line of the connection path (AL). A transformer (U1,U2) is connected in parallel with each diode (D1,D2). The other windings of the transformers (U1,U2) are connected to connections (V1,V2) for two subscriber devices in the exchange (V). Another add-on unit (EZ) is connected between the connection path (AL) and the user terminals (E). This unit (EZ) includes two diodes (D3,D4) which are arranged in opposite senses in series between the a and b lines. Both the b line connection (b') of the first user terminal (E1) or a lead to it, and the a line connection (a'') of the second terminal (E2) or a line leading to it, are connected to the node between the diodes (D3,D4). The a line connection (a') of the first terminal (E1) or a lead to it is directly connected to the a line. The b line connection (b'') of the second terminal (E2) or a lead to it is directly connected to the b line.