Hybridschaltung eines Übertragungssystems

Control circuit for automatically controlling the balance impedance (Zb) of a transmission hybrid. A unidirectional device (A1/Ro) and a detection device (A3, AND gate) detects when the reception port (3) receives signal exclusively from the four-wire part. It is only then that whether the balance impedance is correctly adjusted or requires adjustment can be checked. At such a check instant (the AND gate is then "high"), the balance impedance can be adjusted by a control device (A2, S) in such a way that any crosstalk signal at the transmission port (1) (originating from the reception port) is eliminated.