DE2736136

Hybridless bidirectional transmission networks typically include telephone line coupling transformers and unidirectional amplifiers for enhancing outgoing and incoming signals. Unwanted signal components in the outgoing direction, caused by cross coupling via the transformer of incoming signals, are minimized by employing a canceller network in circuit with the incoming and outgoing amplifiers. The canceller network has a complex transfer characteristic to compensate substantially for complex impedance components of the coupling transformer and 2-wire transmission facility and to generate a signal which is substantially a replica of the unwanted outgoing signal components. The replica signal and unwanted signal components are algebraically combined in the outgoing amplifier effectively to eliminate the unwanted signal components from the outgoing path. In a first embodiment the canceller network has an attenuation versus frequency characteristic yielding a prescribed second-order complex transfer characteristic while in a second embodiment the canceller network has an attenuation versus frequency characteristic yielding a prescribed fourth-order complex transfer characteristic. In the second embodiment values of predetermined pole-zero pairs are selectively adjustable to match impedance components of different 2-wire transmission facilities.