Abstract

A transmitting station is connected to a receiving station by a two-wire line via which the supply current required for operating the transmitting station is transferred from the receiving station to the transmitting station. The transmitting station comprises a supply circuit including a voltage regulator for maintaining the operating voltage of the transmitting station constant and an energy store for compensating current and/or voltage fluctuations. Via the two-wire line a signal current, variable between two limit values, is further transferred from the transmitting station to the receiving station. This signal current consists of the supply current for the transmitting station and a supplementary current determined by the transmitting station. For transfer of the communication information between the transmitting station and the receiving station, a symmetrical communication current is superimposed on the signal current. The communication current is superimposed on the current flowing from the two-wire line into the supply circuit of the transmitting station.