Transmission system for telephone communications or data transfer

A transmission system for telephone communications comprising at least two telephone sets, each incorporating microphone (9) and a receiver and/or loudspeaker (10), a telephone line connecting the telephone sets by two conductors in order to form a current loop, an alternating-current signal generator (2) and current-steering switch elements (3, 4;

• 6, 7 or 11) connected to the telephone sets and the conductors, arranged to steer the current to be routed during the positive half-cycles generated by the generator via the microphone circuit (9) of the first set and the receiver and/or loudspeaker circuit (10) of the second set as well as to steer the current during the negative half-cycles via the receiver and/or loudspeaker circuit (10) of the first set and the microphone circuit (9) of the second set, whereby voice transmission takes place by sampling the microphone signals of the interconnected telephone sets and transmitting the alternate signal samples superimposed on the generator signal so that the microphone signal of the first set is superimposed on the positive half-cycles of the generator signal while the microphone signal of the second set is superimposed on the negative half-cycles of the generator signal, characterized in that said current-steering switch elements are connected between a current loop comprising but two conductors, and a microphone circuit (9) and a receiver and/or loudspeaker circuit (10) at the telephone sets so as to prevent bidirectional current paths between the microphone circuit and the receiver and/or loudspeaker circuit within a single telephone set, while allowing only a unidirectional current path of the current loop through said circuits.