Abstract: A transmission bridge comprising two alternating current circuits having a non-inverting signal input, an inverting signal input and a signal output, the non-inverting signal inputs being coupled to associated connecting terminals for the connection of a subscriber's line, the inverting signal inputs being connected to those terminals to which the non-inverting signal inputs of the other alternating current circuits are coupled, the outputs being coupled to the connecting terminals via supply resistors for preventing the anti-phase signals such as speech signals, present at the terminals, from being attenuated and for attenuating by means of the supply resistors in-phase signals, such as noise signals induced in the subscriber's line, present at the terminals.

Abstract: A bridge circuit comprising an isolation transformer having six primary windings which are connected so that the voice currents do and the supply currents do not generate, for either direction of current flow, a resulting flux in the core of the transformer. The bridge comprises two transistor circuits which prevent the voice currents from flowing through a supply source connected to the bridge and also balance the bridge circuit so that the influence of longitudinal noise signals which are produced in a transmission line connected to the bridge circuit are suppressed. The direction of the feed current in the transmission line can be reversed by means of the transistor circuits.