The invention relates to a device for improving the transmission properties of a bundle of electrical data lines, particularly of a bundle of copper twin wires, and to a system for transmitting data that is provided with a device of this type. Said device comprises at least one adaptive filter, which generates an output signal for correcting the signal transmitted on a first data line. At least one signal tapped by a second data line or an external signal is used as a reference signal for the adaptive filter, and the corrected signal transmitted on the first data line is used as an error signal for the adaptive filter. According to the invention, the device is situated in the transmission path whereby improving the transmission properties of the cable independent from the switched-on transmission units and employed transmission techniques, particularly in the event of high bit rate transmission.