Abstract: In a system for transmitting information on an a.c. line from a transmitter unit to a receiver unit which is connected to the line at a great distance from the a.c. source supplying said line than the transmitter unit, information is transmitted on one of the phase conductors of the line in a form of a series of short-duration pulse-like amplitude reductions in the alternating voltage waveform on said phase conductor during one and the same half cycle of the waveform, whereat the pulses are mutually arranged in the pulse series to form a binary code word representing the desired information.