Process and device for compensating the low frequency magnetic field in an inductive signal coupling unit. According to the invention the coupling unit comprises a ferromagnetic core (30) which encloses a conductor through which a low frequency current (1) is circulating in order to inject thereon a high frequency signal. Current (1), circulating through the conductor or the magnetic field (3) produced in the coupling unit, is detected, and a compensating current is obtained based on the value obtained in the detection carried out, and the compensating current obtained in the coupling unit is injected through a low pass filter (9) to produce a magnetic field (4) equal and opposite to the produced by current (1) of the conductor in the coupling unit, and thereby avoiding the saturation of the magnetic core (30) without adding insertion loss. In general the invention is applied to communication systems which require the injection of a radio frequency signal on a conductor, and in particular in systems which use the electricity grid as the transmission medium.