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, is characterised in that 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 that produced by current ( 1 ) of the conductor in said coupling unit, and thereby avoiding the saturation of the magnetic care ( 30 ) without adding insertion loss. In general it is applied to communication systems which require the injection of a radiofrequency signal on a conductor, and in particular in systems which use the electricity grid as the transmission medium.