An apparatus comprising a signal transformer coupled to a power line and a signal transmission, reception, or detection circuit. A sensor is configured to be responsive to the power line current or magnetic flux generated in a ferrite core of the signal transformer. When the sensor indicates that the flux generated by the power line current mat cause an attenuation of the signal strength, a second circuit generates a current through a flux cancelling winding that cancels at least some of the flux generated by the power line current.