Abstract: A circuit (100) for coupling an amplifier (1) in an electrical power distribution system with the amplifier electrically and physically isolated from a power line of the system. The amplifier generates arbitrary signal waveforms injected into the power line. A transformer (T1) has a primary and a secondary side with the amplifier located on the primary side and the secondary side connected to the power line. A resistor (R1) series connected with the primary side of the transformer is sized to accommodate a minimum load impedance of the amplifier and minimize power dissipation. A resonant circuit interposed between the secondary side of the transformer and the power line has values for a capacitor (C1) and an inductor (L3) forming the resonant circuit chosen to peak the amplitude of the arbitrary signal waveform at the frequency of a waveform propagated through the power line.