<p>In a powerline carrier control system, a powerline carrier control transmitter delivers an audio frequency voltage to the powerline carrier control receivers via a coupling unit and AC supply network. The coupling unit consists of a coupling transformer and an L-C combination which would normally insure that the network AC voltage is kept completely away from the powerline carrier control transmitter. In the system disclosed, back voltage is intentionally permitted and a supplementary AC voltage of line frequency is superimposed on the transmitter output voltage to buck the back voltage and thereby prevent current at the line frequency from the AC network from flowing through the transmitter. This simplifies and reduces the cost of the heretofore expensive components of the L-C combination.</p>
