There is disclosed an apparatus (10) for transmitting a communication signal across one or more pre-existing frequency channels or bands that carry a transmission signal. The apparatus comprises a memory for storing at least one pre-existing frequency channel or band together with information relating to a strength of the transmission signal carried by the at least one pre-existing frequency channel or band. A controller (24) is configured to generate a communication signal to be transmitted across at least one of the pre-existing frequency channels or bands at a strength sufficient to over-broadcast the transmission signal carried by said pre-existing channel or band. A mixer (26) is configured to receive each of the communication signals generated by the controller (24) and to combine said communication signals into a combined mixed communication signal (15). A transmitter (16) for transmitting the combined mixed communication signal (15) to be transmitted across the at least one pre-existing frequency channels or bands in replacement of, or in addition to, the transmission signal carried by the at least one pre-existing frequency channel.