disclosed are systems and methods for transmitting a signal . an exemplary system includes a circuit for a system having a signal source , an antenna , and a cable coupled to the signal source and the antenna . the circuit includes an amplifier having an input for coupling to the cable , and output for coupling to the antenna , and a control input . the amplifier varies output power responsive to a signal on the control input . a detector detects a dc bias on the cable . the detector has an output coupled to the control input of the amplifier .