Radio frequency (“RF”) transmitters include a digital-to-RF electronics module that receives an input data stream and outputs an RF signal, a switch having a first input port that is coupled to an output of the digital-to-RF electronics module, a second input port that is coupled to a matched termination, and an output port that is coupled to a communications network, a DC injection circuit that is configured to inject a DC signal at a first node on an RF transmission path that connects the output of the digital-to-RF electronics module to the first input port of the switch, and a DC monitoring circuit that is configured to sense if a DC signal is present on a second RF transmission path that connects the output of the switch to the communications network.