In radio communications systems, pertaining to a station that is completely shut down, i. E. , that is not transmitting any signal, not even an unmodulated carrier. 2. In a radio station, pertaining to a particular source of modulation, such as a specific microphone, that is disconnected, i. E. , is no longer capable of modulating the carrier. Note: The carrier may continue unmodulated or it may be modulated by another signal source.