voice-frequency signalling current [电子] 音频信号电流

voice frequency signalling current 音频振铃电流

single current signalling 单向电流信号

direct current signalling DC signalling 直流信令DC信令

direct current signalling code 直流信号标志

alternating current signalling AC signalling 交流信令AC信令

direct-current signalling [通信] 直流传信

double-current signalling [通信] 双流传信