国际遇险呼救频率 [水运] [通信] international distress frequency

遇险呼救频率 distress frequency ; distress frequencies

遇险呼救信号 distress signals

无线电话遇险呼救频率 radio-telephone distress frequency ; telephone distress frequency

国际遇险呼救电码 [水运] [通信] international distress code

低功率遇险呼救发信器 low power distress transmitter