[电] cavity-tuned heterodyne frequency meter

kōng qiāng tiáo xié chuán sòng xíng pín lǜ jì ㄎㄨㄥ ㄑㄧㄤ ㄊㄧㄠˊ ㄒㄧㄝˊ ㄔㄨㄢˊ ㄙㄨㄥˋ ㄒㄧㄥˊ ㄆㄧㄣˊ lv4 ㄐㄧˋ