VF=Variable Frequency 可变频率VF transmission音频传输VF key-sending按键音频信号发送VF telephone set可视电话机VFD without vent无排气管VFDvfemale graduates女大学生VF/DC converter音频直流转换器VF speed regulation交流变频调速VF telegraph bearer音频电报承载电路VF telephone circuit音频话路VF carrier telegraph音频载波电报