High Frequency (HF) Share definition Flag Frequencies between 3 MHz and 30 MHz (3 Mega Hertz and 30 Mega Hertz). Used by governments, ships, radio stations and amateur radio operators. I decided to use the High Frequency (HF) radio last night and try my luck at reaching Japan. High Frequency (HF) by Tomorrow's World October 20, 2009 Get the High Frequency (HF) mug.