High Frequency (HF) (HF)
The radio-frequency band from 3 to 30 MHz.
Marine HF provides long-range voice, digital selective calling and data communications, principally by ionospheric sky-wave propagation beyond normal VHF and MF range.
Coverage varies with frequency, time, season, solar activity, antenna and interference. GMDSS equipment, watchkeeping, licensing and channel use depend on vessel and sea area; HF is not guaranteed to provide a stable link at every time and distance.









