HF

High frequency (HF) is the range of radio waves between 3 and 30 megahertz (MHz). Frequencies immediately below HF are denoted medium frequency (MF), while the next band of higher frequencies is known as the very high frequency (VHF) band. The HF band is a major part of the "shortwave" band of frequencies, so broadcast stations using these frequencies are often called shortwave stations. Because radio waves in this band can be reflected back to Earth by the ionosphere layer in the atmosphere – a method known as "skip" or "skywave" propagation – these frequencies are suitable for long-distance communication across intercontinental distances and for mountainous terrains which prevent line-of-sight communications. The amateur bands included in HF are 80 meters (m), 60 m, 40 m, 30 m, 20 m, 17 m, 15 m, 12 m, and 10 m. Although 6 meters is a VHF band, it also sometimes exhibits skywave propagation similar to that normally found on HF.

In addition to amateur radio, HF is used by international shortwave broadcasting stations (3.95–25.82 MHz), government time stations, weather stations, CB radios, and some aviation radios, among other uses.

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