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High frequency (HF) is an electromagnetic frequency defined by the International Telecommunications Union (ITU) for radar and radio communications. It operates in a range of three to thirty MHz and as the wavelengths spread over ten to one hundred meters, it is also known as decameter wave and designated as band 7. High frequency is highly popular among amateur radio, military and government communications, radar communications and global maritime distress and safety system communications.
The International Telecommunications Union radio regulations have designated each frequency range of the spectrum with a band designation and each frequency range has different functionalities as well as behavior. The high-frequency spectrum, according to the ITU radio regulations, has been shared with government, military and civil authorities of all countries. One of the salient features of high-frequency waves is the ability to reach intercontinental distances by traveling beyond the horizon and along the Earth’s curves. Therefore, direct long-distance communication is possible with the help of high-frequency waves. However, variable conditions such as season, sunspot cycles, proximity to the solar terminator for both sender and receiver equipment, polar aurora and solar activities can limit the use of the high-frequency spectrum. In other words, variable day-to-day ionosphere conditions affect the high-frequency spectrum.
Less costly equipment is required for high-frequency communication compared to other frequency modes. High frequency allows for quicker and direct communication techniques. With a combination of other techniques such as adaptive systems, high-frequency communications can be as effective as satellite and telephone communications.
Drawbacks of using the high-frequency spectrum are limited bandwidth and lower reliability compared to other frequency bands.