lyhytaaltoviestintä

Lyhytaaltoviestintä, known in English as shortwave communication, refers to radio wave propagation in the high-frequency (HF) band, typically between 3 and 30 megahertz. These radio waves can travel long distances, often around the globe, by reflecting off the ionosphere, the electrically charged layer of Earth's upper atmosphere. This characteristic makes shortwave radio a vital tool for long-distance communication, especially in regions where terrestrial infrastructure is limited or absent.

The effectiveness of shortwave communication is influenced by various factors, including the time of day, season, and solar activity. During daylight hours, the lower frequency bands are better for communication, while at night, higher frequencies can travel further. Solar flares and other space weather events can significantly disrupt or enhance shortwave propagation.

Shortwave radio has been used for a variety of purposes throughout history. It played a crucial role in military communications during wartime, allowing for command and control over vast distances. International broadcasting has also heavily relied on shortwave to reach audiences worldwide, transmitting news, cultural programs, and music. Amateur radio operators, often called "hams," utilize shortwave for recreational communication, connecting with others across continents. Despite the rise of newer technologies, shortwave communication continues to be relevant for its reach, reliability in certain situations, and as a backup communication system.