Lyhytaalt

Lyhytaalt is a Finnish term used to describe the shortwave portion of the radio spectrum and the services that operate within it. Shortwave typically refers to frequencies roughly from 3 to 30 MHz, a range that allows signals to travel long distances by reflecting off the ionosphere. Propagation in the lyhytaalt band is highly variable, influenced by solar activity, time of day, season, and atmospheric conditions.

In practice, lyhytaalt services include international broadcasting, amateur radio, time signal transmissions, and certain maritime and aviation communications. The long-range reach of shortwave makes it suitable for reaching distant or geopolitically isolated audiences, as well as for emergency communications where other infrastructures are unavailable. Transmissions are produced with a range of equipment, from large, high-power transmitters to smaller consumer and vintage sets, while reception spans from traditional portable radios to modern software-defined receivers.

Regulation of lyhytaalt operations is governed by international bodies such as the International Telecommunication Union (ITU) and national communications authorities. Frequency allocations, licensing, and permitted power levels vary by country and service type, with operators required to comply with international treaties and national rules.

History shows lyhytaalt playing a major role in early radio development and international broadcasting in the 20th century, including wartime communications and global news dissemination. While satellite, cable, and internet services have reduced its dominance, shortwave remains valuable for hobbyists, some broadcasters, and emergency communication networks.

Today, lyhytaalt activity continues in many countries, supported by diverse equipment and a dedicated community of listeners and operators.