långväg

Långvåg, or longwave, refers to the radio frequency band from about 30 kHz to 300 kHz, as defined by the International Telecommunication Union. It lies below the medium-wave (MW) band and above very low frequency services. The exact limits can vary by country, but the commonly cited ITU range is 30–300 kHz.

Longwave signals propagate primarily as ground waves that travel along the Earth's surface, providing regional coverage with relatively consistent reception over long distances on land and at sea. At night, certain frequencies within the band can also reach farther distances through skywave propagation, when the signal is reflected by the ionosphere. The long wavelengths involved require large antennas and typically high-powered transmitters, with stations often using tall vertical antennas and power levels ranging from tens to hundreds of kilowatts, and in some cases higher.

Historically, långvåg has been used for broadcasting, time signals, and navigational beacons. In Europe and parts of Asia, longwave radio provided broad-area services before the widespread adoption of FM and digital broadcasting. The German time signal transmitter DCF77 at 77.5 kHz is a well-known example of a longwave time signal. In many regions, longwave broadcasting has declined or been discontinued in favor of newer technologies, but some time-signalling, maritime, and specialized services continue to operate on the band.