Longwave

Lore & Background

Longwave is a historic term from the early 20th century, when the radio spectrum was divided into long, medium, and short waves. Its definition remains imprecise: it may refer to wavelengths longer than 1000 m (frequencies below 300 kHz) or, in some contexts, up to 520 kHz.

In ITU Region 1, longwave broadcasting occupies 148.5–283.5 kHz, with carrier frequencies set at exact multiples of 9 kHz from 153 to 279 kHz under the Geneva Frequency Plan of 1975. Exceptions include Mongolian transmitters, which operate 2 kHz above the recognized channels, and the former Europe 1 in Germany, which retained prior spacing until 2019. Until the 1970s, some stations in northern and eastern Europe and the Soviet Union used frequencies as high as 433 kHz.

Propagation relies primarily on ground waves, which follow the Earth's surface and suffer less attenuation at lower frequencies, allowing reception up to 2000 km. Skywave propagation via ionospheric reflection can extend beyond 3000 km.

Very low frequencies (below 30 kHz) can penetrate saltwater to depths of hundreds of feet, enabling military communication with submerged submarines. The band also hosts non-directional beacons for navigation (190–1750 kHz), time signal stations (e.g., WWVB on 60 kHz, DCF77 on 77.5 kHz), and amateur radio allocations (135.7–137.8 kHz). In North America, unlicensed LowFER operation is permitted on 160–190 kHz with limited power and antenna height.

Historic longwave transmitters include the Alexanderson alternator at SAQ in Grimeton, Sweden, which still makes demonstration transmissions on 17.2 kHz. Many countries have ceased longwave broadcasting due to low audiences, lack of receiver support, interference, and high electricity costs. Russia closed all its LW transmitters between 2014 and 2015; the BBC ended Radio 4 on 198 kHz in June 2026. As of 2023, the only remaining longwave stations were in Romania, Poland, Algeria, Morocco, and Mongolia.

Reader's Guide

Longwave's significance lies in its unique propagation characteristics and specialized applications. Ground-wave propagation provides stable, predictable coverage over large geographic areas, making it ideal for time signal broadcasts used by radio-controlled clocks.

Because longwave signals travel along a constant surface path, the time delay from transmitter to receiver is essentially fixed for a given location, allowing accurate timekeeping with a single correction factor. This contrasts with medium- and short-wave signals, whose skywave paths vary with ionospheric conditions. Time signal stations such as WWVB, DCF77, JJY, RBU, BPC, MSF, and ALS162 continue to serve this function.

Longwave also supports maritime and aeronautical navigation via non-directional beacons, and military submarine communication on frequencies below 50 kHz. The band's legacy includes the last operational Alexanderson alternator at SAQ, a World Heritage Site.

However, longwave broadcasting has declined sharply: the BBC's closure of Radio 4 on 198 kHz in 2026 marked the end of a major service, and the radio teleswitch service for electricity meters, broadcast with the longwave signal, was scheduled to end in 2025. The band remains of interest to DXers and amateur radio operators, who use allocations at 135.7–137.8 kHz and the 630 m band (472–479 kHz). The Longwave Club of America focuses on frequencies below 520 kHz.

Did You Know?

• The BBC Radio 4 longwave service on 198 kHz ceased broadcasting at 0000 GMT on 27 June 2026.