A century-old Swedish radio station still broadcasts using a massive, spinning electromechanical machine.

Countries & Cities · Published 29 September 2026 Swipe more like this →

In short: Built in the 1920s to bridge the Atlantic, the Grimeton Radio Station remains the world's only operational Alexanderson alternator. This pre-electronic marvel uses a massive rotating steel disc to generate radio waves. Today, it still fires up annually to send Morse code signals across Europe, preserving a vanished era of communication.

In the early 1920s, nations feared isolation if enemy forces severed their underwater telegraph cables. To secure a direct link to North America, the Swedish Parliament commissioned a high-power radiotelegraphy station. Completed in 1924, Grimeton was equipped with two 200 kW Alexanderson alternators—electromechanical generators that produced radio frequency current through the rapid rotation of a 1.6-meter steel disc. This technology, invented by Ernst Alexanderson, allowed Sweden to handle 95% of its telegram traffic to the United States.

The station’s design was a response to the physics of long-distance transmission. To reach across the Atlantic, it operated in the very low frequency (VLF) range at 17.2 kHz, requiring a massive antenna array. The original system featured six 127-meter-tall steel towers supporting twelve wires spanning over two kilometers. Because the antenna was physically short compared to the 17,440-meter wavelength, engineers used a multiple-tuned design to improve efficiency by an order of magnitude. This setup allowed the station to function as a vital gateway during World War II, when other communication links were frequently cut.

While vacuum tube technology rendered the Alexanderson alternator obsolete shortly after its installation, the station’s sheer scale and capital cost kept it in service for decades. It transitioned into a naval transmitter for submarine communication before eventually being decommissioned from commercial use. Today, the site is a UNESCO World Heritage monument, managed by a foundation that maintains the original machinery. On special occasions like Alexanderson Day, volunteers start the motor, and the station transmits test signals that can be received across the continent, serving as a living museum of industrial history.

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