Shortwave radio
Shortwave radio enables long-distance communication via ionospheric reflection.
Shortwave radio transmits signals using the shortwave bands, a part of the radio spectrum. While there is no strict official definition, these bands always include the high frequency (HF) range, which runs from 3 to 30 MHz (roughly 100 to 10 meters in wavelength). This sits between the medium frequency (MF) band and the lower end of the VHF band. What makes shortwave special is that its radio waves can bounce off or bend through the ionosphere—a layer of electrically charged atoms in the upper atmosphere. By aiming waves upward, they can be reflected back to Earth far beyond the horizon, a phenomenon called skywave or "skip" propagation. This allows shortwave to cover enormous distances, unlike higher-frequency waves that travel in straight lines and are usually limited to the visual horizon, about 64 km (40 miles).
Shortwave radio is used to broadcast voice and music over vast areas, sometimes spanning entire continents or more. Other uses include military over-the-horizon radar, diplomatic communication, two-way international communication by amateur radio enthusiasts (for hobby, education, and emergency services), and long-distance aviation and marine communications. For decades, shortwave broadcasts of radio programs were a major tool in international broadcasting, delivering news and information while also serving as propaganda for global audiences. Newer technologies like satellite radio, cable broadcasting, and Internet radio have largely replaced shortwave for long-distance program distribution. Still, shortwave listening remains a niche hobby, with enthusiasts tuning in to fringe stations.
Shortwave radio is especially valuable in war zones, such as during the Russo-Ukrainian war. A single transmitter can send signals thousands of miles, making it hard for governments to censor. It is also commonly used by aircraft.
**History**
The term "shortwave" dates back to the early 20th century, when the radio spectrum was divided into long wave (LW), medium wave (MW), and short wave (SW) based on wavelength. It got its name because these wavelengths are shorter than 200 meters (1,500 kHz), which was the original upper limit of the medium frequency band used for early radio communications. (The broadcast medium wave band now extends above that limit.)
Early long-distance radio telegraphy relied on long waves below 300 kHz (above 1000 meters).
- Frequency range
- 3 to 30 MHz (HF band)
- Wavelength range
- approximately 100 to 10 metres
- Typical skywave range
- beyond the visual horizon, about 64 km (40 miles) for line-of-sight
- First commercial beam service
- UK to Canada, 25 October 1926
- Early transatlantic amateur contacts
- December 1921 on 200 meters
- First two way transatlantic amateur cont
- 1923 on 100 meters (3 MHz)
Lore & Background
The name 'shortwave' originated during the early 20th century, when the radio spectrum was divided into long wave (LW), medium wave (MW), and short wave (SW) bands based on wavelength. Shortwave received its name because the wavelengths in this band are shorter than 200 m (1,500 kHz), which marked the original upper limit of the medium frequency band. Early long-distance radio telegraphy used long waves below 300 kHz, but these required very expensive transmitters, receivers, and gigantic antennas, and were difficult to beam directionally. Prior to the 1920s, shortwave frequencies above 1.5 MHz were regarded as useless for long-distance communication and were designated in many countries for amateur use.
Guglielmo Marconi commissioned his assistant Charles Samuel Franklin to study short-wavelength transmission characteristics. In June and July 1923, wireless transmissions were completed during nights on 97 meters (about 3 MHz) from Poldhu Wireless Station, Cornwall, to Marconi's yacht Elettra in the Cape Verde Islands. In September 1924, Marconi arranged for transmissions day and night on 32 meters (about 9.4 MHz) from Poldhu to his yacht in Beirut. Franklin refined directional transmission by inventing the curtain array aerial system. In July 1924, Marconi contracted with the British General Post Office to install high-speed shortwave telegraphy circuits from London to Australia, India, South Africa and Canada as the main element of the Imperial Wireless Chain. The UK-to-Canada shortwave 'Beam Wireless Service' went into commercial operation on 25 October 1926, with services to Australia, South Africa and India following in 1927.
Amateur radio operators also discovered long-distance communication on shortwave bands. In December 1921, radio amateurs may have conducted the first successful transatlantic tests operating in the 200 meter mediumwave band. By 1924, many specially licensed amateurs were routinely making transoceanic contacts at distances of 6,000 miles (9,600 km) and more. On 21 September 1924, amateurs in California completed two-way contacts with an amateur in New Zealand, and on 19 October, amateurs in New Zealand and England completed a 90-minute two-way contact nearly halfway around the world.
Reader's Guide
Shortwave radio is used for broadcasting of voice and music to shortwave listeners over very large areas, sometimes entire continents or beyond. Other uses include military over-the-horizon radar, diplomatic communication, amateur radio enthusiasts' two-way international communication for hobby, education, and emergency service, and long-distance aviation and marine communications. Shortwave broadcasts of radio programs played an important role in international broadcasting for many decades, serving both to provide news and information and as a propaganda tool for an international audience. Other technologies have come to replace shortwave for long-distance distribution of radio programs, such as satellite radio, cable broadcasting, and Internet radio. However, shortwave listening remains a niche hobby, with enthusiasts tuning in to fringe stations. Shortwave radio is important in war zones, such as in the Russo-Ukrainian war, and shortwave broadcasts can be transmitted over thousands of miles from a single transmitter, making it difficult for government authorities to censor them. Shortwave radio is also often used by aircraft. By 1928, more than half of long-distance communications had moved from transoceanic cables and longwave wireless services to shortwave, and the overall volume of transoceanic shortwave communications had vastly increased. Shortwave stations had cost and efficiency advantages over massive longwave wireless installations. However, competition from high-capacity submarine cables laid from 1956 onward soon ended the economic viability of shortwave radio for commercial communication.
Did You Know?
- Shortwave radio can be reflected or refracted from the ionosphere, enabling skywave or 'skip' propagation over great distances.
- The first commercial shortwave 'Beam Wireless Service' from the UK to Canada began operation on 25 October 1926.
- In 1923, Marconi's assistant Charles Samuel Franklin conducted night-time transmissions on 97 meters from Cornwall to the Cape Verde Islands.
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