Shortwave radio is radio transmission using radio frequencies in the shortwave bands (SW). There is no official definition of the band range, but it always includes all of the high frequency band (HF), which extends from 3 to 30 MHz ; above the medium frequency band (MF), to the bottom of the VHF band.
International broadcasting consists of radio and television transmissions that purposefully cross international boundaries, often with then intent of allowing expatriates to remain in touch with their countries of origin as well as educate, inform, and influence residents of foreign countries. Content can range from overt propaganda and counterpropaganda to cultural content to news reports that reflect the point of view and concerns of the originating country or that seek to provide alternative information to that otherwise available as well as promote tourism and trade. In the first half of the twentieth century, international broadcasting was used by colonial empires as a means of connecting colonies with the metropole. When operated by governments or entities close to a government, international broadcasting can be a form of soft power. Less frequently, international broadcasting has been undertaken for commercial purposes by private broadcasters.
High frequency (HF) is the ITU designation for the band of radio waves with frequency between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters. Frequencies immediately below HF are denoted medium frequency (MF), while the next band of higher frequencies is known as the very high frequency (VHF) band. The HF band is a major part of the shortwave band of frequencies, so communication at these frequencies is often called shortwave radio. Because radio waves in this band can be reflected back to Earth by the ionosphere layer in the atmosphere – a method known as "skip" or "skywave" propagation – these frequencies can be used for long-distance communication across intercontinental distances and for mountainous terrains which prevent line-of-sight communications. The band is used by international shortwave broadcasting stations (3.95–25.82 MHz), aviation communication, government time stations, weather stations, amateur radio and citizens band services, among other uses.
In-band on-channel (IBOC) is a hybrid method of transmitting digital radio and analog radio broadcast signals simultaneously on the same frequency. The name refers to the new digital signals being broadcast in the same AM or FM band (in-band), and associated with an existing radio channel (on-channel). By utilizing additional digital subcarriers or sidebands, digital information is multiplexed on existing signals, thus avoiding re-allocation of the broadcast bands.
Digital Radio Mondiale is a set of digital audio broadcasting technologies designed to work over the bands currently used for analogue radio broadcasting including AM broadcasting—particularly shortwave—and FM broadcasting. DRM is more spectrally efficient than AM and FM, allowing more stations, at higher quality, into a given amount of bandwidth, using xHE-AAC audio coding format. Various other MPEG-4 codecs and Opus are also compatible, but the standard now specifies xHE-AAC.
In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature of the Earth, skywave propagation can be used to communicate beyond the horizon, at intercontinental distances. It is mostly used in the shortwave frequency bands.
Marine VHF radio is a worldwide system of two way radio transceivers on ships and watercraft used for bidirectional voice communication from ship-to-ship, ship-to-shore, and in certain circumstances ship-to-aircraft. It uses FM channels in the very high frequency (VHF) radio band in the frequency range between 156 and 174 MHz, designated by the International Telecommunication Union as the VHF maritime mobile band. In some countries additional channels are used, such as the L and F channels for leisure and fishing vessels in the Nordic countries. Transmitter power is limited to 25 watts, giving them a range of about 100 kilometres.
The Sutton Coldfield transmitting station is a broadcasting and telecommunications facility located in Sutton Coldfield, Birmingham, England. In terms of population covered, it is the third most important transmitter in the UK, after Crystal Palace in London and Winter Hill near Bolton.
The Skelton Transmitting Station is a radio transmitter site at grid reference NY433376 near Skelton, Cumbria, England, about 5 miles (8 km) north-west of Penrith, run by Babcock International and owned by the Ministry of Defence. Since the Belmont Mast in Lincolnshire was shortened in 2010, the mast at Skelton has been the tallest structure in the United Kingdom.
Vatican Radio is the official broadcasting service of Vatican City.
The Orfordness transmitting station was a major radio broadcasting facility at Orford Ness on the Suffolk coast in the United Kingdom able to broadcast to much of Europe. It closed in May 2012 after more than 30 years of service. In 2017 Radio Caroline started broadcasting from the site, though not with the same intended coverage of an audience in Europe as the original station.
The Croydon transmitting station is a broadcasting and telecommunications facility on Beaulieu Heights in Upper Norwood, London, England, in the London Borough of Croydon, owned by Arqiva. It was established in 1955 and initially used a small lattice tower. The present tower is 152 metres (499 ft) high and was built in 1962.
The Oxford transmitting station is a broadcasting and telecommunications facility, situated on land 129.5 metres (425 ft) above Ordnance Datum to the north east of the city of Oxford, in Oxfordshire, England. It has a guyed steel lattice mast which is 154.4 metres (507 ft) in height to the top of the main steel structure. The UHF television antenna, which consist of a vertical array of transmitting panels, is mounted above the steel structure. The total height of the mast to the top of this UHF antenna is 165.7 metres (544 ft). It is owned and operated by Arqiva.
Shortwave relay stations are transmitter sites used by international broadcasters to extend their coverage to areas that cannot be reached easily from their home state. For example, the BBC operates an extensive net of relay stations.
CKCX was the call sign used for the Canadian Broadcasting Corporation's shortwave transmitter complex near Sackville, New Brunswick at the Tantramar Marshes. The Sackville Relay Station was operated by Radio Canada International and broadcast its programming around the world as well as relay transmissions from several foreign shortwave broadcasters. Domestically, it transmitted broadcasts on 9.625 MHz to northern Quebec by CBC North, the James Bay Cree Communications Society and Taqramiut Nipingat, the Inuit communications society of the Nunavik region of northern Quebec. The CKCX designation was assigned after CBC Radio's CBA, under whose licence the Sackville complex originally operated, moved to Moncton in 1968. Sackville was also used by Radio Japan, China Radio International, Voice of Vietnam, BBC World Service, Deutsche Welle and Radio Korea as part of a transmitter time exchange agreement.
Curtain arrays are a class of large multielement directional radio transmitting wire antennas, used in the short-wave radio bands. They constitute a type of reflective array antenna, consisting of multiple wire dipole antennas, suspended in a vertical plane, often positioned in front of a "curtain" reflector made of a flat vertical screen of many long parallel wires. These are suspended by support wires strung between pairs of tall steel towers, reaching heights of up to 90 m high. Primarily employed for long-distance skywave transmission, they emit a beam of radio waves at a shallow angle into the sky just above the horizon, which is then reflected by the ionosphere back to Earth beyond the horizon. Curtain arrays are extensively used by international short-wave radio stations for broadcasting to large areas at transcontinental distances.
The Leicester Peak transmitting station is a broadcast transmitting station and communications relay station located near Freetown, Sierra Leone. The site is owned by the Sierra Leone Broadcasting Corporation the country's state broadcaster. It is now the primary transmitting station providing broadcast services for the Western Area of Sierra Leone. Previously the SLBC operated a shortwave transmitting station in Waterloo and a shortwave/mediumwave station in Goderich.
The Wertachtal transmitter site in Bavaria, Germany, was from 1972 to 2013 the biggest shortwave broadcasting facility in Europe. It was located in the valley of the Wertach River near the village of Amberg (Swabia), and was originally operated by Deutsche Bundespost, and later by Media Broadcast GmbH. Before the site was closed, it included 14 500 kW radio transmitters and two 100 kW radio transmitters. It was built in 1969 and demolished in 2014.
Between 1946 and 2023, the BBC Far Eastern Relay Station broadcast BBC World Service radio programmes to large parts of Asia on shortwave and longwave. Transmitting from a number of different sites, notably Tebrau in Malaysia (1953-1979) and then Kranji in Singapore (1979-2023), the station was one of a number of BBC "relay" stations around the world - so named because they "relayed" programmes primarily generated in London - which also included Cyprus, Hong Kong and Oman. The station played a key role in bringing the BBC's impartial news to millions of Asian listeners in the post-war period, when the Cold War was at its height.
