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76-792: ALLISS is a special design case of HRS type antennas . True ALLISS systems have solid radiators (horizontal radiating elements) versus tensioned flexible (open) radiators found with all other variations of ITU HRS type antennas systems. The name is based on a concatenation of two French towns ALLouis and ISSoudun . There are some factors that separate true ALLISS technology from 'run-of-the-mill' rotatable HRS Type antennas. Thales pseudo-ALLISS rotatable antenna designs were procured from other antenna manufacturers that Thales acquired by corporate transactions. Technically only solid radiators distinguish true ALLISS systems from all other rotatable HRS type antennas. Only about 12% (estimate) of all HRS antennas in use globally are rotatable, and of these only 28 of

152-410: A rock music context. In 1975, German electronic music band Kraftwerk recorded a full length concept album around simulated radiowave and shortwave sounds, entitled Radio-Activity . The The 's Radio Cineola monthly broadcasts drew heavily on shortwave radio sound. The development of direct broadcasts from satellites has reduced the demand for shortwave receiver hardware, but there are still

228-466: A "reflector" consisting of many parallel wires in the same orientation as the dipoles. If this was not present, the curtain would radiate equally forward and backward. If there is an "S" in the antenna's designation, it is a steerable design. Following the ITU-recommendation, it might be called 'slewable design'. This might be achieved electronically by adjustment of the electrical wave phases of

304-399: A bandwidth of up to 2:1, allowing them to cover several shortwave bands. Rather than feeding each dipole at its center, which requires a "tree" transmission line structure with complicated impedance matching , multiple dipoles are often connected in series to make an elaborate folded dipole structure which can be fed at a single point. In order to allow the beam to be steered, sometimes

380-678: 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. Due to their powerful directional characteristics, curtain arrays are frequently utilized by government propaganda radio stations to beam propaganda broadcasts across national borders into other nations. For instance, curtain arrays were used by Radio Free Europe and Radio Liberty to broadcast into Eastern Europe . Curtain arrays were originally developed during

456-410: A broadcaster to redirect the entire shortwave transmission network to a strategically important target area in as little as 15 minutes. Modular construction: ALLISS relay stations can be built on a module by module basis. An ALLISS module can start broadcasting as soon as construction is completed. Higher RFI & EMF (electromagnetic) compatibility vs traditional relay stations Each ALLISS module

532-579: 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 (300 feet) high. Primarily employed for long-distance skywave (or skip ) transmission, they emit

608-436: A constant phase shift between adjacent horizontal dipoles allows the direction of the beam to be slewed in azimuth up to ±30° without losing its radiation pattern. Transmission system are optimized for geopolitical reasons. Geopolitical necessity leads some international broadcasters to occasionally use three separate antenna arrays: highband and midband, as well as lowband HRS curtains. Using three curtain arrays to cover

684-458: A given target area. In the early 1920s, Guglielmo Marconi , pioneer of radio, commissioned his assistant Charles Samuel Franklin to carry out a large scale study into the transmission characteristics of short wavelength radio waves and to determine their suitability for long-distance transmissions. Franklin invented the first curtain array aerial system in 1924, known as the 'Franklin' or 'English' system. Other early curtain arrays included

760-403: A great number of shortwave broadcasters. A new digital radio technology, Digital Radio Mondiale (DRM), is expected to improve the quality of shortwave audio from very poor to adequate. The future of shortwave radio is threatened by the rise of power line communication (PLC), also known as Broadband over Power Lines (BPL), which uses a data stream transmitted over unshielded power lines. As

836-421: A large-scale study into the transmission characteristics of short-wavelength waves and to determine their suitability for long-distance transmissions. Franklin rigged up a large antenna at Poldhu Wireless Station , Cornwall , running on 25 kW of power. In June and July 1923, wireless transmissions were completed during nights on 97 meters (about 3 MHz) from Poldhu to Marconi's yacht Elettra in

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912-462: A plane 1 ⁄ 4   wavelength in front of the reflector plane. The reflector wires are oriented parallel to the dipoles. The dipoles may be vertical, radiating in vertical polarization , but are most often horizontal, because horizontally polarized waves are less absorbed by earth reflections. The lowest row of dipoles are mounted more than 1 ⁄ 2  wavelength above the ground, to prevent ground reflections from interfering with

988-417: A result of the multi-layer structure of the ionosphere , propagation often simultaneously occurs on different paths, scattered by the ‘E’ or ‘F’ layer and with different numbers of hops, a phenomenon that may be disturbed for certain techniques. Particularly for lower frequencies of the shortwave band, absorption of radio frequency energy in the lowest ionospheric layer, the ‘D’ layer , may impose

1064-436: A serious limit. This is due to collisions of electrons with neutral molecules, absorbing some of a radio frequency 's energy and converting it to heat. Predictions of skywave propagation depend on: Several different types of modulation are used to incorporate information in a short-wave signal. Amplitude modulation is the simplest type and the most commonly used for shortwave broadcasting . The instantaneous amplitude of

1140-531: A shortwave carrier. These generally require special equipment to decode, such as software on a computer equipped with a sound card. Note that on modern computer-driven systems, digital modes are typically sent by coupling a computer's sound output to the SSB input of a radio. Some established users of the shortwave radio bands may include: Sporadic or non-traditional users of the shortwave bands may include: The World Radiocommunication Conference (WRC), organized under

1216-405: A single transmitter, making it difficult for government authorities to censor them. Shortwave radio is also often used by aircraft. The name "shortwave" originated during the beginning of radio in the early 20th century, when the radio spectrum was divided into long wave (LW), medium wave (MW), and short wave (SW) bands based on the length of the wave. Shortwave radio received its name because

1292-459: A standardised nomenclature for describing curtain antennas, CCIR HF Transmitting Antennas consisting of 1 to 4 letters followed by three numbers: For example, a "HRS 4/5/0.5" curtain antenna has a rectangular array of 20 dipoles, 4 dipoles wide and 5 dipoles high, with the lowest row being half a wavelength off the ground, and a flat reflector behind it, and the direction of the beam can be slewed. An HRS 4/4/0.5 slewable antenna with 16 dipoles

1368-532: A very limited spectrum available for long-distance communication, and the very expensive transmitters , receivers and gigantic antennas. Long waves are also difficult to beam directionally, resulting in a major loss of power over long distances. Prior to the 1920s, the 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 , pioneer of radio, commissioned his assistant Charles Samuel Franklin to carry out

1444-457: Is an incomplete list of stations using only HRS antennas, sorted by country name. Brazil Germany New Zealand UK Australia Germany Canada Spain USA Some portable tactical antenna systems still use HR type antennas, mostly not HRS as the antennas are rotatable. ALLISS Technology portals Shortwave Shortwave radio is radio transmission using radio frequencies in

1520-504: Is at Issoudun/Ste Aoustrille. Issoudun is currently utilized by TDF for shortwave transmissions. The site uses 12 rotary ALLISS antennas fed by 12 transmitters of 500 kW each to transmit shortwave broadcasts by Radio France International (RFI), along with other broadcast services. Applicable related technologies Broadcasters using ALLISS modules ALLISS Shortwave Broadcasting & ALLISS Technology Portal (Internet Archive) HRS type antennas Curtain arrays are

1596-400: Is customarily used below 10 MHz and USB (upper sideband) above 10 MHz, non-amateur services use USB regardless of frequency. Vestigial sideband transmits the carrier and one complete sideband, but filters out most of the other sideband. It is a compromise between AM and SSB, enabling simple receivers to be used, but requires almost as much transmitter power as AM. Its main advantage

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1672-455: Is eliminated as well as the residual carrier, only the remaining set is transmitted. This reduces power in the transmission, as roughly 2 ⁄ 3 of the energy sent by an AM signal is in the carrier, which is not needed to recover the information contained in the signal. It also reduces signal bandwidth , enabling less than one-half the AM signal bandwidth to be used. The drawback is the receiver

1748-476: Is for transmitting audio, like the analog modes above. Continuous wave (CW) is on-and-off keying of a sine-wave carrier, used for Morse code communications and Hellschreiber facsimile -based teleprinter transmissions. It is a data mode, although often listed separately. It is typically received via lower or upper SSB modes. Radioteletype , fax, digital, slow-scan television , and other systems use forms of frequency-shift keying or audio subcarriers on

1824-614: Is fully automated, so there is no need for technical staff. When there are 2-5 ALLISS modules scattered over several hundred square kilometers, a three-person support staff is enough to keep the modules in operation year round (provided these modules are visited monthly for repair and maintenance). With conventionally designed HRS type antennas shortwave relay stations and their obligatory transmitter hall, switch matrix, coaxial or open feeder line systems and multiple antennas (~90% of shortwave relay stations are built this way) much larger staffs are required. Around US$ 10 million. According to

1900-417: Is more complicated, since it must re-create the carrier to recover the signal. Small errors in the detection process greatly affect the pitch of the received signal. As a result, single sideband is not used for music or general broadcast. Single sideband is used for long-range voice communications by ships and aircraft, citizen's band , and amateur radio operators. In amateur radio operation lower sideband (LSB)

1976-529: Is necessary. ALLISS is only used by well funded broadcasting and telecommunications operations that intend to use the modules over their design lifespan of 50–60 years. ALLISS allows a broadcaster to change the following shortwave transmission parameters at any time: direction ( azimuths from 0 to 360 degrees, rate: ~1 deg / 6 sec), broadcast frequency , and antenna configuration (i.e.: HR 4/4/1 -> HR 6/4/1). All of these transmission mode changes can take effect in as little as 5 minutes. This flexibility can allow

2052-542: Is not available for use in the 26 MHz band. One Low Band antenna exists for Tropical Band broadcasting. It takes up the entire back side of the ALLISS module. This Low Band antenna counterbalances the primary transmission antennas used in traditional shortwave broadcasting. Documentation format — Nation : Broadcaster : City (Modules, Date Sold) Total number of modules sold since 1989: 32 The International broadcasting center of TDF (Télédiffusion de France)

2128-410: Is one of the standard types of array seen at shortwave broadcast stations worldwide. The HRS type antenna is one of the most common types of curtain array. The name comes from the above CCIR nomenclature: it consists of an array of H orizontal dipoles with a R eflector behind them, and the beam is S teerable. These antennas are also known as "HRRS" (for a R eversible R eflector), but the extra R

2204-448: Is seldom used. However, as far back as the mid-1930s, Radio Netherlands was using a rotatable HRS antenna for global coverage. Since the 1950s the HRS design has become more or less the standard for long distance (> 1000 km) high power shortwave broadcasting. An HRS type antenna is basically a rectangular array of conventional dipole antennas strung between supporting towers. In

2280-537: Is that only half the bandwidth of an AM signal is used. It is used by the Canadian standard time signal station CHU . Vestigial sideband was used for analog television and by ATSC , the digital TV system used in North America. Narrow-band frequency modulation (NBFM or NFM) is used typically above 20 MHz. Because of the larger bandwidth required, NBFM is commonly used for VHF communication. Regulations limit

2356-587: The ALLISS antenna technology) to concentrate radio energy at the target area. Shortwave possesses a number of advantages over newer technologies: Shortwave radio's benefits are sometimes regarded as being outweighed by its drawbacks, including: The Asia-Pacific Telecommunity estimates that there are approximately 600 million shortwave broadcast-radio receivers in use in 2002. WWCR claims that there are 1.5 billion shortwave receivers worldwide. Many hobbyists listen to shortwave broadcasters. In some cases,

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2432-506: The Cape Verde Islands . In September 1924, Marconi arranged for transmissions to be made day and night on 32 meters (about 9.4 MHz) from Poldhu to his yacht in the harbour at Beirut , to which he had sailed, and was "astonished" to find he could receive signals "throughout the day". Franklin went on to refine the directional transmission by inventing the curtain array aerial system. In July 1924, Marconi entered into contracts with

2508-479: 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 (100 (exactly 99.930819333) to 10 (exactly 9.9930819333) meters); above the medium frequency band (MF) , to the bottom of the VHF band . Radio waves in the shortwave band can be reflected or refracted from a layer of electrically charged atoms in

2584-414: The 1920s and 1930s when there was a lot of experimentation with long distance shortwave broadcasting. The underlying concept was to achieve improvements in gain and/or directionality over the simple dipole antenna , possibly by folding one or more dipoles into a smaller physical space, or to arrange multiple dipoles such that their radiation patterns reinforce each other, thus concentrating more signal into

2660-416: The 1920s. 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, some commercial longwave communications stations remained in use until

2736-700: The 1930s and 1940s. The Sterba curtain is however a narrowband design and is only steerable by mechanical means. Curtain arrays were used in some of the first radar systems, such as Britain's Chain Home network. During the Cold War , large curtain arrays were used by the Voice of America , Radio Free Europe , and Radio Liberty , and analogous Western European organizations, to beam propaganda broadcasts into communist countries, which censored Western media. The driven elements are usually half-wave dipoles , fed in phase, mounted in

2812-421: The 1960s. Long-distance radio circuits also reduced the need for new cables, although the cables maintained their advantages of high security and a much more reliable and better-quality signal than shortwave. The cable companies began to lose large sums of money in 1927. A serious financial crisis threatened viability of cable companies that were vital to strategic British interests. The British government convened

2888-510: The 2005 Thales brochure on ALLISS there are 6 different versions of the ALLISS system. These versions are sorted by date of initial installation. Typically ALLISS modules possess a 500 kW polyphase shortwave transmitter. Three HRS array antennas types are available for broadcasting in the traditional shortwave broadcasting bands. For tropical and lower frequency shortwave broadcasting For traditional shortwave broadcasting For highly directional shortwave broadcasting The HRS 6/4/1

2964-501: The ALLISS systems have solid radiators. One must assume that only about 10% of HRS type antennas are rotatable, but compiled statistics are fragmentary. Only about 20% of rotatable HRS antennas are ALLISS, but this may be a slight overestimate. The Transmitter Documentation Project has most but not all stats on shortwave relay station antennas in use or historical. The Chinese SARFT is said to contain replicated ALLISS module technology, so to consider ALLISS technology as being exclusively in

3040-522: The BPL frequencies used overlap with shortwave bands, severe distortions can make listening to analog shortwave radio signals near power lines difficult or impossible. According to Andy Sennitt, former editor of the World Radio TV Handbook , shortwave is a legacy technology, which is expensive and environmentally unfriendly. A few countries are hanging on to it, but most have faced up to the fact that

3116-522: The Beethoven Bicentennial in Opus ;1970 with filtered and distorted snippets of Beethoven pieces – Spiral (1968), Pole , Expo (both 1969–1970), and Michaelion (1997). Cypriot composer Yannis Kyriakides incorporated shortwave numbers station transmissions in his 1999 ConSPIracy cantata . Holger Czukay , a student of Stockhausen, was one of the first to use shortwave in

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3192-641: The British General Post Office (GPO) 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. Beam Wireless Services from the UK to Australia, South Africa and India went into service in 1927. Shortwave communications began to grow rapidly in

3268-514: The Bruce array patented by Edmond Bruce in 1927, and the Sterba curtain , patented by Ernest J. Sterba in 1929. The Bruce array produces a vertically polarised signal; Sterba arrays (and the later HRS antennas) produce a horizontally-polarised signal. The first curtain array to achieve popularity was the Sterba curtain , patented by Ernest J. Sterba in 1929 and this was used by Bell Labs and others during

3344-511: The HF broadcasting spectrum creates a highly optimized HF transmission system, but three or more curtain arrays can be costly to build and maintain, and no new HF relay stations have been built since the mid-1990s. The modern HRS antenna design has a long lifespan, however, so existing HRS shortwave transmission systems built before 1992 will likely remain available for some time. Since 1984 the CCIR has created

3420-575: The Imperial Wireless and Cable Conference in 1928 "to examine the situation that had arisen as a result of the competition of Beam Wireless with the Cable Services". It recommended and received government approval for all overseas cable and wireless resources of the Empire to be merged into one system controlled by a newly formed company in 1929, Imperial and International Communications Ltd. The name of

3496-601: The Internet, in that they listen only, and never attempt to send out their own signals. Other listeners participate in clubs, or actively send and receive QSL cards, or become involved with amateur radio and start transmitting on their own. Many listeners tune the shortwave bands for the programmes of stations broadcasting to a general audience (such as Radio Taiwan International , China Radio International , Voice of America , Radio France Internationale , BBC World Service , Voice of Korea , Radio Free Sarawak etc.). Today, through

3572-521: The Second National Radio Conference in 1923 – forced amateurs to shift to shorter and shorter wavelengths; however, amateurs were limited by regulation to wavelengths longer than 150 meters (2 MHz). A few fortunate amateurs who obtained special permission for experimental communications at wavelengths shorter than 150 meters completed hundreds of long-distance two-way contacts on 100 meters (3 MHz) in 1923 including

3648-452: The assigned bands, there may be small differences between countries or regions. For example, in the official bandplan of the Netherlands , the 49 m band starts at 5.95 MHz, the 41 m band ends at 7.45 MHz, the 11 m band starts at 25.67 MHz, and the 120 m, 90 m, and 60 m bands are absent altogether. International broadcasters sometimes operate outside

3724-474: The atmosphere called the Ionosphere . Therefore, short waves directed at an angle into the sky can be reflected back to Earth at great distances, beyond the horizon. This is called skywave or "skip" propagation . Thus shortwave radio can be used for communication over very long distances, in contrast to radio waves of higher frequency, which travel in straight lines ( line-of-sight propagation ) and are limited by

3800-486: The auspices of the International Telecommunication Union , allocates bands for various services in conferences every few years. The last WRC took place in 2023. As of WRC-97 in 1997, these bands were allocated for international broadcasting . AM shortwave broadcasting channels are allocated with a 5 kHz separation for traditional analog audio broadcasting: Although countries generally follow

3876-451: The bandwidth of a signal transmitted in the HF bands, and the advantages of frequency modulation are greatest if the FM signal has a wide bandwidth. NBFM is limited to short-range transmissions due to the multiphasic distortions created by the ionosphere. Digital Radio Mondiale (DRM) is a digital modulation for use on bands below 30 MHz. It is a digital signal, like the data modes, below, but

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3952-431: The carrier is controlled by the amplitude of the signal (speech, or music, for example). At the receiver, a simple detector recovers the desired modulation signal from the carrier. Single-sideband transmission is a form of amplitude modulation but in effect filters the result of modulation. An amplitude-modulated signal has frequency components both above and below the carrier frequency . If one set of these components

4028-457: The circular railway. Another physical rotation technique is employed by the ALLISS system where the entire array is built around a central rotatable tower of great strength. Electrically slewed antenna arrays can usually be aimed in the range of ±30° from the antenna's physical direction while mechanically rotated arrays can accommodate a full 360°. Electrical slewing is typically done in the horizontal plane, with some adjustment being possible in

4104-586: The company was changed to Cable and Wireless Ltd. in 1934. A resurgence of long-distance cables began in 1956 with the laying of TAT-1 across the Atlantic Ocean, the first voice frequency cable on this route. This provided 36 high-quality telephone channels and was soon followed by even higher-capacity cables all around the world. Competition from these cables soon ended the economic viability of shortwave radio for commercial communication. Amateur radio operators also discovered that long-distance communication

4180-549: The distribution of radio programs, such as satellite radio and cable broadcasting as well as IP-based transmissions , shortwave broadcasting lost importance. Initiatives for the digitization of broadcasting did not bear fruit either, and so as of 2024 , few broadcasters continue to broadcast programs on shortwave. However, shortwave remains important in war zones, such as in the Russo-Ukrainian war , and shortwave broadcasts can be transmitted over thousands of miles from

4256-420: The domain of Thales is no longer true. Information about ALLISS can also be found associated with Ampegon , Thales Group , Thomson-CSF . ALLISS technology, due to its cost and complexity—is out of reach to most consumers as a consumer product. Cheaper solutions to ALLISS exist in the shortwave broadcasting technology area. As a rule of thumb ALLISS systems should only be purchased if 360 degrees of coverage

4332-507: The entire array is suspended by cantilever arms from a single large tower which can be rotated. See ALLISS-Antenna . Alternatively, some modern versions are constructed as phased arrays in which the beam can be slewed electronically, without moving the antenna. Each dipole or group of dipoles is fed through an electronically adjustable phase shifter , implemented either by passive networks of capacitors and inductors which can be switched in and out, or by separate output RF amplifiers . Adding

4408-572: The evolution of the Internet, the hobbyist can listen to shortwave signals via remotely controlled or web controlled shortwave receivers around the world, even without owning a shortwave radio. Many international broadcasters offer live streaming audio on their websites and a number have closed their shortwave service entirely, or severely curtailed it, in favour of internet transmission. Shortwave listeners, or SWLs, can obtain QSL cards from broadcasters, utility stations or amateur radio operators as trophies of

4484-713: The first successful transatlantic tests in December ;1921, operating in the 200 meter mediumwave band (near 1,500 kHz, inside the modern AM broadcast band), which at that time was the shortest wavelength / highest frequency available to amateur radio. In 1922 hundreds of North American amateurs were heard in Europe on 200 meters and at least 20 North American amateurs heard amateur signals from Europe. The first two-way communications between North American and Hawaiian amateurs began in 1922 at 200 meters. Although operation on wavelengths shorter than 200 meters

4560-597: The first transatlantic two-way contacts. By 1924 many additional specially licensed amateurs were routinely making transoceanic contacts at distances of 6,000 miles (9,600 km) and more. On 21 September 1924 several amateurs in California completed two-way contacts with an amateur in New Zealand . On 19 October amateurs in New Zealand and England completed a 90 minute two-way contact nearly halfway around

4636-472: The goal is to hear as many stations from as many countries as possible ( DXing ) ; others listen to specialized shortwave utility, or "ute", transmissions such as maritime, naval, aviation, or military signals. Others focus on intelligence signals from numbers stations , stations which transmit strange broadcast usually for intelligence operations, or the two way communications by amateur radio operators. Some short wave listeners behave analogously to "lurkers" on

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4712-492: The harmonics of natural sound and creating at times a strange "spacey" quality due to echoes and phase distortion. Evocations of shortwave reception distortions have been incorporated into rock and classical compositions, by means of delays or feedback loops, equalizers, or even playing shortwave radios as live instruments. Snippets of broadcasts have been mixed into electronic sound collages and live musical instruments, by means of analogue tape loops or digital samples . Sometimes

4788-573: The hobby. Some stations even give out special certificates, pennants, stickers and other tokens and promotional materials to shortwave listeners. Some musicians have been attracted to the unique aural characteristics of shortwave radio which – due to the nature of amplitude modulation, varying propagation conditions, and the presence of interference – generally has lower fidelity than local broadcasts (particularly via FM stations). Shortwave transmissions often have bursts of distortion, and "hollow" sounding loss of clarity at certain aural frequencies, altering

4864-809: The normal the WRC-allocated bands or use off-channel frequencies. This is done for practical reasons, or to attract attention in crowded bands (60 m, 49 m, 40 m, 41 m, 31 m, 25 m). The new digital audio broadcasting format for shortwave DRM operates 10 kHz or 20 kHz channels. There are some ongoing discussions with respect to specific band allocation for DRM, as it mainly transmitted in 10 kHz format. The power used by shortwave transmitters ranges from less than one watt for some experimental and amateur radio transmissions to 500 kilowatts and higher for intercontinental broadcasters and over-the-horizon radar . Shortwave transmitting centers often use specialized antenna designs (like

4940-405: The radiation pattern. This allows most of the radiation to be concentrated in a narrow main lobe aimed a few degrees above the horizon, which is ideal for skywave transmission. A curtain array may have a gain of 20  dB greater than a simple dipole antenna. Because of the strict phase requirements, earlier curtain arrays had a narrow bandwidth, but modern curtain arrays can be built with

5016-415: The signals fed to the columns of dipole antenna elements, or physically by mounting the antenna array on a large rotating mechanism. An example of this can be seen at NRK Kvitsøy, where a circular railway carries a pair of wheeled platforms, each of which supports a tower at opposite ends of a diameter-arm. The curtain antenna array is suspended between the towers and rotates with them as the towers go around

5092-437: The simplest case, each dipole is separated from the next by 1 ⁄ 2   λ vertically, and the centres of each dipole are spaced 1  λ apart horizontally. Again, in the simplest case (for a broadside beam), all dipoles are driven in phase with each other and with equal power. Radiation is concentrated broadside to the curtain. Behind the array of dipoles, typically about 1 ⁄ 3   λ away there will be

5168-505: The sounds of instruments and existing musical recordings are altered by remixing or equalizing, with various distortions added, to replicate the garbled effects of shortwave radio reception. The first attempts by serious composers to incorporate radio effects into music may be those of the Russian physicist and musician Léon Theremin , who perfected a form of radio oscillator as a musical instrument in 1928 ( regenerative circuits in radios of

5244-473: The time were prone to breaking into oscillation , adding various tonal harmonics to music and speech); and in the same year, the development of a French instrument called the Ondes Martenot by its inventor Maurice Martenot , a French cellist and former wireless telegrapher. Karlheinz Stockhausen used shortwave radio and effects in works including Hymnen (1966–1967), Kurzwellen (1968) – adapted for

5320-482: The vertical plane. The number of dipole rows and the height of the lowest element above ground determine the elevation angle and consequently the distance to the service area. Note that it is possible for details of the antenna site to wreak havoc with the designers plans such that takeoff angle and matching may be adversely affected. This is an example of theoretical HRS design shortwave relay stations. This may help one better understand HRS antenna directivity. This

5396-399: The visual horizon, about 64 km (40 miles). Shortwave broadcasts of radio programs played an important role in the early days of radio history. In World War II it was used as a propaganda tool for an international audience. The heyday of international shortwave broadcasting was during the Cold War between 1960 and 1980. With the wide implementation of other technologies for

5472-414: The wavelengths in this band are shorter than 200 m (1,500 kHz) which marked the original upper limit of the medium frequency band first used for radio communications. The broadcast medium wave band now extends above the 200 m / 1,500 kHz limit. Early long-distance radio telegraphy used long waves, below 300  kilohertz (kHz) / above 1000 m. The drawbacks to this system included

5548-603: The world. On 10 October the Third National Radio Conference made three shortwave bands available to U.S. amateurs at 80 meters (3.75 MHz), 40 meters (7 MHz) and 20 meters (14 MHz). These were allocated worldwide, while the 10 meter band (28 MHz) was created by the Washington International Radiotelegraph Conference on 25 November 1927. The 15 meter band (21 MHz)

5624-596: Was opened to amateurs in the United States on 1 May 1952. Shortwave radio frequency energy is capable of reaching any location on the Earth as it is influenced by ionospheric reflection back to Earth by the ionosphere , (a phenomenon known as " skywave propagation"). A typical phenomenon of shortwave propagation is the occurrence of a skip zone where reception fails. With a fixed working frequency, large changes in ionospheric conditions may create skip zones at night. As

5700-472: Was possible on shortwave bands. Early long-distance services used surface wave propagation at very low frequencies , which are attenuated along the path at wavelengths shorter than 1,000 meters. Longer distances and higher frequencies using this method meant more signal loss. This, and the difficulties of generating and detecting higher frequencies, made discovery of shortwave propagation difficult for commercial services. Radio amateurs may have conducted

5776-405: Was technically illegal (but tolerated at the time as the authorities mistakenly believed that such frequencies were useless for commercial or military use), amateurs began to experiment with those wavelengths using newly available vacuum tubes shortly after World War I. Extreme interference at the longer edge of the 150–200 meter band – the official wavelengths allocated to amateurs by

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