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"Grundig Satellit 400 solid-state, digital "shortwave receiver, circa 1986 [1]

Shortwave radio is "radio transmission using shortwave "radio frequencies. There is no official definition of the band, but the range always includes all of the "high frequency band (HF), and generally extends from 1.7–30 MHz (176.3–10.0 m); from the high end of the "medium frequency band (MF) just above the "mediumwave AM broadcast band, to the end of the "HF band.

Radio waves in the shortwave band can be reflected or refracted from a layer of electrically charged atoms in 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 very long distance communication, in contrast to radio waves of higher frequency which travel in straight lines ("line-of-sight propagation) and are limited by the visual horizon, about 40 miles (64 km). Shortwave radio is used for "broadcasting of voice and music to "shortwave listeners over very large areas; sometimes entire continents or beyond. It is also used for military "over-the-horizon radar, diplomatic communication, and two-way international communication by "amateur radio enthusiasts for hobby, educational and emergency purposes.


Frequency classifications[edit]

The widest popular definition of the shortwave frequency interval is the "ITU Region 1 (EU+Africa+Russia...) definition, and is the span 1.6–30 "MHz, just above the "medium wave band, which ends approximately at 1.6 MHz.

There are also other definitions of the shortwave frequency interval:

The term short wave is an historic one, dating from the early 20th century, when the "radio spectrum was divided on the basis of "wavelength into "longwave (LW), "medium wave (MW), and short wave (SW) radio bands. Shortwave radio 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 "first used for radio communications. The broadcast "medium wave band now extends above the 200 m/1,500 kHz limit, and the "amateur radio 1.8 MHz – 2.0 MHz band (known as the ""top band") is the lowest-frequency band considered to be 'shortwave'.



Radio amateurs carried out the first shortwave transmissions over a long distance before "Guglielmo Marconi

The name "shortwave" originated during the early days of radio in the early 20th century, when the "radio spectrum was considered divided into "long wave (LW), "medium wave (MW) and short wave bands based on the "wavelength of the "radio waves. Early long distance "radio telegraphy used "long waves, below 300 "kilohertz (kHz). The drawbacks to this system included a very limited spectrum available for long distance communication, and the very expensive "transmitters, receivers and gigantic antennas that were required. It was also difficult to beam the radio wave directionally with long wave, 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.[6]

"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 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 from Poldhu to Marconi's yacht Elettra in the "Cape Verde Islands.[7]

In September 1924, Marconi transmitted daytime and nighttime on 32 meters from Poldhu to his yacht in Beirut. Franklin went on to refine the directional transmission, by inventing the "curtain array aerial system.[8][9] In July 1924, Marconi entered into contracts with 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.[7]

Shortwave communications began to grow rapidly in the 1920s,[10] similar to the internet in the late 20th century. 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,[11] however some commercial longwave communications stations remained in use until the 1960s. Long distance radio circuits also reduced the load on the existing transoceanic telegraph cables and hence 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, and a serious financial crisis threatened the viability of cable companies that were vital to strategic British interests. The British government convened the Imperial Wireless and Cable Conference[12] 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 the company was changed to "Cable and Wireless Ltd. in 1934.

Long-distance cables had a resurgence beginning 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. These sounded the death knell of shortwave radio for commercial communications.

Amateur use of shortwave propagation[edit]

"Hallicrafters SX-28 shortwave receiver analog tuning dial, circa 1944

"Amateur radio operators also discovered that long-distance communication was possible on shortwave bands. Early long-distance services used "surface wave propagation at "very low frequencies,[13] 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 the first successful transatlantic tests in December 1921,[14] operating in the 200 meter "mediumwave band (near 1,500 kHz in the modern AM broadcast band) – the shortest wavelength then available to amateurs. 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 was technically illegal (but tolerated as the authorities mistakenly believed at first 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 the Second National Radio Conference[15] 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 the first transatlantic two way contacts.[16]

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 the world. On 10 October the Third National Radio Conference made three shortwave bands available to U.S. amateurs[17] 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[18] on 25 November 1927. The "15 meter band (21 MHz) was opened to amateurs in the United States on 1 May 1952.

Propagation characteristics[edit]

Formation of a "skip zone

Shortwave radio frequency energy is capable of reaching any location on the Earth as it is influenced by "ionospheric reflection back to the 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 a result of the multi-layer structure of the ionosphere, propagation often simultaneously occurs on different paths, "scattered by the E or F region 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 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.[19] Predictions of skywave propagation depend on:

Types of modulation[edit]

National Panasonic R3000 analog shortwave receiver, circa 1965 [20]

Several different types of modulation are used to impress information on a short-wave transmission.

"Amplitude modulation is the simplest type and the most commonly used for shortwave broadcasting. The instantaneous amplitude of 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 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 unnecessary to recover the information contained on it. It also reduces "bandwidth", enabling about one-half the carrier frequency spectrum width to be used. The drawback is the receiver 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. Lower sideband (LSB) is generally used below 9 MHz and USB (upper sideband) above 9 MHz.

"Vestigal sideband transmits the carrier and one complete sideband, but filters out the other sideband. It is a compromise between AM and SSB, enabing simple receivers to be used, but requires almost as much transmitter power as AM. One advantage is only half the bandwidth of an AM signal is used. It can be heard in the transmission of certain radio "time signal stations. "Vestigial sideband is used for over the air Television Broadcasts both analog and "digital.

"Continuous wave (CW) is "on-and-off keying of a carrier, used for "Morse code communications and "Hellschreiber "facsimile-based "teleprinter transmissions.[21]

Narrow-band "frequency modulation (NBFM) is used typically above 20 MHz. Because of the larger "bandwidth required, NBFM is commonly used for "VHF communication. Regulations limit 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.[22]

"Digital Radio Mondiale (DRM) is a digital modulation for use on bands below 30 MHz.

"Radioteletype, fax, digital, "slow-scan television and other systems use forms of frequency-shift keying or audio subcarriers on a shortwave carrier. These generally require special equipment to decode, such as software on a computer equipped with a sound card.


Portable shortwave receiver's digital display tuned to the "75 meter band

Some established users of the shortwave radio bands may include:

Sporadic or non-traditional users of the shortwave bands may include:

Shortwave broadcasting[edit]

See "International broadcasting for details on the history and practice of broadcasting to foreign audiences.

See "Shortwave relay station for the actual kinds of integrated technologies used to bring high power signals to listeners.

Frequency allocations[edit]

The "World Radiocommunication Conference (WRC), organized under the auspices of the "International Telecommunication Union, allocates bands for various services in conferences every few years. The last WRC took place in 2007.

At WRC-97 in 1997, the following bands were allocated for "international broadcasting. AM shortwave broadcasting channels are allocated with a 5 kHz separation for traditional analog audio broadcasting.

Metre Band Frequency Range Remarks
120 m 2.3–2.495 MHz tropical band
90 m 3.2–3.4 MHz tropical band
75 m 3.9–4 MHz shared with the North American "amateur radio 80m band
60 m 4.75–5.06 MHz tropical band
49 m 5.9–6.2 MHz  
41 m 7.2–7.6 MHz shared with the "amateur radio 40m band
31 m 9.4–9.9 MHz currently the most heavily used band
25 m 11.6–12.2 MHz  
22 m 13.57–13.87 MHz
19 m 15.1–15.8 MHz  
16 m 17.48–17.9 MHz  
15 m 18.9–19.02 MHz almost unused, could become a DRM band
13 m 21.45–21.85 MHz  
11 m 25.6–26.1 MHz may be used for local DRM broadcasting

Although countries generally follow the table above, there may be small differences between countries or regions. For example, in the official bandplan of the "Netherlands,[28] 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, 90 and 60 m bands are absent altogether. Additionally, international broadcasters sometimes operate outside the normal WRC-allocated bands or use off-channel frequencies. This is done for practical reasons, or to attract attention in crowded bands (60m, 49m, 40m, 41m, 31m, 25m).

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 the "ALLISS antenna technology) to concentrate radio energy at the target area.


"Soviet shortwave listener in "Borisoglebsk, 1941

Shortwave does possess a number of advantages over newer technologies, including the following:


Shortwave radio's benefits are sometimes regarded as being outweighed by its drawbacks, including:

Shortwave listening[edit]

A pennant sent to overseas listeners by "Radio Budapest in the late 1980s

The Asia-Pacific Telecommunity estimates that there are approximately 600 million "shortwave broadcast-radio receivers in use in 2002.[31] "WWCR claims that there are 1.5 billion shortwave receivers worldwide.[32]

Many hobbyists listen to shortwave broadcasters. In some cases, 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 the Internet, in that they listen only and never make any 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 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.[33] 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 the hobby. Some stations even give out special certificates, pennants, stickers and other tokens and promotional materials to shortwave listeners.

Shortwave broadcasts and music[edit]

Composer "Karlheinz Stockhausen

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 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 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.[34][35][36]

The first attempts by serious composers to incorporate radio effects into music may be those of the Russian physicist and musician "Léon Theremin,[36] who perfected a form of radio oscillator as a musical instrument in 1928 ("regenerative circuits in radios of 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 (1966–67), "Kurzwellen (1968)—adapted for the Beethoven Bicentennial in Opus 1970 with filtered and distorted snippets of Beethoven pieces—"Spiral (1968), "Pole, "Expo (both 1969–70), and "Michaelion (1997).[34]

"Cypriot composer "Yannis Kyriakides incorporated shortwave "numbers station transmissions in his 1999 ConSPIracy cantata.[37]

"Holger Czukay, a student of Stockhausen, was one of the first to use shortwave in a "rock music context.[35] In 1975, German "electronic music band "Kraftwerk recorded a full length "concept album around simulated radiowave and shortwave sounds, entitled "Radio-Activity.[38] "The The's Radio Cineola monthly broadcasts drew heavily on shortwave radio sound.[39]

Shortwave's future[edit]

PC spectrum display of a modern "software defined shortwave receiver

The development of direct broadcasts from satellites has reduced the demand for shortwave receiver hardware, but there are still 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 standards comparable to the FM broadcast band.[40] 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 the BPL frequencies used overlap with shortwave bands, severe distortions can make listening to analog shortwave radio signals near power lines difficult or impossible.[41]

Experts disagree on the future of shortwave. 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 the glory days of shortwave have gone. Religious broadcasters will still use it because they are not too concerned with listening figures".[40]

However Thomas Witherspoon, editor of shortwave news site SWLingPost.com wrote that “shortwave remains the most accessible international communications medium that still provides listeners with the protection of complete anonymity". According to Nigel Fry, head of Distribution for the "BBC World Service Group, “I still see a place for shortwave in the 21st century, especially for reaching areas of the world that are prone to natural disasters that destroy local broadcasting and Internet infrastructure".[40]

See also[edit]


  1. ^ Grundig Satellit 400 international/professional ShortWaveRadio.ch
  2. ^ Inconsistent article: itwissen.info: KW (Kurzwelle) SW (short wave) Quote: "... Der KW-Frequenzbereich (SW) liegt zwischen 3 MHz und 30 MHz [<-1. definition] ... Kurzwelle ist auch eine sendetechnische Bezeichnung für Rundfunk im Frequenzbereich zwischen 2,3 MHz und 26,1 MHz [<-2. definition] ..."
  3. ^ oldtimeradio.de: Kleines Radio-Lexikon Quote: "... Kurzwellen, Kurzwellenbereich ... Wellenbereich, der von den Rundfunksendern (je nach geographischer Lage) von 11 bis 120 m = 26.100 bis 2.300 kHz ..."
  4. ^ darc.de: Amateurfunk Frequenzen Quote: "... Grenzwelle (Kurzwelle) ...", de:Grenzwelle Quote: "... Als Grenzwelle wird der Frequenzbereich zwischen 1605 kHz und 3800 kHz bezeichnet, weil er auf der „Grenze" zwischen Mittelwelle und Kurzwelle liegt ..."
  5. ^ Grundig Satellit 1000 TR6002, schematic See at the bottom of the schematic, just below the transformer. In the schematic it is written that the first shortwave band starts at 1.6 MHz (just after the band end of MW/AM): "KW1-SW1-OC1 1,6 .... 5,0 MHz"
  6. ^ Nebeker, Frederik (6 May 2009). Dawn of the Electronic Age: Electrical Technologies in the Shaping of the Modern World, 1914 to 1945. John Wiley & Sons. pp. 157–. "ISBN "978-0-470-40974-9. 
  7. ^ a b Bray, John (2002). Innovation and the Communications Revolution: From the Victorian Pioneers to Broadband Internet. IET. pp. 73–75. "ISBN "9780852962183. 
  8. ^ Beauchamp, K. G. (2001). History of Telegraphy. IET. p. 234. "ISBN "0-85296-792-6. Retrieved 2007-11-23. 
  9. ^ Burns, R. W. (1986). British Television: The Formative Years. IET. p. 315. "ISBN "0-86341-079-0. Retrieved 2007-11-23. 
  10. ^ "Full text of "Beyond the ionosphere : fifty years of satellite communication"". Archive.org. Retrieved 2012-08-31. 
  11. ^ Peter J. Hugill (4 March 1999). Global Communications Since 1844: Geopolitics and Technology. JHU Press. pp. 129–. "ISBN "978-0-8018-6074-4. 
  12. ^ Cable and Wireless Plc History Archived 2015-03-20 at the "Wayback Machine.
  13. ^ Stormfax. Marconi Wireless on Cape Cod
  14. ^ "1921 – Club Station 1BCG and the Transatlantic Tests". Radio Club of America. Retrieved 2009-09-05. 
  15. ^ "Radio Service Bulletin No. 72, pp. 9–13". Bureau of Navigation, Department of Commerce. 1923-04-02. Retrieved 2009-09-05. 
  16. ^ [1] Archived November 30, 2009, at the "Wayback Machine.
  17. ^ "Recommendations for Regulation of Radio: October 6–10, 1924". Earlyradiohistory.us. Retrieved 2012-08-31. 
  18. ^ http://www.twiar.org/aaarchives/WB008.txt
  19. ^ Karl Rawer:"Wave Propagation in the Ionosphere". Kluwer, Dordrecht 1993 "ISBN "0-7923-0775-5
  20. ^ Panasonic/National ShortwaveRadio.ch
  21. ^ "Feld Hell Club". Google Sites. Google. Retrieved 9 January 2017. 
  22. ^ Ian Robertson Sinclair, Audio and Hi-Fi Handbook, Newnes, 2000 "ISBN "0-7506-4975-5 pp. 195–196
  23. ^ Christopher H. Sterling (March 2004). Encyclopedia of Radio 3-Volume Set. Routledge. pp. 538–. "ISBN "978-1-135-45649-8. 
  24. ^ Hearst Magazines (January 1940). Popular Mechanics. Hearst Magazines. pp. 62–. 
  25. ^ "IARU Monitoring System". iaru.org. International Amateur Radio Union (IARU). Retrieved 28 November 2017. 
  26. ^ Andrew R. Yoder (2002). Pirate Radio Stations: Tuning in to Underground Broadcasts in the Air and Online. McGraw Hill Professional. "ISBN "978-0-07-137563-4. 
  27. ^ Vladimir Bychkov; Gennady Golubkov; Anatoly Nikitin (17 July 2010). The Atmosphere and Ionosphere: Dynamics, Processes and Monitoring. Springer Science & Business Media. pp. 104–. "ISBN "978-90-481-3212-6. 
  28. ^ Nationaal Frequentieplan
  29. ^ http://www.w4uvh.net/dxld7078.txt
  30. ^ Habrat, Marek. "Odbiornik "Roksana" (Radio constructor's recollections)". Retrieved 2008-08-05. 
  31. ^ [2] Archived February 10, 2005, at the "Wayback Machine.
  32. ^ Arlyn T. Anderson. "Changes at the BBC World Service: Documenting the World Service's Move From Shortwave to Web Radio in North America, Australia, and New Zealand", Journal of Radio Studies 2005, Vol. 12, No. 2, Pages 286–304 "doi:10.1207/s15506843jrs1202_8 mentioned in [3] WWCR FAQ
  33. ^ Web-Controlled Radios DXing.com
  34. ^ a b Karl Heinrich Wörner (1973). Stockhausen; Life and Work. University of California Press. pp. 76–. "ISBN "978-0-520-02143-3. 
  35. ^ a b David Sheppard (1 May 2009). On Some Faraway Beach: The Life and Times of Brian Eno. Chicago Review Press. pp. 275–. "ISBN "978-1-55652-107-2. 
  36. ^ a b The Wire. C. Parker. 2000. 
  37. ^ Laura Dolp (13 July 2017). Arvo Pärt's White Light. Cambridge University Press. pp. 83–. "ISBN "978-1-107-18289-9. 
  38. ^ Tim Barr (31 August 2013). Kraftwerk: from Dusseldorf to the Future With Love. Ebury Publishing. pp. 98–. "ISBN "978-1-4481-7776-9. 
  39. ^ Radio Cineola www.thethe.com Archived December 18, 2011, at the "Wayback Machine.
  40. ^ a b c Careless, James. "The Evolution of Shortwave Radio". Radio World. NewBay Media. Retrieved 16 February 2018. 
  41. ^ Halid Hrasnica; Abdelfatteh Haidine; Ralf Lehnert (14 January 2005). Broadband Powerline Communications: Network Design. John Wiley & Sons. pp. 34–. "ISBN "978-0-470-85742-7. 

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