View source for Physics:Shortwave radio

{{short description|Radio transmissions using wavelengths between 10 m and 100 m}}
{{redirect|Shortwave}}
[[File:Grundig Satellit Professional 400.JPG|thumb|right|[[Grundig]] Satellit&nbsp;400 solid-state, digital shortwave receiver, c.&nbsp;1986<ref name=SWRad_GS400/>]]

'''Shortwave radio''' is [[Social:Radio|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 [[Physics:High frequency|high frequency band (HF)]], which extends from 3 to 30&nbsp;MHz (approximately 100 to 10 metres in wavelength). It lies between the [[Physics:Medium frequency|medium frequency band (MF)]] and the bottom of the [[Engineering:Very high frequency|VHF band]].

[[Radio wave]]s in the shortwave band can be reflected or refracted from a layer of electrically charged atoms in the atmosphere called the [[Astronomy:Ionosphere|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 [[Astronomy:Skywave|skywave]] or "skip" [[Physics:Radio propagation|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|line-of-sight propagation]]) and are generally limited by the visual horizon, about 64&nbsp;km (40&nbsp;miles).
[[File:Tesla 623A Máj.png|thumb|Tesla Máj 623A, Short-long-medium wave tube receiver from Czechoslovakia, {{circa|1956}}/57]]

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 [[Social:Propaganda|propaganda tool]] for an international audience. The heyday of [[Social:International broadcasting|international shortwave broadcasting]] was during the [[History:Cold War|Cold War]] between 1960 and 1990. 

With the wide implementation of other technologies for the long-distance distribution of radio programs, such as [[Physics:Satellite radio|satellite radio]], cable broadcasting and [[Internet radio|IP-based transmissions]], shortwave broadcasting lost importance. Initiatives for the digitization of broadcasting did not bear fruit either, and {{asof|2025|lc=yes}}, relatively few broadcasters continue to broadcast programs on shortwave. However, shortwave listening remains a niche hobby, with enthusiasts tuning into fringe stations.

Shortwave radio is important in war zones, such as in the Russo-Ukrainian war,<ref>{{Cite journal |date=March 25, 2022 |title=Why the BBC World Service's New Ukrainian Shortwave Service Matters |url=https://www.rand.org/pubs/commentary/2022/03/why-the-bbc-world-services-new-ukrainian-shortwave-service.html |website=The Rand Blog |last1=Sacks |first1=Benjamin J. }}</ref><ref>{{Cite web |date=February 25, 2022 |title=Ukraine: BBC adds two shortwave broadcasts, NEXUS adds MW service |url=https://swling.com/blog/2022/02/ukraine-bbc-adds-two-shortwave-broadcasts-nexus-adds-mw-service/ |website=The SW Ling Post |access-date=December 4, 2023}}</ref><ref>{{Cite web |date=February 25, 2022 |title=BBC World Service 15735 AM 1400 utc 25 Feb 2022 - new transmission |url=https://www.hfunderground.com/board/index.php/topic,93488.0.html |website=HF Underground |access-date=December 4, 2023}}</ref><ref>{{Cite web |date=March 2, 2022 |title=BBC World Service 5875 kHz Shortwave Russia Ukraine War broadcast |url=https://www.youtube.com/watch?v=nsrOzB2Cfgs |website=YouTube |access-date=December 4, 2023}}</ref><ref>{{cite news |last1=Demianyk |first1=Graeme |title=BBC Revives Old-School Radio Service To Help Ukraine As TV And Internet Attacked |url=https://www.huffingtonpost.co.uk/entry/bbc-ukraine-shortwave-radio-frequencies_uk_621fa132e4b0a7784bb2808f/ |access-date=11 December 2023 |work=HuffPost UK |date=2 March 2022 |language=en}}</ref> 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.

==History==
===Development===
[[File:Guglielmo Marconi 1901 wireless signal.jpg|thumb|right|Radio amateurs carried out the first shortwave transmissions over a long distance before those of [[Biography:Guglielmo Marconi|Guglielmo Marconi]].]]
The name "shortwave" originated during the beginning of radio in the early 20th century, when the [[Physics:Radio spectrum|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 the wavelengths in this band are shorter than 200&nbsp;m (1,500&nbsp;kHz) which marked the original upper limit of the [[Physics:Medium frequency|medium frequency]] band [[History:History of radio|first used]] for radio communications. The broadcast medium wave band now extends above the 200&nbsp;m / 1,500&nbsp;kHz limit.

Early long-distance radio telegraphy used long waves, below 300&nbsp;[[Kilohertz|kilohertz]] (kHz) / above 1000 m. The drawbacks to this system included a very limited spectrum available for long-distance communication, and the very expensive [[Engineering:Transmitter|transmitter]]s, 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&nbsp;MHz were regarded as useless for long-distance communication and were designated in many countries for amateur use.<ref name=Nebeker2009/>

[[Biography:Guglielmo Marconi|Guglielmo Marconi]], pioneer of radio, commissioned his assistant [[Biography:Charles Samuel Franklin|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, [[History:Cornwall|Cornwall]], running on 25&nbsp;kW of power. In June and July&nbsp;1923, wireless transmissions were completed during nights on 97&nbsp;meters (about 3&nbsp;MHz) from Poldhu to Marconi's yacht ''Elettra'' in the Cape Verde Islands.<ref name=Bray2002/>

In September 1924, Marconi arranged for transmissions to be made day and night on 32 meters (about 9.4&nbsp;MHz) from Poldhu to his yacht in the harbour at [[Place:Beirut|Beirut]], to which he had sailed, and was "astonished" to find he could receive signals "throughout the day".<ref>{{cite book |last=Marconi |first=Degna |title=My Father, Marconi |url=https://books.google.com/books?id=vtYy9TLrbA0C&pg=PA207 |publisher=Edizione Frassinelli |location=Toronto / New York |date=1996 |orig-year=1962 |page=207 |isbn=1-55071-044-3}}</ref> Franklin went on to refine the directional transmission by inventing the [[Physics:Curtain array|curtain array]] aerial system.<ref name=Beauchamp2001/><ref name=Franklin_1986/> 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 [[Engineering:Imperial Wireless Chain|Imperial Wireless Chain]]. The UK-to-Canada shortwave "Beam Wireless Service" went into commercial operation on 25&nbsp;October 1926. Beam Wireless Services from the UK to Australia, South Africa and India went into service in 1927.<ref name=Bray2002/>

Shortwave communications began to grow rapidly in the 1920s.<ref name=BeyondIonosph/> By 1928, more than half of long-distance communications had moved from [[Engineering:Submarine communications cable|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.<ref name=Hugill_1999/> However, some commercial longwave communications stations remained in use until 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 the Imperial Wireless and Cable Conference<ref name=PorthCurnoPLC/> 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.

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 use of shortwave propagation===
[[File:Tuning dial, Hallicrafters SX-28.png|thumb|right|[[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 [[Physics:Surface wave|surface wave]] propagation at [[Physics:Very low frequency|very low frequencies]],<ref>{{cite web |website=Stormfax.com |title=Marconi wireless on Cape Cod |url=http://www.stormfax.com/wireless.htm |access-date=2009-05-24 |archive-date=2008-10-24 |archive-url=https://web.archive.org/web/20081024192918/http://www.stormfax.com/wireless.htm |url-status=live}}</ref> which are attenuated along the path at wavelengths shorter than 1,000&nbsp;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&nbsp;1921,<ref name=RCA1921/> operating in the 200&nbsp;meter mediumwave band (near 1,500&nbsp;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&nbsp;meters and at least 20&nbsp;North American amateurs heard amateur signals from Europe. The first two-way communications between North American and Hawaiian amateurs began in 1922 at 200&nbsp;meters. Although operation on wavelengths shorter than 200&nbsp;meters 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 [[Physics:Vacuum tube|vacuum tube]]s shortly after World War&nbsp;I.

Extreme interference at the longer edge of the 150–200&nbsp;meter band – the official wavelengths allocated to amateurs by the Second National Radio Conference<ref name=RadSvcBlt_1923/> in 1923 – forced amateurs to shift to shorter and shorter wavelengths. However, regulations limited amateurs to wavelengths longer than 150&nbsp;meters (2&nbsp;MHz). A few fortunate amateurs who obtained special permission for experimental communications at wavelengths shorter than 150&nbsp;meters completed hundreds of long-distance two-way contacts on 100&nbsp;meters (3&nbsp;MHz) in 1923 including the first transatlantic two-way contacts.<ref name=Raide_1998/>

By 1924 many additional specially licensed amateurs were routinely making transoceanic contacts at distances of 6,000&nbsp;miles (9,600&nbsp;km) and more. On 21&nbsp;September 1924 several amateurs in California completed two-way contacts with an amateur in [[Earth:New Zealand|New Zealand]]. On 19&nbsp;October amateurs in New Zealand and England completed a 90&nbsp;minute two-way contact nearly halfway around the world. On 10&nbsp;October the Third National Radio Conference made three shortwave bands available to U.S. amateurs<ref name=ThirdNRC_1924/> at 80&nbsp;meters (3.75&nbsp;MHz), 40&nbsp;meters (7&nbsp;MHz) and 20&nbsp;meters (14&nbsp;MHz). These were allocated worldwide, while the 10&nbsp;meter band (28&nbsp;MHz) was created by the Washington International Radiotelegraph Conference<ref name=Continelli_1996/> on 25&nbsp;November 1927. The 15&nbsp;meter band (21&nbsp;MHz) was opened to amateurs in the United States on 1&nbsp;May 1952.

==Propagation characteristics==
[[Image:Skip Zone Example.gif|thumb|right|Formation of a [[Physics:Skip zone|skip zone]]]]
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 [[Astronomy:Ionosphere|ionosphere]], (a phenomenon known as "[[Astronomy:Skywave|skywave]] propagation"). A typical phenomenon of shortwave propagation is the occurrence of a [[Physics:Skip zone|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 [[Astronomy:Ionosphere|ionosphere]], propagation often simultaneously occurs on different paths, [[Physics:Scattering|scattered]] by the [[Astronomy:Ionosphere#layers anchor|‘E’ or ‘F’&nbsp;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’&nbsp;layer, may impose a serious limit. This is due to collisions of electrons with neutral molecules, absorbing some of a [[Engineering:Radio frequency|radio frequency]]'s energy and converting it to heat.<ref name=Rawer1993/> Predictions of skywave propagation depend on:
* The distance from the transmitter to the target receiver.
* Time of day. During the day, frequencies higher than approximately 12&nbsp;MHz can travel longer distances than lower ones. At night, this property is reversed.
* With lower frequencies the dependence on the time of the day is mainly due to the lowest ionospheric layer, the ‘D’ Layer, forming only during the day when photons from the sun break up atoms into ions and free electrons.
* Season. During the winter months of the Northern or Southern hemispheres, the AM/MW broadcast band tends to be more favorable because of longer hours of darkness.
* [[Astronomy:Solar flare|Solar flare]]s produce a large increase in D region ionization – so great, sometimes for periods of several minutes, that skywave propagation is nonexistent.

==Types of modulation==
 [[Image:Shortwave Radio.jpg|thumb|right|[[National Panasonic]] R3000 [[Engineering:Analogue electronics|analog]] shortwave [[Engineering:Radio receiver|radio receiver]], {{Circa|1965}}<ref name=SWRad_Panasonic/>]]
Several different types of [[Engineering:Modulation|modulation]] are used to incorporate information in a short-wave signal.

===Audio modes===
====AM====
[[Physics:Amplitude modulation|Amplitude modulation]] is the simplest type and the most commonly used for [[Social:International broadcasting|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 [[Engineering:Detector (radio)|detector]] recovers the desired modulation signal from the carrier.<ref name=RohdeWhitaker2000/>

====SSB====
[[Physics:Single-sideband modulation|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|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 {{frac|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 (signal processing)|bandwidth]], enabling less than one-half the AM signal bandwidth to be used.<ref name=RohdeWhitaker2000/>

The drawback is the receiver is more complicated, because it must recreate 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) is customarily used below 10&nbsp;MHz and USB (upper sideband) above 10&nbsp;MHz, non-amateur services use USB regardless of frequency.

====VSB====
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 is that only half the bandwidth of an AM signal is used. It is used by the Canadian standard time signal station CHU. [[Physics:Single-sideband modulation#Vestigial sideband (VSB)|Vestigial sideband]] was used for analog television and by [[ATSC standards|ATSC]], the [[Physics:8VSB|digital TV]] system used in North America.

====NFM====
Narrow-band [[Physics:Frequency modulation|frequency modulation]] (NBFM or NFM) is used typically above 20&nbsp;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.<ref name=Sinclair2000/>

====DRM====
Digital Radio Mondiale (DRM) is a digital modulation for use on bands below 30&nbsp;MHz. It is a digital signal, like the data modes, below, but is for transmitting audio, like the analog modes above.

===Data modes===
====CW====
[[Continuous wave]] (CW) is [[Engineering:On-off keying|on-and-off keying]] of a sine-wave carrier, used for [[Engineering:Morse code|Morse code]] communications and [[Engineering:Hellschreiber|Hellschreiber]] [[Social:Facsimile|facsimile]]-based [[Engineering:Teleprinter|teleprinter]] transmissions. It is a data mode, although often listed separately.<ref name=FeldHellFAQ/> It is typically received via lower or upper SSB modes.<ref name=RohdeWhitaker2000/>

====RTTY, FAX, SSTV====
[[Engineering:Radioteletype|Radioteletype]], fax, digital, [[Physics:Slow-scan television|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.

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.

==Users==
[[File:Shortwave_Radio_Dial.jpg|thumb|right|Portable shortwave receiver's [[digital display]] tuned to the 75&ndash;meter band]]
Some established users of the shortwave radio bands may include:
* [[Social:International broadcasting|International broadcasting]] primarily by government-sponsored [[Social:Propaganda|propaganda]], or international news (for example, the BBC World Service), religious or cultural stations to foreign audiences: The most common use of all.
* Domestic broadcasting: to widely dispersed populations with few longwave, mediumwave and FM stations serving them; or for speciality political, religious and alternative media networks; or of individual commercial and non-commercial paid broadcasts.
* Oceanic [[Engineering:Air traffic control|air traffic control]] uses the HF/shortwave band for long-distance communication to aircraft over the oceans and poles, which are far beyond the range of traditional VHF frequencies. Modern systems also include satellite communications, such as ADS-C/CPDLC.
* Two-way radio communications by marine and maritime HF stations, aeronautical users, and ground based stations.<ref name="Ilčev">{{cite book |last1=Ilčev |first1=Stojče Dimov |title=Global Aeronautical Distress and Safety Systems (GADSS): Theory and Applications |url=https://books.google.com/books?id=SWvDDwAAQBAJ&q=shortwave+communications+users&pg=PA310 |date=10 December 2019 |publisher=Springer Nature |isbn=9783030306328 |access-date=9 September 2021 |archive-date=25 January 2022 |archive-url=https://web.archive.org/web/20220125091407/https://books.google.com/books?id=SWvDDwAAQBAJ&q=shortwave+communications+users&pg=PA310 |url-status=live }}</ref> For example, two way shortwave communication is still used in remote regions by the Royal Flying Doctor Service of Australia.<ref name="Berg4">{{cite book |last1=Berg |first1=Jerome S. |title=The Early Shortwave Stations: A Broadcasting History Through 1945 |url=https://books.google.com/books?id=XSWXAAAAQBAJ&q=flying+doctors+australia+shortwave&pg=PA162 |date=20 September 2013 |publisher=McFarland |isbn=9780786474110 |access-date=9 September 2021 |archive-date=25 January 2022 |archive-url=https://web.archive.org/web/20220125091416/https://books.google.com/books?id=XSWXAAAAQBAJ&q=flying+doctors+australia+shortwave&pg=PA162 |url-status=live }}</ref>
* "Utility" stations transmitting messages not intended for the general public, such as merchant shipping, marine weather, and ship-to-shore stations; for aviation weather and air-to-ground communications; for military communications; for long-distance governmental purposes, and for other non-broadcast communications.
* Amateur radio operators at the 80/75, 60, 40, 30, 20, 17, 15, 12, and 10&ndash;meter bands. Licenses are granted by authorized government agencies.
* Time signal and [[Physics:Radio clock|radio clock]] stations: In North America, WWV radio and WWVH radio transmit at these frequencies: 2.5&nbsp;MHz, 5&nbsp;MHz, 10&nbsp;MHz, and 15&nbsp;MHz; and WWV also transmits on 20&nbsp;MHz. The CHU radio station in Canada transmits on the following frequencies: 3.33&nbsp;MHz, 7.85&nbsp;MHz, and 14.67&nbsp;MHz. Other similar [[Physics:Radio clock|radio clock]] stations transmit on various shortwave and longwave frequencies around the world. The shortwave transmissions are primarily intended for human reception, while the longwave stations are generally used for automatic synchronization of watches and clocks.

Sporadic or non-traditional users of the shortwave bands may include:
* Clandestine stations. These are stations that broadcast on behalf of various political movements such as rebel or insurrectionist forces. They may advocate civil war, insurrection, rebellion against the government-in-charge of the country to which they are directed. Clandestine broadcasts may emanate from transmitters located in rebel-controlled territory or from outside the country entirely, using another country's transmission facilities.<ref name=Sterling2004/>
* Numbers stations. These stations regularly appear and disappear all over the shortwave radio band, but are unlicensed and untraceable. It is believed that numbers stations are operated by government agencies and are used to communicate with clandestine operatives working within foreign countries. However, no definitive proof of such use has emerged. Because the vast majority of these broadcasts contain nothing but the recitation of blocks of numbers, in various languages, with occasional bursts of music, they have become known colloquially as "number stations". Perhaps the most noted number station is called the "Lincolnshire Poacher", named after the 18th&nbsp;century English folk song, which is transmitted just before the sequences of numbers.
* Unlicensed two way radio activity by individuals such as taxi drivers, bus drivers and fishermen in various countries can be heard on various shortwave frequencies. Such unlicensed transmissions by "pirate" or "bootleg" two way radio operators<ref name=PopMech1940Jan/> can often cause [[Physics:Co-channel interference|signal interference]] to licensed stations.  Unlicensed business radio (taxis, trucking companies, among numerous others) land mobile systems may be found in the 20–30&nbsp;MHz region while unlicensed marine mobile and other similar users may be found over the entire shortwave range.<ref name=IARU/>
* Pirate radio broadcasters who feature programming such as music, talk and other entertainment, can be heard sporadically and in various modes on the shortwave bands. Pirate broadcasters take advantage of the better propagation characteristics to achieve more range compared to the AM or FM broadcast bands.<ref name="Yoder2002">{{cite book |first=Andrew R. |last=Yoder |title=Pirate Radio Stations: Tuning in to underground broadcasts in the Air and Online |url=https://books.google.com/books?id=qMjT5wOX-d4C |year=2002 |publisher=McGraw Hill Professional |isbn=978-0-07-137563-4 |access-date=2017-11-28 |archive-date=2020-08-19 |archive-url=https://web.archive.org/web/20200819202519/https://books.google.com/books?id=qMjT5wOX-d4C |url-status=live }}</ref>
* [[Engineering:Over-the-horizon radar|Over-the-horizon radar]]: From 1976 to 1989, the [[Place:Soviet Union|Soviet Union]]'s Russian Woodpecker over-the-horizon radar system blotted out numerous shortwave broadcasts daily.
* [[Astronomy:Ionospheric heater|Ionospheric heater]]s used for scientific experimentation such as the [[Astronomy:High Frequency Active Auroral Research Program|High Frequency Active Auroral Research Program]] in Alaska, and the [[Organization:Sura Ionospheric Heating Facility|Sura ionospheric heating facility]] in Russia.<ref name=BychkovGolubkov2010/>
* High-frequency trading firms have asked the FCC to open shortwave frequencies to datacasting that would allow faster data transmission than fiber optic cables.<ref>{{Cite web |last=Langan |first=Nick |date=2025-04-10 |title=Mystery Surrounds 3 Pending U.S. Shortwave Stations |url=https://www.radioworld.com/news-and-business/business-and-law/mystery-surrounds-3-pending-u-s-shortwave-stations |url-status=live |archive-url=https://web.archive.org/web/20250522192614/https://www.radioworld.com/news-and-business/business-and-law/mystery-surrounds-3-pending-u-s-shortwave-stations |archive-date=2025-05-22 |access-date=2025-05-22 |website=Radio World |language=en-US}}</ref><ref>{{Cite web |last=Schneider |first=David |date=2018-06-01 |title=Wall Street Tries Shortwave Radio to Make High-Frequency Trades Across the Atlantic - IEEE Spectrum |url=https://spectrum.ieee.org/wall-street-tries-shortwave-radio-to-make-highfrequency-trades-across-the-atlantic |url-status=live |archive-url=https://web.archive.org/web/20250522192844/https://spectrum.ieee.org/wall-street-tries-shortwave-radio-to-make-highfrequency-trades-across-the-atlantic |archive-date=2025-05-22 |access-date=2025-05-22 |website=spectrum.ieee.org |language=en}}</ref><ref>{{Cite web |last=Osipovich |first=Alexander |date=2023-08-05 |title=Ham Radio Enthusiasts vs. High-Frequency Traders: A Battle for the Airwaves |url=https://www.wsj.com/business/entrepreneurship/ham-radio-enthusiasts-vs-high-frequency-traders-a-battle-for-the-airwaves-6d6c5c1f |url-status=live |archive-url=https://web.archive.org/web/20250522191932/https://www.wsj.com/business/entrepreneurship/ham-radio-enthusiasts-vs-high-frequency-traders-a-battle-for-the-airwaves-6d6c5c1f |archive-date=2025-05-22 |access-date=2025-05-22 |website=WSJ |language=en-US}}</ref> Concerns about the reliability, capacity, security and [[Finance:Stock market crash|contagion risk]] presented by this use of shortwave technology have been raised.<ref>{{Cite web |last=Brown |first=Aaron |date=2023-10-20 |title=Could Speedier High-Frequency Trading Prompt the Next Market Meltdown? |url=https://www.garp.org/risk-intelligence/technology/speedy-trading-meltdown-102023 |url-status=live |archive-url=https://web.archive.org/web/20250522193826/https://www.garp.org/risk-intelligence/technology/speedy-trading-meltdown-102023 |archive-date=2025-05-22 |access-date=2025-05-22 |website=www.garp.org |language=en}}</ref>

==Shortwave broadcasting<span class="anchor" id="shortwave_broadcasting_anchor"></span>==
[[File:Indoor shot of Pori short wave station, 1954.jpg|thumb|Transmitter room of shortwave station [[Yle]] in Pori, Finland, in 1954]]

* ''See [[Social:International broadcasting|International broadcasting]] for details on the history and practice of broadcasting to foreign audiences.''
* ''See List of shortwave radio broadcasters for a list of international and domestic shortwave radio broadcasters.''
* ''See [[Physics:Shortwave relay station|Shortwave relay station]] for the actual kinds of integrated technologies used to bring high power signals to listeners.''

===Frequency allocations===
The [[Organization:World Radiocommunication Conference|World Radiocommunication Conference]] (WRC), organized under the auspices of the [[Organization:International Telecommunication Union|International Telecommunication Union]], allocates bands for various services in conferences every few years. The last WRC took place in 2023.<ref>{{Cite web |title=WRC-23 – World Radiocommunication Conferences (WRC) |url=https://www.itu.int/wrc-23/ |access-date=2024-05-13 |language=en}}</ref>

As of WRC-97 in 1997, these bands were allocated for [[Social:International broadcasting|international broadcasting]]. AM shortwave broadcasting channels are allocated with a 5&nbsp;kHz separation for traditional analog audio broadcasting:
{{Clear}}
{| border="0" cellspacing="2" cellpadding="1" style="float:left;margin-left:10px"
|-
! style="background:#b5b5b5;"| Metre Band
! style="background:#b5b5b5;"| Frequency Range
! style="background:#b5b5b5;"| Remarks
|-
| 120&nbsp;m
| 2.3–2.495&nbsp;MHz
| tropical band
|- style="background:#e8e8e8;"
|| 90&nbsp;m
|| 3.2–3.4&nbsp;MHz
|| tropical band
|-
| 75&nbsp;m
| 3.9–4&nbsp;MHz
| shared with the North American amateur radio 80m band
|- style="background:#e8e8e8;"
|| 60&nbsp;m
|| 4.75–5.06&nbsp;MHz
|| tropical band
|-
| 49&nbsp;m
| 5.9–6.2&nbsp;MHz
| &nbsp;
|- style="background:#e8e8e8;"
||  41&nbsp;m
|| 7.2–7.6&nbsp;MHz
|| shared with the amateur radio 40m band
|-
| 31&nbsp;m
| 9.4–9.9&nbsp;MHz
| the most heavily used band
|- style="background:#e8e8e8;"
|| 25&nbsp;m
|| 11.6–12.2&nbsp;MHz
|| &nbsp;
|-
| 22&nbsp;m
| 13.57–13.87&nbsp;MHz
|
|- style="background:#e8e8e8;"
|| 19&nbsp;m
|| 15.1–15.8&nbsp;MHz
|| &nbsp;
|-
| 16&nbsp;m
| 17.48–17.9&nbsp;MHz
| &nbsp;
|- style="background:#e8e8e8;"
|| 15&nbsp;m
|| 18.9–19.02&nbsp;MHz
|| almost unused, could become a DRM band
|-
| 13&nbsp;m
| 21.45–21.85&nbsp;MHz
| &nbsp;
|- style="background:#e8e8e8;"
|| 11&nbsp;m
|| 25.6–26.1&nbsp;MHz
|| may be used for local DRM broadcasting
|}
{{Clear}}
[[File:Shortwave and other bands on World Radio receiver.jpg|thumb|right|Tuning display of a cheap portable "World Radio" which includes nine shortwave bands]]
Although countries generally follow the assigned bands, there may be small differences between countries or regions. For example, in the official bandplan of the Netherlands,<ref name=RijksOverheid2007/> the 49&nbsp;m band starts at 5.95&nbsp;MHz, the 41&nbsp;m band ends at 7.45&nbsp;MHz, the 11&nbsp;m band starts at 25.67&nbsp;MHz, and the 120&nbsp;m, 90&nbsp;m, and 60&nbsp;m bands are absent altogether. International broadcasters sometimes operate outside 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&nbsp;m, 49&nbsp;m, 40&nbsp;m, 41&nbsp;m, 31&nbsp;m, 25&nbsp;m).

The new digital audio broadcasting format for shortwave DRM operates 10&nbsp;kHz or 20&nbsp;kHz channels. There are some ongoing discussions with respect to specific band allocation for DRM, as it mainly transmitted in 10&nbsp;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 [[Engineering:Over-the-horizon radar|over-the-horizon radar]]. Shortwave transmitting centers often use specialized [[Engineering:Antenna (radio)|antenna]] designs (like the [[Engineering:ALLISS|ALLISS]] antenna technology) to concentrate radio energy at the target area.

===Advantages===
[[File:Soviet SWL URS3-108-B.jpeg|thumb|right|[[Soviet Union|Soviet]] shortwave listener (A. Kozlov, URS3-108-B) in Borisoglebsk, 1941]]
Shortwave possesses a number of advantages over newer technologies:
* Difficulty of censoring programming by authorities in restrictive countries. Unlike their relative ease in monitoring and [[Internet censorship|censoring the Internet]], over-the air television, cable television, satellite television, satellite radio, mobile phones, landline phones, and satellite phones, government authorities face technical difficulties monitoring which stations (sites) are being listened to (accessed). For example, during the attempted coup against Soviet President [[Biography:Mikhail Gorbachev|Mikhail Gorbachev]], when his access to communications was limited (e.g. his phones, television and radio were cut off), Gorbachev was able to stay informed by means of the BBC World Service on shortwave.<ref name=w4uvh/>
* Low-cost shortwave radios are widely available in all but the most repressive countries in the world. Simple shortwave regenerative receivers can be easily built with a few parts.
* In many countries (particularly in most developing nations and in the Eastern bloc during the [[History:Cold War|Cold War]] era) ownership of shortwave receivers has been and continues to be widespread<ref name=Habrat_recollections/> (in many of these countries some domestic stations also used shortwave).
* Many newer shortwave receivers are portable and can be battery-operated, making them useful in difficult circumstances. Newer technology includes hand-cranked radios which provide power without batteries.
* Shortwave radios can be used in situations where [[Engineering:Terrestrial television|over-the-air television]], [[Engineering:Cable television|cable television]], [[Engineering:Satellite television|satellite television]], [[Engineering:Landline|landline phones]], mobile phones, satellite phones, [[Astronomy:Communications satellite|satellite communications]], or the [[Internet]] is temporarily, long-term or permanently unavailable (or unaffordable).
* Shortwave radio travels much farther than broadcast FM (88–108&nbsp;MHz). Shortwave broadcasts can be easily transmitted over a distance of several thousand miles, including from one continent to another.
* Particularly in tropical regions, SW is somewhat less prone to interference from thunderstorms than medium wave radio, and is able to cover a large geographic area with relatively low power (and hence cost). Therefore, in many of these countries it is widely used for domestic broadcasting.
* Very little infrastructure is required for long-distance two-way communications using shortwave radio. All one needs is a pair of transceivers, each with an antenna, and a source of energy (such as a battery, a portable generator, or the electrical grid). This makes shortwave radio one of the most robust means of communications, which can be disrupted only by interference or bad ionospheric conditions. Modern digital transmission modes such as MFSK and Olivia are even more robust, allowing successful reception of signals well below the [[Physics:Noise floor|noise floor]] of a conventional receiver.

===Disadvantages===
Shortwave radio's benefits are sometimes regarded as being outweighed by its drawbacks, including:
* In most Western countries, shortwave radio ownership is usually limited to enthusiasts, since most new standard radios do not receive the shortwave band. Therefore, Western audiences are limited.
* In the developed world, shortwave reception is very difficult in urban areas because of excessive noise from [[Engineering:Switched-mode power supply|switched-mode]] power adapters, fluorescent or LED light sources, internet modems and routers, computers and many other sources of radio interference.
* Audio quality may be limited due to interference and the modes that are used.

==Shortwave listening==
[[File:RADIOBUDAPESTPENNANTLATE80s.JPG|thumb|right|A pennant sent to overseas listeners by [[Magyar Rádió|Radio Budapest]] in the late 1980s]]
The Asia-Pacific Telecommunity estimates that there are approximately 600&nbsp;million shortwave broadcast-radio receivers in use in 2002.<ref name=AptSec2002/> WWCR claims that there are 1.5&nbsp;billion shortwave receivers worldwide.<ref name=Anderson2005/>

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 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.<ref>{{cite web |url=https://wiki.radioreference.com/index.php/Live_Tunable_Receivers |title=Live tunable receivers |website=The Radio Reference Wiki |access-date=2020-01-02 |archive-date=2020-01-02 |archive-url=https://web.archive.org/web/20200102180408/https://wiki.radioreference.com/index.php/Live_Tunable_Receivers |url-status=live }}</ref> 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.<ref>{{Cite web |date=2010-03-08 |title=Whatever Happened to Shortwave Radio? |url=https://www.radioworld.com/news-and-business/whatever-happened-to-shortwave-radio |access-date=2022-03-18 |website=Radio World |language=en-US}}</ref>

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==
[[File:Stockhausen 1994 WDR.jpg|thumb|right|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.<ref name=Wörner1973/><ref name=Sheppard2009/>

The first attempts by serious composers to incorporate radio effects into music may be those of the Russian physicist and musician Léon Theremin,<ref name=Wire2000/> who perfected a form of radio oscillator as a musical instrument in 1928 ([[Engineering:Regenerative circuit|regenerative circuit]]s in radios of the time were prone to breaking into [[Oscillation|oscillation]], adding various tonal harmonics to music and speech); and in the same year, the development of a French instrument called the [[Engineering:Ondes Martenot|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 the Beethoven Bicentennial in ''Opus&nbsp;1970'' with filtered and distorted snippets of Beethoven pieces – ''Spiral'' (1968), ''Pole'', ''Expo'' (both 1969–1970), and ''Michaelion'' (1997).<ref name=Wörner1973/>

[[Place:Cyprus|Cypriot]] composer Yannis Kyriakides incorporated shortwave numbers station transmissions in his 1999 ''ConSPIracy cantata''.<ref name=Dolp2017/>

Holger Czukay, a student of Stockhausen, was one of the first to use shortwave in a rock music context.<ref name=Sheppard2009/> In 1975, German [[Physics:Electronic music|electronic music]] band Kraftwerk recorded a full length concept album around simulated radiowave and shortwave sounds, entitled ''Radio-Activity''.<ref name=Barr2013/> The The's Radio Cineola monthly broadcasts drew heavily on shortwave radio sound.<ref name=thethe2011/>

==Shortwave's future==
[[File:Penny Mercury.jpg|thumb|right|PC spectrum display of a modern [[software-defined radio|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 adequate.<ref name=Careless2018/><ref>{{Cite book|last=Amaral|first=Cristiano Torres|title=Guia Moderno do Radioescuta|publisher=Amazon|year=2021}}</ref> 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.<ref name=HrasnicaHaidine2005/>

According to Andy Sennitt, former editor of the ''[[Organization:World Radio TV Handbook|World Radio TV Handbook]]'',

{{quote|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.<ref name=Careless2018/>}}

However, Thomas Witherspoon, editor of shortwave news site ''SWLingPost.com'' wrote that

{{quote|shortwave remains the most accessible international communications medium that still provides listeners with the protection of complete anonymity.<ref>{{cite news |last=Witherspoon |first=Thomas |title=[no title cited] |website=SWLingPost.com}} </ref>}}

In 2018, Nigel Fry, head of Distribution for the BBC World Service Group,

{{quote|I still see a place for shortwave in the 21st&nbsp;century, especially for reaching areas of the world that are prone to natural disasters that destroy local broadcasting and Internet infrastructure.<ref name=Careless2018/>}}

During the 2022 Russian invasion of Ukraine, the BBC World Service launched two new shortwave frequencies for listeners in Ukraine and Russia, broadcasting English-language news updates in an effort to avoid censorship by the Russian state.<ref name=BBC2022/> American commercial shortwave broadcasters WTWW and WRMI also redirected much of their programming to Ukraine.<ref>{{Cite web |last=Wilbanks |first=Kase |title=Lubbock radio DJ reaching Ukraine on shortwave WTWW with truth, hope, classic hits |url=https://www.kcbd.com/2022/04/04/lubbock-radio-dj-reaching-ukraine-shortwave-wtww-with-truth-hope-classic-hits/ |access-date=2022-11-10 |website=KCBD |date=4 April 2022 |language=en}}</ref><ref>{{Cite web |last=Little • • |first=Joe |title=San Diego Radio Host Broadcasts from His Closet for Listeners in Ukraine |url=https://www.nbcsandiego.com/news/local/san-diego-radio-host-broadcasts-from-his-closet-for-listeners-in-ukraine/2910336/ |access-date=2022-11-10 |website=NBC 7 San Diego |date=April 2022 |language=en-US}}</ref><ref>[https://miami.cbslocal.com/2022/03/17/shortwave-radio-signal-central-florida-russia-news/ Shortwave Radio Signal From Florida Cow Pasture Reaches Russia Carrying Latest News] WFOR-TV, March 17, 2022</ref>

==See also==
* [[Engineering:ALLISS|ALLISS]]–a very large rotatable antenna system used in international broadcasting
* List of American shortwave broadcasters
* [[Engineering:List of European short wave transmitters|List of European short wave transmitters]]
* List of shortwave radio broadcasters

== References ==
{{reflist|25em|refs=

<ref name=Anderson2005>{{cite journal |first=Arlyn T. |last=Anderson |title=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=Journal of Radio Studies |year=2005 |volume=12 |issue=2 |pages=286–304 |doi=10.1207/s15506843jrs1202_8|s2cid=154174203}} cited in {{cite web |url=http://www.wwcr.com/wwcr_faq/latest_sw_rx_research.html |title=WWCR FAQ |access-date=8 February 2007 |url-status=dead |archive-url=https://web.archive.org/web/20061114204007/http://www.wwcr.com/wwcr_faq/latest_sw_rx_research.html |archive-date=14 November 2006 |df=dmy-all}}</ref>

<ref name=AptSec2002>{{cite web |url=http://www.aptsec.org/meetings/2002/apg2003-4/(56)ABU.doc |title=[no title cited] |website=aptsec.org |archive-url=https://web.archive.org/web/20050210001613/http://www.aptsec.org/meetings/2002/apg2003-4/(56)ABU.doc |archive-date=10 February 2005 |df=dmy-all}}</ref>

<ref name=Barr2013>{{cite book |first=Tim |last=Barr |title=Kraftwerk: From Dusseldorf to the future with love |url=https://books.google.com/books?id=0mcj4h2qEhQC&pg=PT98 |date=31 August 2013 |publisher=Ebury Publishing |isbn=978-1-4481-7776-9 |pages=98 ff |access-date=16 February 2018 |archive-date=18 August 2020 |archive-url=https://web.archive.org/web/20200818162743/https://books.google.com/books?id=0mcj4h2qEhQC&pg=PT98 |url-status=live}}</ref>

<ref name=Beauchamp2001>{{cite book |url=https://books.google.com/books?id=ni7lDl3k5LwC&q=charles+samuel+franklin&pg=PA234 |title=History of Telegraphy |first=K.G. |last=Beauchamp |year=2001 |publisher=IET |access-date=23 November 2007 |df=dmy-all |isbn=0-85296-792-6 |page=234 |archive-date=25 January 2022 |archive-url=https://web.archive.org/web/20220125091427/https://books.google.com/books?id=ni7lDl3k5LwC&q=charles+samuel+franklin&pg=PA234 |url-status=live}}</ref>

<ref name=BeyondIonosph>{{cite book |url=https://archive.org/stream/beyondionosphere00unitrich/beyondionosphere00unitrich_djvu.txt |type=full text |title=Beyond the Ionosphere: Fifty years of satellite communication |year=1997 |isbn=9780160490545 |via=Archive.org |access-date=31 August 2012 |df=dmy-all |last1=Butrica |first1=Andrew J. |publisher=National Aeronautics and Space Administration, NASA History Office }} </ref>

<ref name=Bray2002>{{cite book |url=https://books.google.com/books?id=3h7R36Y0yFUC |title=Innovation and the Communications Revolution: From the Victorian pioneers to broadband Internet |first=John |last=Bray |year=2002 |publisher=IET |pages=73–75 |isbn=9780852962183 |access-date=11 October 2015 |archive-date=29 April 2016 |archive-url=https://web.archive.org/web/20160429130703/https://books.google.com/books?id=3h7R36Y0yFUC |url-status=live}}</ref>

<ref name=BychkovGolubkov2010>{{cite book |last1=Bychkov |first1=Vladimir |last2=Golubkov |first2=Gennady |last3=Nikitin |first3=Anatoly |title=The Atmosphere and Ionosphere: Dynamics, processes and monitoring |url=https://books.google.com/books?id=rrSgz8l0EI0C&pg=PA104 |date=17 July 2010 |publisher=Springer Science & Business Media |isbn=978-90-481-3212-6 |pages=104 ff |access-date=28 November 2017 |archive-date=19 August 2020 |archive-url=https://web.archive.org/web/20200819210940/https://books.google.com/books?id=rrSgz8l0EI0C&pg=PA104 |url-status=live}}</ref>

<ref name=Careless2018>{{cite magazine |last=Careless |first=James |title=The evolution of shortwave radio |url=http://www.radioworld.com/digital-radio/0014/the-evolution-of-shortwave-radio/338422 |magazine=Radio World |publisher=NewBay Media |access-date=16 February 2018 |archive-date=16 February 2018 |archive-url=https://web.archive.org/web/20180216143819/http://www.radioworld.com/digital-radio/0014/the-evolution-of-shortwave-radio/338422 |url-status=live}}</ref>

<ref name=Continelli_1996>{{cite web |url=http://www.twiar.org/aaarchives/WB008.txt |title=Article&nbsp;#8 |website=twiar.org |series=The Wayback Machine |publisher=Schenectady Museum Amateur Radio Club |last=Continelli |first=Bill, W2XOY |year=1996 |access-date=2 July 2007 |archive-date=10 June 2007 |archive-url=https://web.archive.org/web/20070610094945/http://www.twiar.org/aaarchives/WB008.txt |url-status=live}} Historical note discusses an International Radiotelegraph Conference on 4&nbsp;October 1927, its intrigues and fallout.</ref>

<ref name=Dolp2017>{{cite book |last=Dolp |first=Laura |title=Arvo Pärt's White Light |url=https://books.google.com/books?id=l8wnDwAAQBAJ&pg=PA83 |date=13 July 2017 |publisher=Cambridge University Press |isbn=978-1-107-18289-9 |pages=83 ff |access-date=22 February 2018 |archive-date=19 August 2020 |archive-url=https://web.archive.org/web/20200819141118/https://books.google.com/books?id=l8wnDwAAQBAJ&pg=PA83 |url-status=live}}</ref>

<ref name=FeldHellFAQ>{{cite web |title=Feld Hell Club |url=https://sites.google.com/site/feldhellclub/Home/feld-hell-faq |website=Google Sites |access-date=9 January 2017 |archive-date=10 January 2017 |archive-url=https://web.archive.org/web/20170110090905/https://sites.google.com/site/feldhellclub/Home/feld-hell-faq |url-status=live}}</ref>

<ref name=Franklin_1986>{{cite book |url=https://books.google.com/books?id=WC2MNgNMJ7gC&q=%22charles+samuel+franklin%22&pg=PA315 |title=British Television: The formative years |first=R.W. |last=Burns |year=1986 |access-date=23 November 2007 |df=dmy-all |publisher=IET |isbn=0-86341-079-0 |page=315 |archive-date=25 January 2022 |archive-url=https://web.archive.org/web/20220125091408/https://books.google.com/books?id=WC2MNgNMJ7gC&q=%22charles+samuel+franklin%22&pg=PA315 |url-status=live}}</ref>

<ref name=Habrat_recollections>{{cite web |last=Habrat |first=Marek |title=Odbiornik "Roksana" |trans-title=Radio constructor's recollections |url=http://oldradio.pl/karta_odb.php?nrmod=471 |access-date=5 August 2008 |df=dmy-all |archive-date=6 June 2009 |archive-url=https://web.archive.org/web/20090606060021/http://oldradio.pl/karta_odb.php?nrmod=471 |url-status=live}}</ref>

<ref name=HrasnicaHaidine2005>{{cite book |last1=Hrasnica |first1=Halid |last2=Haidine |first2=Abdelfatteh |last3=Lehnert |first3=Ralf |title=Broadband Powerline Communications: Network design |url=https://books.google.com/books?id=d270N6yvWCoC&pg=PA34 |date=14 January 2005 |publisher=[[Company:John Wiley & Sons|John Wiley & Sons]] |isbn=978-0-470-85742-7 |pages=34 ff |access-date=16 February 2018 |archive-date=19 August 2020 |archive-url=https://web.archive.org/web/20200819030422/https://books.google.com/books?id=d270N6yvWCoC&pg=PA34 |url-status=live}}</ref>

<ref name=Hugill_1999>{{cite book |first=Peter J. |last=Hugill |title=Global Communications Since 1844: Geopolitics and technology |url=https://books.google.com/books?id=GjfBkup-ccMC&pg=PA129 |date=4 March 1999 |publisher=Johns Hopkins University Press |isbn=978-0-8018-6074-4 |pages=129 ff |access-date=16 February 2018 |archive-date=19 August 2020 |archive-url=https://web.archive.org/web/20200819111145/https://books.google.com/books?id=GjfBkup-ccMC&pg=PA129 |url-status=live}}</ref>

<ref name=IARU>{{cite web |title=IARU Monitoring System |url=http://www.iaru.org/monitoring-system.html |website=iaru.org |publisher=International Amateur Radio Union (IARU) |access-date=28 November 2017 |archive-date=1 December 2017 |archive-url=https://web.archive.org/web/20171201040802/http://www.iaru.org/monitoring-system.html |url-status=live}}</ref>

<ref name=Nebeker2009>{{cite book |first=Frederik |last=Nebeker |title=Dawn of the Electronic Age: Electrical Technologies in the Shaping of the Modern World, 1914 to 1945 |url=https://books.google.com/books?id=xwmH6-q5O5AC&pg=PA157 |date=6 May 2009 |publisher=John Wiley & Sons |isbn=978-0-470-40974-9 |pages=157 ff |access-date=8 November 2016 |archive-date=20 August 2020 |archive-url=https://web.archive.org/web/20200820023653/https://books.google.com/books?id=xwmH6-q5O5AC&pg=PA157 |url-status=live}}</ref>

<ref name=PopMech1940Jan>{{cite book |title=Popular Mechanics |url=https://books.google.com/books?id=3tkDAAAAMBAJ&pg=PA62 |date=January 1940 |publisher=Hearst Magazines |pages=62 ff |access-date=28 November 2017 |archive-date=17 December 2019 |archive-url=https://web.archive.org/web/20191217041122/https://books.google.com/books?id=3tkDAAAAMBAJ&pg=PA62 |url-status=live}}</ref>

<ref name=PorthCurnoPLC>{{cite web |url=https://medium.com/@carcbradio/cable-companies-595de8871f6b |title=Cable and wireless PLC history |archive-url=https://web.archive.org/web/20150320053915/http://www.porthcurno.org.uk/page.php?id=104 |archive-date=20 March 2015 |df=dmy-all}}</ref>

<ref name=RadSvcBlt_1923>{{cite magazine |url=https://babel.hathitrust.org/cgi/pt?id=uiug.30112106763342;view=1up;seq=63 |title=Radio Service Bulletin No.&nbsp;72 |pages=9–13 |access-date=5 September 2009 |date=2 April 1923 |df=dmy-all |department=Bureau of Navigation |publisher=Department of Commerce |archive-date=22 November 2018 |archive-url=https://web.archive.org/web/20181122145807/https://babel.hathitrust.org/cgi/pt?id=uiug.30112106763342;view=1up;seq=63 |url-status=live |magazine=Radio service bulletin}}</ref>

<ref name=Raide_1998>{{cite web |last1=Raide |first1=Bob, W2ZM |last2=Gable |first2=Ed, K2MP |title=Celebrating the first trans-Atlantic QSO! |url=http://www.arrl.org/news/features/1998/1102/2/?nc=1 |date=2 November 1998 |publisher=American Radio Relay League |location=Newington, CT |archive-url=https://web.archive.org/web/20091130112737/http://www.arrl.org/news/features/1998/1102/2/?nc=1 |archive-date=30 November 2009 |df=dmy-all}}</ref>

<ref name=Rawer1993>{{cite book |first=Karl |last=Rawer |title=Wave Propagation in the Ionosphere |publisher=Kluwer |place=Dordrecht |year=1993 |isbn=0-7923-0775-5}}</ref>

<ref name=RCA1921>{{cite web |url=http://www.radio-club-of-america.org/history.php?page=1921.html |title=1921 – Club station 1BCG and the transatlantic tests |access-date=5 September 2009 |publisher=Radio Club of America |df=dmy-all |archive-date=7 November 2009 |archive-url=https://web.archive.org/web/20091107044928/http://www.radio-club-of-america.org/history.php?page=1921.html |url-status=live}}</ref>

<ref name=RijksOverheid2007>{{cite web |url=http://www.rijksoverheid.nl/onderwerpen/frequentiebeleid/documenten-en-publicaties/rapporten/2007/01/18/nationaal-frequentieplan-nfp.html |title=Nationaal Frequentieplan |website=rijksoverheid.nl |access-date=6 March 2014 |archive-date=6 March 2014 |archive-url=https://web.archive.org/web/20140306192219/http://www.rijksoverheid.nl/onderwerpen/frequentiebeleid/documenten-en-publicaties/rapporten/2007/01/18/nationaal-frequentieplan-nfp.html |url-status=live}}</ref>

<ref name=RohdeWhitaker2000>{{cite book |last1=Rohde |first1=Ulrich L. |last2=Whitaker |first2=Jerry |title=Communications Receivers: DSP, software radios, and design |edition=third |date=6 December 2000 |publisher=McGraw Hill Professional |place=New York, NY |isbn=0-07-136121-9}} {{ISBN|978-007-136121-7}}</ref>

<ref name=Sheppard2009>{{cite book |last=Sheppard |first=David |title=On Some Faraway Beach: The life and times of Brian Eno |url=https://books.google.com/books?id=rZluAAAAQBAJ&pg=PA275 |date=1 May 2009 |publisher=Chicago Review Press |isbn=978-1-55652-107-2 |pages=275 ff |access-date=15 February 2018 |archive-date=25 January 2022 |archive-url=https://web.archive.org/web/20220125091408/https://books.google.com/books?id=rZluAAAAQBAJ&pg=PA275 |url-status=live}}</ref><ref name=Wire2000>{{cite book |title=The Wire |url=https://books.google.com/books?id=zB5MAAAAYAAJ |year=2000 |publisher=C. Parker |access-date=15 February 2018 |archive-date=20 August 2020 |archive-url=https://web.archive.org/web/20200820040107/https://books.google.com/books?id=zB5MAAAAYAAJ |url-status=live}}</ref>

<ref name=Sinclair2000>{{cite book |last=Sinclair |first=Ian Robertson |title=Audio and Hi-Fi Handbook |publisher=Newnes |year=2000 |isbn=0-7506-4975-5 |pages=195–196}}</ref>

<ref name=Sterling2004>{{cite book |last=Sterling |first=Christopher H. |title=Encyclopedia of Radio |url=https://books.google.com/books?id=-UeveLMilioC&pg=PA538 |date=March 2004 |publisher=Routledge |isbn=978-1-135-45649-8 |pages=538 ff |access-date=28 November 2017 |archive-date=19 August 2020 |archive-url=https://web.archive.org/web/20200819235533/https://books.google.com/books?id=-UeveLMilioC&pg=PA538 |url-status=live}}</ref>

<ref name=SWRad_GS400>{{cite web |url=http://www.shortwaveradio.ch/radio-e/grundig-sat400-e.htm |title=Grundig Satellit&nbsp;400 international / professional |website=ShortWaveRadio.ch |access-date=16 February 2018 |archive-date=13 February 2018 |archive-url=https://web.archive.org/web/20180213181817/http://www.shortwaveradio.ch/radio-e/grundig-sat400-e.htm |url-status=live}}</ref>

<ref name=SWRad_Panasonic>{{cite web |url=http://www.shortwaveradio.ch/radio-e/panasonic-e.htm |title=Panasonic / National |website=ShortwaveRadio.ch |access-date=16 February 2018 |archive-date=12 February 2018 |archive-url=https://web.archive.org/web/20180212140047/http://www.shortwaveradio.ch/radio-e/panasonic-e.htm |url-status=live}}</ref>

<ref name=thethe2011>{{cite web |url=http://www.thethe.com/sections/radio.php |title=Radio Cineola |website=thethe.com |archive-url=https://web.archive.org/web/20111218173001/http://www.thethe.com/sections/radio.php |archive-date=18 December 2011 |df=dmy-all}}</ref>

<ref name=ThirdNRC_1924>{{cite book |url=https://babel.hathitrust.org/cgi/pt?id=pst.000015526212;view=1up;seq=17 |title=Frequency or wave band allocations |series=Recommendations for Regulation of Radio Adopted by the Third National Radio Conference |date=6–10 October 1924 |page=15 |access-date=14 April 2019 |archive-date=8 March 2021 |archive-url=https://web.archive.org/web/20210308103922/https://babel.hathitrust.org/cgi/pt?id=pst.000015526212;view=1up;seq=17 |url-status=live}}</ref>

<ref name=w4uvh>{{cite web |url=http://www.w4uvh.net/dxld7078.txt |website=w4uvh.net |title=dxld7078 |access-date=2009-10-21 |archive-date=9 April 2010 |archive-url=https://web.archive.org/web/20100409092638/http://www.w4uvh.net/dxld7078.txt |url-status=live}}</ref>

<ref name=Wörner1973>{{cite book |first=Karl Heinrich |last=Wörner |title=Stockhausen: Life and work |url=https://books.google.com/books?id=aqmMPnlXZOMC&pg=PA76 |year=1973 |publisher=University of California Press |isbn=978-0-520-02143-3 |pages=76 ff |access-date=15 February 2018 |archive-date=18 August 2020 |archive-url=https://web.archive.org/web/20200818220820/https://books.google.com/books?id=aqmMPnlXZOMC&pg=PA76 |url-status=live}}</ref>

<ref name=BBC2022>{{cite web |url=https://www.bbc.co.uk/mediacentre/2022/millions-of-russians-turn-to-bbc-news |title=Millions of Russians turn to BBC News |publisher=BBC |access-date=4 March 2022 |archive-date=4 March 2022 |archive-url=https://web.archive.org/web/20220304051945/https://www.theguardian.com/media/2022/mar/04/bbc-website-blocked-in-russia-as-shortwave-radio-brought-back-to-cover-ukraine-war |url-status=live}}</ref>
}}

== External links ==
* {{cite web |url=http://www.swling.com/ |website=SWLing.com |title=A beginner's guide to shortwave radio listening}}
* {{cite web |url=https://www.qsl.net/4x4xm/HF-Propagation.htm |title=Understanding HF Skywave Propagation}}
* {{cite web |url=http://worldofradio.com |first=Glenn |last=Hauser |title=World of Radio}}
* {{cite web |url=http://propagation.hfradio.org/ |title=Space Weather and Radio Propagation Center |website=propagation.hfradio.org}} View live and historical data and images of [[Astronomy:Space weather|space weather]] and [[Physics:Radio propagation|radio propagation]].
* {{cite magazine |url=http://www.economist.com/world/international/displaystory.cfm?story_id=11590746&fsrc=RSS |title=Short-wave radio, snap and crackle goes pop. Life in the old wireless yet |magazine=[[Finance:The Economist|The Economist]]}} article describing pros and cons of short wave radio since the [[History:Cold War|Cold War]].
* {{cite news |url=https://books.google.com/books?id=4OIDAAAAMBAJ&q=Popular+Science+1930+plane+%22Popular+Mechanics%22&pg=-PA114 |title=Short-wave radio telephone is success in tests |magazine=Popular Mechanics |date=July 1931 |publisher=Hearst Magazines |at=mid page 114}} describes experiments carried out for the French and British governments.

{{TimeSig}}
{{Audio broadcasting}}
{{radio spectrum}}
{{EMSpectrum}}
{{Telecommunications}}
{{Radio listening}}

[[Category:Radio spectrum]]

{{Sourceattribution|Shortwave radio}}