thumb|right|[[Grundig Satellit 400 solid-state, digital shortwave receiver, c. 1986 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
thumb|right|Radio amateurs carried out the first shortwave transmissions over a long distance before those of [[Guglielmo Marconi.]]
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 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 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. Franklin went on to refine the directional transmission by inventing the curtain array aerial system. 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, For example, two way shortwave communication is still used in remote regions by the Royal Flying Doctor Service of Australia.
- "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–meter bands. Licenses are granted by authorized government agencies.
- Time signal and radio clock stations: In North America, WWV radio and WWVH radio transmit at these frequencies: 2.5 MHz, 5 MHz, 10 MHz, and 15 MHz; and WWV also transmits on 20 MHz. The CHU radio station in Canada transmits on the following frequencies: 3.33 MHz, 7.85 MHz, and 14.67 MHz. Other similar 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.
- Over-the-horizon radar: From 1976 to 1989, the Soviet Union's Russian Woodpecker over-the-horizon radar system blotted out numerous shortwave broadcasts daily.
- Ionospheric heaters used for scientific experimentation such as the High Frequency Active Auroral Research Program in Alaska, and the Sura ionospheric heating facility in Russia. Concerns about the reliability, capacity, security and contagion risk presented by this use of shortwave technology have been raised.
Shortwave broadcasting<span class="anchor" id="shortwave_broadcasting_anchor"></span>
thumb|Transmitter room of shortwave station [[Yle in Pori, Finland, in 1954]]
- See 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 Shortwave relay station for the actual kinds of integrated technologies used to bring high power signals to listeners.
Frequency allocations
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 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:
{| 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 m
| 2.3–2.495 MHz
| tropical band
|- style="background:#e8e8e8;"
|| 90 m
|| 3.2–3.4 MHz
|| tropical band
|-
| 75 m
| 3.9–4 MHz
| shared with the North American ITU Region 2 amateur radio 80m band (3.5-4.0 MHz)
|- style="background:#e8e8e8;"
|| 60 m
|| 4.75–5.06 MHz
|| tropical band
|-
| 49 m
| 5.9–6.2 MHz
|
|- style="background:#e8e8e8;"
|| 41 m
|| 7.2–7.6 MHz
|| partly shared with the ITU Region 2 amateur radio 40m band (7.0-7.3 MHz)
|-
| 31 m
| 9.4–9.9 MHz
| the most heavily used band
|- style="background:#e8e8e8;"
|| 25 m
|| 11.6–12.2 MHz
||
|-
| 22 m
| 13.57–13.87 MHz
|
|- style="background:#e8e8e8;"
|| 19 m
|| 15.1–15.8 MHz
||
|-
| 16 m
| 17.48–17.9 MHz
|
|- style="background:#e8e8e8;"
|| 15 m
|| 18.9–19.02 MHz
|| almost unused, could become a DRM band
|-
| 13 m
| 21.45–21.85 MHz
|
|- style="background:#e8e8e8;"
|| 11 m
|| 25.6–26.1 MHz
|| may be used for local DRM broadcasting
|}
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, 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
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. 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.
In 2018, Nigel Fry, head of Distribution for the BBC World Service Group,