Shortwave
From Wikipedia, the free encyclopedia
Shortwave radio operates between the frequencies of 3 MHz (3,000 kHz) and 30 MHz (30,000 kHz) [1] and came to be referred to as such in the early days of radio because the wavelengths associated with this frequency range were shorter than the long wave lengths widely in use at that time. An alternate name is HF or high frequency radio. Short wavelengths are associated with high frequencies because there is an inverse relationship between frequency and wavelength.
Contents |
[edit] Overview
[edit] Radio amateurs discover long distance shortwave propagation
 |
This article or section deals primarily with the United States and does not represent a worldwide view of the subject. Please improve this article or discuss the issue on the talk page. |
Amateur radio operators are usually credited with the discovery of long distance communication in the shortwave bands. The first successful transatlantic tests were conducted by radio amateurs in December 1921 operating in the 200 meter mediumwave band, the shortest wavelength then available to amateurs. In 1922 hundreds of North American amateurs were heard in Europe at 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 upper edge of the 150-200 meter band--the official wavelengths allocated to amateurs by the Second National Radio Conference in 1923--forced amateurs to shift to shorter and shorter wavelengths; however, amateurs were limited by regulation to wavelengths longer than 150 meters. A few fortunate amateurs who obtained special permission for experimental communications below 150 meters completed hundreds of long distance two way contacts on 100 meters in 1923 including the first transatlantic two way contacts in November 1923, on 110 meters.
By 1924 many additional specially licensed amateurs were routinely making transoceanic contacts at distances of 6000 miles and more. On September 21, several amateurs in California completed two way contacts with an amateur in New Zealand. On October 19th, amateurs in New Zealand and England completed a 90 minute two way contact nearly half way around the world. On October 10th, three shortwave bands were officially made available to amateurs by the Third National Radio Conference, at 80, 40 and 20 meters. The 10 meter band was created by the Washington International Radiotelegraph Conference on November 25, 1927. The 15 meter band was opened to amateurs in the United States on May 1, 1952.
[edit] Marconi takes the world by surprise
In June and July 1923, Guglielmo Marconi quietly completed successful night time transmissions on 97 meters from Poldhu Wireless Station, Cornwall to his yacht Elettra in the Cape Verde Islands. In September 1924, Marconi completed successful daytime and nighttime transmissions on 32 meters from Poldhu to his yacht in Beirut. Marconi took the world by surprise in July 1924 when he 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. The UK-to-Canada shortwave "Beam Wireless Service" went into commercial operation on 25 October, 1926. Beam Wireless Services from the UK to Australia, South Africa and India went into service in 1927.
Shortwave soon became an extremely disruptive technology. Far more spectrum is available for long distance communication in the shortwave bands than in the longwave bands; and shortwave transmitters, receivers and antennas were orders of magnitude less expensive than the multi-hundred kilowatt transmitters and monstrous antennas needed for longwave.
Shortwave communications began to grow exponentially in 1927[citation needed], similar to the internet in the late 20th century. By 1928, more than half of long distance communications had transitioned from transoceanic cables and longwave wireless services to shortwave and the overall volume of transoceanic shortwave communications had vastly increased. Shortwave also ended the need for multi-million dollar investments in new transoceanic telegraph cables and massive longwave wireless stations, although some existing transoceanic telegraph cables and commercial longwave communications stations remained in use until the 1960s.
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 [2] 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.
[edit] Shortwave propagation
Shortwave frequencies are capable of reaching any location on the Earth because they can be refracted by the ionosphere (a phenomenon known as Skywave propagation). The selection of a frequency to use to reach a target area depends on several factors:
- The distance from the transmitter to the target receiver.
- Time of day. During the day, frequencies higher than approximately 12 MHz can travel longer distances than lower ones; at night, this property is reversed. The dependence on the time of the day is due to a particular transient atmosphere ionized layer known as the D Layer, forming only during day when photons from the sun break up atoms into ions and free electrons. This layer is responsible for partial or total absorption of particular frequencies.
- Season. During the winter months the AM broadcast band tends to be more favorable because of longer hours of darkness.
- Solar activity. Sunspots, solar flares, and overall solar variation affect the ionosphere. Solar flares can prevent the ionosphere from reflecting or refracting radio waves.
[edit] Types of Modulation
- Further information: Modulation
Independent from frequency, the receiver must also be capable of receiving the modulation type being transmitted. AM, Singlesideband and CW are common modulations. Types of modulation frequently used in the shortwave frequency range are:
- AM: amplitude modulation. Most commonly used for shortwave broadcasting.
- SSB: Single sideband: This is used for long-range communications by ships and aircraft, for voice transmissions by amateur radio operators, and for broadcasting. LSB (lower sideband) is generally used below 9 MHz and USB (upper sideband) above 9 MHz.
- CW: Continuous wave, which is used for Morse code communications.
- NBFM: Narrow-band frequency modulation. Primarily military NFM transmissions occur in the higher HF frequencies (typically above 20 MHz). Because of the larger bandwidth required, NBFM is much more commonly used for VHF communication. NBFM is poorly suited for long range SW broadcasting due to the multiphasic distortions created by the ionosphere.
- DRM: Digital Radio Mondiale: digital modulation for use on bands below 30 MHz.
- Various radioteletype, fax, digital, slow-scan television--or other systems, which require software or special equipment to decode.
[edit] Users
Some major users of the shortwave radio band include:
- Domestic broadcasting in countries with a widely dispersed population with few longwave, mediumwave, or FM stations serving them;
- International broadcasting to foreign audiences (also known as "world band radio");
- Speciality political, religious, and conspiracy theory radio networks, individual commercial and non-commercial paid broadcasts for the North American and other markets;
- Utility stations transmitting messages not intended for a general public, such as aircraft flying between continents, encoded or ciphered diplomatic messages, weather reporting, or ships at sea;
- Clandestine stations. These are stations that initiate broadcasts on behalf of various political movements, including rebel or insurrectionist forces, and are normally unauthorized by the government-in-charge of the country in question. Clandestine broadcasts may emanate from transmitters located in rebel-controlled territory or from outside the country entirely, using another country's transmission facilities;
- Numbers Stations Officially these stations do not exist as they are unlicensed and untraceable yet regularly appear and disappear all over the shortwave radio band range. It is believed that Numbers Stations are operated by government agencies and are used by these agencies to communicate with clandestine operatives working within foreign countries however, no definitive proof of such use has emerged. As the vast majority of these broadcasts contain nothing but the recitation of blocks of numbers, in various languages, with the occasional 'burst' of music, they have become known as 'Number Stations', although they actually lack any official designation. Perhaps the most famous example of a Number Station is the Lincolnshire Poacher (numbers station) named after the 18 cent. English folk song, which is broadcast just prior to the recitation of the number sequences.;
- Amateur radio operators;
- Time signal stations: In North America, WWVand WWVH operate on these frequencies: 2500 kHz, 5000 kHz, 10000 kHz, 15000 kHz, and 20000 kHz. CHU Canada operates on these frequencies: 3335 kHz, 7335 kHz, and 14670 kHz. Other similar stations operate on various shortwave and longwave frequencies throughout the world;
- Over-the-horizon radar From 1976 to 1989, the Russian Woodpecker over the horizon radar system blotted out countless shortwave broadcasts daily.
The term DXing, in the context of listening to radio signals of any user of the shortwave band, is the activity of monitoring distant stations. In the context of amateur radio operators, the term 'DXing' refers to the two-way communications with a distant station, using shortwave radio frequencies.
The Asia-Pacific Telecommunity estimates that there are approximately 600,000,000 shortwave broadcast radio receivers in use in 2002.[citation needed][dubious ] WWCR claims that there are 1.5 billion shortwave receivers worldwide.[3]
[edit] Shortwave broadcasting 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 next WRC is scheduled to take place in 2007.
At WRC-97 in 1997, the following bands were allocated for international broadcasting. (listed in the table):
| Meter Band | Frequency Range | Remarks |
|---|---|---|
| 120 m | 2,300 - 2,495 kHz | tropic band |
| 90 m | 3,200 - 3,400 kHz | tropic band |
| 75 m | 3,900 - 4,000 kHz | shared with the amateur radio 75/80 meter band |
| 60 m | 4,750 - 5,060 kHz | tropic band |
| 49 m | 5,900 - 6,200 kHz | |
| 40 m/41m | 7,100 - 7,350 kHz | shared with the amateur radio 40 meter band |
| 31 m | 9,400 - 9,900 kHz | Currently most heavily used band |
| 25 m | 11,600 - 12,100 kHz | |
| 22 m | 13,570 - 13,870 kHz | substantially used only in Eurasia |
| 19 m | 15,100 - 15,800 kHz | |
| 16 m | 17,480 - 17,900 kHz | |
| 15 m | 18,900 - 19,020 kHz | almost unused, could become a DRM band |
| 13 m | 21,450 - 21,850 kHz | |
| 11 m | 25,600 - 26,100 kHz | may be used for local DRM broadcasting |
AM shortwave broadcasting channels are allocated with a 5 kHz separation for traditional analog audio broadcasting.
International broadcasters for practical reasons sometimes operate outside the normal WRC-allocated bands or use off-channel frequencies 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.
[edit] Shortwave broadcasting
There are two aspects of shortwave broadcasting
Shortwave does possess a number of advantages over newer technologies, including the following:
- The difficulty in censoring programming by authorities in target countries: unlike the Internet, government authorities cannot monitor which stations (sites) are being listened to (accessed). For example, during the coup against President Mikhail Gorbachev, when his access to communications was limited, Gorbachev was able to stay informed by means of the BBC World Service on shortwave.[citation needed]
- Low-cost shortwave radios are widely available in all but the most repressive countries in the world.
- In many countries (particularly in most third world nations and in the Eastern bloc during the Cold War era) ownership of shortwave receivers is widespread[citation needed] (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 for a short time.
- Shortwave radios can be used in situations where Internet or satellite technology is unavailable (or unaffordable).
- Shortwave radio travels much farther than FM. Shortwave broadcasts can be heard from all parts of the world, in all parts of the world.
These benefits are widely regarded as being outweighed by the drawbacks such as these:
- Shortwave broadcasts often suffer from serious interference problems because of overcrowding on the wavebands, atmospheric disturbances and electrical interference problems (particularly in cities) from TV sets, computers, poorly designed domestic appliances, and substandard electrical installations.
- Even under ideal reception conditions, the audio quality of a shortwave broadcast is usually inferior to that of domestic stations, particularly FM stations
- As more people around the world have access to television and the Internet, old technologies such as shortwave radio find it difficult to compete for listeners' attention.
- In most Western countries, ownership of shortwave radios is limited to interested enthusiasts. Therefore, audiences are limited.
- The dependence of shortwave radio on atmospheric conditions (the best frequency for hearing certain parts of the world varies by time of day and season) means that it can be difficult to use by non-technically minded listeners.
- 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.
[edit] Amateur radio
In the U.S. and Canada, no license is required to own or operate a shortwave receiver. The privilege of operating a shortwave radio transmitter for non-commercial two way communications known as amateur radio is granted through a licensing process by authorized government agencies.
In the USA, the licensing agency is the Federal Communications Commission (FCC). In Canada, the licensing agency is Industry Canada. As of February 2007, the FCC eliminated the Morse code requirement for all Amateur Radio operator classes, thereby allowing more operators to transmit in the HF bands.
Amateur radio operators have made many technical advancements in the field of radio and make themselves available to transmit emergency communications when normal communications channels fail. Some amateurs practice operating off the power grid so as to be prepared for power loss. It should be noted that many amateur radio operators started out as Shortwave Listeners (SWLs) and actively encourage SWLs to become amateur radio operators.
The 2003 World Radiocommunication Conference (WRC) removed the global requirement for Morse code proficiency needed to access most shortwave frequencies for the amateur radio service, but left the decision to each administrative body (e.g. Federal Communications Commission in the United States; Industry Canada in Canada). Many countries have phased out this requirement from their licenses and give access to the shortwave frequencies to all licencees. A few countries however have decided to keep the Morse Code requirement for the foreseeable future. In July 2005, the Federal Communications Commission recommended the removal of the Morse code requirement for amateur radio licenses the United States, as part of a Notice of Proposed Rulemaking in WT Docket 05-235.[4] This docket was released after 18 proposals, including one from the ARRL for widespread changes in the Amateur Radio Service rules were received and considered by the FCC. These proposals had attracted 6200 comments from the Amateur Radio Service community. The FCC released a Report and Order on December 19, 2006, eliminating the Morse code requirement for amateur radio licensing in the United States.
[edit] Shortwave listening
- Further information: Shortwave listening
Many hobbyists listen to shortwave broadcasters without operating transmitters. 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, or the two way communications by amateur radio operators.
Many listeners tune the shortwave bands for the programmes of stations broadcasting to a general audience (such as Radio Canada International, Voice of America, BBC World Service, Radio Australia,Radio Netherlands, etc.). Today, through the evolution of the Internet, the hobbyist can listen to shortwave signals via remotely controlled shortwave receivers around the world, even without owning a shortwave radio. Many international broadcasters (such as Radio Canada International [2], the BBC and Radio Australia) offer live streaming audio on their websites.
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.
[edit] Utility stations
Utility stations are stations that do not broadcast to the general public. There are shortwave bands allocated to the use of 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. Many radio hobbyists specialize in listening to "ute" broadcasts, which often come from places without shortwave broadcasters.
[edit] Unusual signals
Numbers stations are shortwave radio stations of uncertain origin that broadcast streams of numbers, words, or phonetic sounds. Although officially there is no indication of their origin, radio hobbyists have determined that many of them are used by intelligence services as one-way communication to agents in other countries. For other examples, see The Conet Project.
[edit] Shortwave's future
- Further information: The future of shortwave listening
The development of direct broadcasts from satellites has reduced the demand for shortwave receivers, but there are still a great number of shortwave broadcasters. A new digital radio technology, Digital Radio Mondiale, is expected to improve the quality of shortwave audio from very poor to standards comparable to the FM broadcast band. The future of shortwave radio is threatened by the rise of power line communication (PLC), also known as Broadband over Power Lines (BPL), where a data stream is transmitted over unshielded power lines. As the frequencies used overlap with shortwave bands, severe distortions make listening to shortwave radio near power lines difficult or impossible. However, because it is a cheap and effective way to receive communications in countries with poor infrastructure, shortwave will be around for years to come.
[edit] Shortwave broadcasts and music
Some musicians have been attracted to the unique aural qualities of shortwave radio, employing shortwave radios as live instruments in a number of pieces, and or using sampled broadcasts, used tape loops of broadcasts, or drawn inspiration from the unusual sounds on some frequencies.
John Cage used radios live on several occasions, while Karlheinz Stockhausen used shortwave radio in works including Hymnen (1966–67), Kurzwellen (1968), Spiral (1968), and Michaelion (1997). Holger Czukay, a student of Stockhausen, was one of the first to use shortwave in a rock music context. In 1975, German electronic music band Kraftwerk recorded a full length concept album around simulated radiowave and shortwave sounds, entitled Radio-Activity.
Among others, Tom Robinson, Peter Gabriel, Pukka Orchestra, AMM, John Duncan, Orchestral Manoeuvres in the Dark (on their Dazzle Ships album), Pat Metheny, Aphex Twin, Boards of Canada, Rush, Able Tasmans, Team Sleep, Meat Beat Manifesto, Tim Hecker, Jonny Greenwood of Radiohead, and Wilco have also used or been inspired by shortwave broadcasts.
[edit] See also
Related topics
- ALLISS -- a very large rotatable antenna system used in International Broadcasting
- Amateur radio also uses the shortwave bands, but with power levels under 2kw
- HRS type antennas antennas most commonly used in International Broadcasting
- International broadcasting
- Shortwave bands shortwave's spectrum allocation
- shortwave relay station the fundamental way in which programmes are broadcast on shortwave
- PLL -- Phase Lock Loop, a feedback circuit used in most SW recivers
- SSB
Related organizations or broacasters
- List of American shortwave broadcasters
- Radio Nikkei, a Japanese domestic commercial shortwave station
- Superrock KYOI
[edit] References
- ^ Tomislav Stimac, "Definition of frequency bands (VLF, ELF... etc.)". IK1QFK Home Page (vlf.it).
- ^ Cable and Wireless — A history
- ^ 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 [1] WWCR FAQ
- ^ "FCC Proposes to Drop Morse Code Requirement for All License Classes", American Radio Relay League, Inc., July 20, 2005. Retrieved on 2006-08-03. (English)
[edit] External links
- Global Frequency Database
- SWLing ¨SWLing.com¨ - a simple and free beginner's guide to Shortwave Listening (SWLing). Designed to educate you and your family about SWLing.
- Shortwave Listening Guide
- Glenn Hauser's World of Radio website
- VOA: First on the Internet
- The Conet project - Recordings of Shortwave Numbers Stations [ird059] (0)
- Up-to-the-minute International Broadcast Schedules in English - this is a fast, general listing that draws from HFCC database and other sources.
- Space Weather and Radio Propagation Center View live and historical data and images of space weather and radio propagation.
- W1AW Code Practice Files
- The British DX Club
- The Listening Post An on-line shortwave radio you can tune and hear
- 30,000 Kilohertz of Sound Theatrical production that incorporates shortwave broadcasts.
The following external link is designed for use by cell phones and mobile devices that can display content using Wireless Markup Language and the Wireless Application Protocol:
- WAP/WML SWL Resources Search database of International Shortwave Broadcasting Stations by frequency, view Space weather and radio propagation data and images, and more.
|
||||||||||||||
|
||||||||||||||||||||||||||||||||||||||
|
|||||
