Shortwave
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High-frequency propagation
Shortwave frequencies are capable of reaching the other side of the planet 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, higher shortwave frequencies (> 10 MHz) can travel longer distances than lower ones; at night, this property is reversed.
- Season of the year.
- Solar conditions, including the number of sunspots, solar flares, and overall solar activity. Solar flares can prevent the ionosphere from reflecting or refracting radio waves.
- Type of modulation. Independent from the frequency, the receiver must be capable to receive the same modulation type of the transmitter
Modulation formats used
Types of modulation frequently used in the shortwave frequency range are:- AM: amplitude modulation. Usually used for shortwave broadcasting, and some aeronautical communications.
- NFM: Narrow-band frequency modulation. Normally used for VHF communication, but some NFM transmissions occur in the higher HF frequencies.
- SSB: Single sideband(USB/LSB): This is used for long-range communications by ships and aircraft, for voice transmissions by amateur radio operators, and for broadcasting.
- CW: Continuous/Carrier wave, which is used for Morse code communications.
- DRM: Digital Radio Mondiale: digital modulation for use on bands below 30 MHz.
- Various radioteletype, fax, or other systems, which require special equipment to decode.
User base
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 (which explains why shortwave is also known as "world band radio")
- 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
- Numbers stations
- Amateur radio operators
- Time signal stations
ITU frequency allocation
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 the World Administrative Radio Conference (WARC) in 1997, the following bands were allocated to international broadcasters (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 | not in the Americas |
| 60 m | 4,750 - 5,060 kHz | tropic band |
| 49 m | 5,900 - 6,200 kHz | |
| 41 m | 7,100 - 7,300 kHz | not in the Americas |
| 41 m | 7,300 - 7,350 kHz | |
| 31 m | 9,400 - 9,900 kHz | |
| 25 m | 11,600 - 12,100 kHz | |
| 22 m | 13,570 - 13,870 kHz | |
| 19 m | 15,100 - 15,800 kHz | |
| 16 m | 17,480 - 17,900 kHz | |
| 15 m | 18,900 - 19,020 kHz | |
| 13 m | 21,450 - 21,850 kHz | |
| 11 m | 25,600 - 26,100 kHz |
Shortwave broadcasting channels are allocated with a 5 kHz separation.
International broadcasters, however, may operate outside the normal WARC-allocated bands or use off-channel frequencies to attract attention in crowded bands. The new digital audio broadcasting format for shortwave DRM operates in 5khz, 10khz or 20 khz channels -- so there are some ongoing discussions with respect to specific band allocation for DRM.
The power used by shortwave transmitters ranges from less than one watt for some experimental transmissions to 500 kilowatts and higher for intercontinental broadcasters. Shortwave transmitting centers often use specialized antenna designs to concentrate radio energy on a bearing aimed at the target area.
Shortwave propagation
Shortwave propagation software can be modeled by:
- Ioncap (for point to point calculations)
- VOACAP (for area coverage calcuations)
VOACAP, an improved version of IONCAP, is a free professional HF propagation prediction program from NTIA/ITS, originally developed for Voice of America (VOA). VOACAP retains all of the theory as put forth by John Lloyd, George Haydon, Donald Lucas and Larry Teters in the 1975–1985 time-frame.
Major improvements in the IONCAP program were made by Franklin Rhoads of the U.S. Navy Research Laboratory under the sponsorship of the Voice of America (1985–1996).
Many of the newer features in VOACAP and VOAAREA were designed and implemented by Gregory Hand at the Institute for Telecommunication Sciences who created VOAAREA.
- VOACAP is the result of 50+ years HF research and development
- VOACAP is considered to be the most professional HF system performance prediction tool
- VOACAP is currently used for HF frequency planning by Voice of America and a number of other international HF broadcasters
User guides: http://www.voacap.com/
International broadcasting
See International broadcasting for details on the history and practice of broadcasting to foreign audiences.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 purposes known as amateur radio, is granted through a licensing process by the authorized ITU government body. In the USA, this licensing agency is the Federal Communications Commission (FCC). In Canada, this licensing agency is Industry Canada. Recently the FCC has added an amateur radio license which requires no knowledge of Morse code, making it easier for beginners to get involved; however, a working knowledge of Morse code is required to operate on shortwave bands.Amateur radio operators have made numerous 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.
The 2003 World Administrative Radio Conference (WARC) 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). 20 countries (largely Western Europe, Canada & Australia) have phased out this requirement from their licenses and giving access to operators who previously couldn't operate in HF. On the other hand, this trend is not global. Over 200 countries (e.g. Russia, Eastern Europe, Middle East, Africa, South America & Asia) have decided to keep the Morse Code requirement for the foreseeable future. The Federal Communications Commission is considering removal of the Morse Code requirement for the United States, but a decision - if any - is not expected until late 2006 or 2007.
Shortwave listening
Many hobbyists listen to shortwave broadcasters without operating transmitters. In some cases, the goal is to obtain 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. Many though tune the shortwave bands for the programmes of stations broadcasting to a general audience (such as the Voice of America, BBC World Service, Radio Australia, etc.). Nowadays, as the Internet evolves, the hobbyist can listen to shortwave signals via remotely controlled shortwave receivers around the world, even without owning a shortwave radio. See for example http://www.dxtuners.comShortwave listeners, or SWLs, can obtain QSL cards from broadcasters or utility stations as trophies of the hobby.
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. From 1976 to 1989, the Russian Woodpecker blotted out countless shortwave broadcasts daily; at first it was thought to be a secret submarine communication system, but it was quickly found to be an early-warning over the horizon radar system.Shortwave's future
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 uprise 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.
Shortwave broadcasts and music
Some musicians have been attracted to the unique aural qualities of shortwave radio. John Cage employed shortwave radios as live instruments in a number of pieces, and other musicians have sampled broadcasts, used tape loops of broadcasts, or drawn inspiration from the unusual sounds on some frequencies. Karlheinz Stockhausen used shortwave radio in works including Telemusik (1966), Hymnen (1966-67) and Spiral (1968). Holger Czukay, John Duncan, Orchestral Manoeuvres in the Dark (on their Dazzle Ships album), Pat Metheny, Aphex Twin, Boards of Canada, Rush, Meat Beat Manifesto, Daybrokenroses, and Wilco have also used or been inspired by broadcasts.See also
- List of American shortwave broadcasters
- International broadcasting
- Amateur radio
- Shortwave bands
- ALLISS (Antennas used in International Broadcasting)
- HRS type antennas (Antennas used in International Broadcasting)
- Superrock KYOI
- [The Conet project] - Recordings of Shortwave Numbers Stations [ird059] (0)
External links and references
- Citations
- Other
- [Shortwave Listening Guide]
- [DXing.info]
- [Monitoring Monthly - Radio Listeners' Magazine]
- [SWL] ¨Greg's Radio Site¨ - with general SWL information and radio antenna tips.
- [Surfing the Aether] A history of Shortwave Radio Broadcasting in the 1920s
| Radio spectrum | ||||||||||
| ELF | SLF | ULF | VLF | LF | MF | HF | VHF | UHF | SHF | EHF |
| 3 Hz | 30 Hz | 300 Hz | 3 kHz | 30 kHz | 300 kHz | 3 MHz | 30 MHz | 300 MHz | 3 GHz | 30 GHz |
| 30 Hz | 300 Hz | 3 kHz | 30 kHz | 300 kHz | 3 MHz | 30 MHz | 300 MHz | 3 GHz | 30 GHz | 300 GHz |
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