Encyclopedia
Shortwave radio operates between the
frequencies of 2,310 kHz and 30 MHz 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 those commonly 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.
High-frequency propagation
Shortwave frequencies are capable of reaching the other side of the planet because they can be refracted by the
ionosphere . 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 can travel longer distances than lower ones; at night, this property is reversed.
The dependence to the time of the day is due to a particular transient atmosphere ionized layer forming only during day when atoms are broken up into ions by sun photons. This layer is responsible for partial or total absorption of particular frequences.
- 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: 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, digital, or other systems, which require software or 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
- 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
The Asia-Pacific Telecommunity estimates that there are approximately 600,000,000 shortwave radio receivers in use in 2002.
ITU frequency allocation
The World Radiocommunication Conference , 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 in 1997, the following bands were allocated to international broadcasters :
| 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, 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 | |
| 41 m | 7,100 - 7,300 kHz | not in the Americas, shared with the amateur radio 40 meter band |
| 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 | |
Analog AM 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 can currently be modeled by
Ioncap is propagation prediction software is available for free from the U.S. Department of Commerce Institute for Telecommunication Sciences [High Frequency Propagation Models].
VOACAP, an improved version of IONCAP, is a free professional HF propagation prediction program from NTIA/ITS, originally developed for Voice of America .
- 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 .
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
Software
User guides
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 two way communications 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 .
In Canada, this licensing agency is
Industry Canada.
In February 1990, the FCC removed the
morse code proficiency requirement for the Technician class amateur radio license, which allows one to transmit on frequencies above 30 MHz. Technician licensees who passed a 5 word per minute morse code test were allowed limited HF privileges, similar to those of Novice licensees. This has made it easier for beginners to get involved in the hobby; 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. It should be noted that many amateur radio operators started out as Shortwave Listeners and actively encourage SWLs to become amateur radio operators.
The 2003 World Administrative Radio Conference 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 . 20 countries 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 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. 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. It is not clear when the FCC will act on this, if at all.
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 '; 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 . Some even listen to two way communications by amateur radio operators. 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. Alternatively, many international broadcasters 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.
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 , also known as Broadband over Power Lines , 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 ,
Hymnen and
Spiral .
Holger Czukay, John Duncan, Orchestral Manoeuvres in the Dark ,
Pat Metheny,
Aphex Twin,
Boards of Canada, Rush,
Able Tasmans, Meat Beat Manifesto, Daybrokenroses, Jonny Greenwood of
Radiohead, and
Wilco have also used or been inspired by broadcasts.
See also
External links and references
;Citations
;Other
-
-
-
- ¨The SWDXER¨ - with general SWL information and radio antenna tips.
- A history of Shortwave Radio Broadcasting in the 1920s
- minute by minute broadcast schedules and more
- multilingual dx news
- W1AW Code Practice Files
- Weekly audio and archive updates "Glenn Hauser's World of Radio"
