Shortwave

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Image:Grundigsw.jpgShortwave radio operates between the frequencies of 3,000 kHz and 30 MHz (30,000 kHz) 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.

Short wavelengths are associated with high frequencies because there is an inverse relationship between frequency and wavelength.

Contents

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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. 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.

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
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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.
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User base

Some major users of the shortwave radio band include

The Asia-Pacific Telecommunity estimates that there are approximately 600,000,000 shortwave radio receivers in use in 2002.

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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.

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Shortwave propagation

Shortwave propagation software can be modeled by:

  • Ioncap (for point to point calculations)
  • VOACAP (for area coverage calcuations)

Ioncap is propagation prediction software is available for free from the U.S. Department of Commerce (NTIA/ITS) 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 (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

Software: http://elbert.its.bldrdoc.gov/hf.html

User guides: http://www.voacap.com/

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International broadcasting

See International broadcasting for details on the history and practice of broadcasting to foreign audiences.

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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.

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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.com

Shortwave listeners, or SWLs, can obtain "QSL" cards from broadcasters or utility stations as trophies of the hobby.

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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.

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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.

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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), and Holger Czukay. 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.

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See also

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External links


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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