Amateur radio history
The birth of amateur radio, and radio in general, was associated with various amateur experimenters. Throughout its history, amateur radio enthusiasts have made significant contributions to science, engineering, industry, and social services. Research by amateur radio operators has founded new industries, built economies, empowered nations, and saved lives in times of emergency. The international symbol for amateur radio, included in the logos of many IARU member societies. The diamond holds a circuit diagram featuring components common to every radio: an antenna, inductor and ground.
[edit]Activities and practices
Radio amateurs use various modes of transmission to communicate. Voice transmissions are most common, with some such as frequency modulation (FM) offering high quality audio, and others such as single sideband (SSB) offering more reliable communications when signals are marginal and bandwidth is restricted.
Radiotelegraphy using Morse code remains popular, particularly on the shortwave bands and for experimental work, with its inherent signal-to-noise ratio advantages. Morse, using internationally agreed code groups, also facilitates communications between amateurs who speak different languages.[2] It is also popular with homebrewers as CW-only transmitters are simpler to construct. For many years demonstrating a proficiency in morse code was a requirement to obtain amateur licenses for the high frequency bands but following changes in international regulations in 2003 many countries have now dropped this requirement (the United States Federal Communications Commission did so in 2007). An amateur radio operator
Modern personal computers have led to a boom in digital modes such as radioteletype, which previously required cumbersome mechanical equipment.[3] Hams led the development of packet radio, which has since been augmented by more specialized modes such as PSK31 to facilitate real-time, low-power communications on the shortwave bands. Echolink using Voice over IP technology has enabled amateurs to communicate through local internet-connected repeaters via IRLP. Other modes, such as WSJT, are used for weak signal modes including meteor scatter and moonbounce communications.
Similarly, fast scan amateur television, once considered rather esoteric, has exploded in popularity thanks to cheap camcorders and video cards in home computers. Because of the wide bandwidth and stable signals required, amateur television is typically found in the 70 cm (420—450 MHz) frequency range, though limited usage also exists on 33 cm (902—928 MHz) and 23 cm (1240—1300 MHz). These requirements also effectively limit the signal range to between 20 and 60 miles (30—100 km), however, the use of linked repeater systems can allow transmissions across several states.[4]
These repeaters, or automated relay stations, are used on VHF and higher frequencies to increase signal range. Repeaters are usually located on top of a mountain, hill or tall building, and allow operators to communicate over hundreds of square miles using a low power hand-held transceiver. Repeaters can also be linked together by use of other amateur radio bands, landline or the Internet.
Communication satellites called OSCARs (Orbiting Satellite Carrying Amateur Radio) can be accessed, some using a handy-talkie (HT) with a stock "rubber duck" antenna. Hams also use natural satellites such as the moon and the ionized trails of meteors as reflectors of radio waves.[5] Hams are also often able to make contact with the International Space Station (ISS),[6] as many astronauts and cosmonauts are licensed as Amateur Radio Operators.[7]
Amateur radio operators use their amateur radio station to make contacts with individual hams as well as participating in round table discussion groups or "rag chew sessions" on the air. Some join in regularly scheduled on-air meetings with other amateur radio operators, called "Nets" (as in "networks") which are moderated by a station referred to as "Net Control".[8] Nets can allow operators to learn procedures for emergencies, be an informal round table or be topical, covering specific interests shared by a group.
[edit]LicensingMain article: Amateur radio license
In all countries, amateur radio operators are required to pass a licensing exam displaying knowledge and understanding of key concepts. This practice is in contrast to other unlicensed personal radio services such as CB radio, Multi-Use Radio Service, or Family Radio Service / PMR446 that are more heavily restricted. In return, hams are granted operating privileges in larger segments of the radio frequency spectrum using a wide variety of communication techniques with higher power levels permitted. A handheld VHF/UHF transceiver, 2007.
In many countries, amateur licensing is a routine civil administrative matter. Amateurs are required to pass an examination to demonstrate technical knowledge, operating competence and awareness of legal and regulatory requirements in order to avoid interference with other amateurs and other radio services. There are often a series of exams available, each progressively more challenging and granting more privileges in terms of frequency availability, power output, permitted experimentation, and in some countries, distinctive callsigns. Some countries such as Great Britain and Australia have begun requiring a practical training course in addition to the written exams in order to obtain a beginner's license. These beginner's licenses are referred to as Foundation Licenses.
Amateur radio licensing in the United States serves as an example of the way some countries award different levels of amateur radio licenses based on technical knowledge. Licensees previously needed to demonstrate proficiency in Morse Code, but these requirements were eliminated by the Federal Communications Commission on February 23, 2007.[9] This conforms with international law, which no longer mandates Morse code testing, as well as views by the FCC that Morse code should be treated like other communications techniques, and that written testing is sufficient to prove that an applicant is qualified to obtain an amateur radio license.[10] Some portions of the ham bands remain reserved for Morse code use only and the mode remains popular.Specialized Interests and modes
While many hams simply enjoy talking to friends, others pursue a wide variety of specialized interests.Emergency communications for community emergency response teamsHand building homebrew amateur radio gearDesigning new antennasCommunicating via amateur satellitesSevere weather spottingDX communication to far away countriesDX-peditionsUsing the Internet Radio Linking Project (IRLP) to connect radio repeaters via the InternetTracking vehicles using the Automatic Position Reporting System (APRS), which integrates with the GPSEngaging in the sport of contesting, earning awards, and collecting QSL cardsAmateur Radio Direction FindingHigh Speed TelegraphyLow-power operation (QRP).Vintage amateur radios, such as those using vacuum tube technologyHamfests, club meetings and swap meetsPortable, fixed, mobile and handheld operationVHF, UHF and microwave operation on amateur radio high bands
[edit]Newcomers
Many people have started in amateur radio by finding a local club. Clubs often provide information about licensing, local operating practices and technical advice. Newcomers also often study independently by purchasing books or other materials, sometimes with the help of a mentor, teacher or friend. In addition, many countries have national amateur radio societies which encourage newcomers and work with government communications regulation authorities for the benefit of all Amateurs. The oldest of these societies is the Wireless Institute of Australia, formed in 1910; other notable societies are the Radio Society of Great Britain, the American Radio Relay League, Radio Amateurs of Canada, the New Zealand Association of Radio Transmitters and South African Radio League. ( See Category:Amateur radio organizations)
[edit]Callsigns
After licensing, a radio amateur's national government issues a unique callsign to the radio amateur. The holder of a callsign uses it on the air to legally identify the operator or station during any and all radio communication.[11] In certain jurisdictions, once licensed, an operator may also select a "vanity" callsign for a fee.[12]
[edit]Privileges
In contrast to most commercial and personal radio services, radio amateurs are not restricted to using type-approved equipment, and radio amateurs may home-construct or modify equipment in any way so long as they meet spurious emission standards.
As noted, radio amateurs have access to frequency allocations throughout the RF spectrum, enabling choice of frequency to enable effective communication whether across a city, a region, a country, a continent or the whole world regardless of season or time day or night. The shortwave bands, or HF, can facilitate worldwide communication, the VHF and UHF bands offer excellent regional communication, and the broad microwave bands have enough space, or bandwidth, for television (known as SSTV and FSTV) transmissions and high-speed data networks.
Although allowable power levels are moderate by commercial standards, they are sufficient to enable global communication. Power limits vary from country to country; for example, the highest license classes are: 2.25 kilowatts in Canada, 2 kilowatts in most countries of the former Yugoslavia, 1.5 kilowatts in the United States, 1 kilowatt in Belgium and Switzerland, 750 watts in Germany, 500 watts in Italy, 400 watts in Australia and the United Kingdom and 150 watts in Oman. Lower license classes usually have lower power limits; for example, the lowest license class in the UK has a limit of just 10 watts. In the United States, licensed operators are allowed to use some 1,300 distinct modes of communications at effective radiated power levels ranging from microwatts to 1,500 watts.
When traveling abroad, the visiting ham must follow the rules of the country in which she or he wishes to operate. Some countries have reciprocal operating agreements to facilitate international operation, allowing hams from other countries to operate within their borders with just their home country license. Others require that a formal permit or new license be issued in advance.
[edit]Band plans and frequency allocationsMain article: Amateur radio frequency allocations
The International Telecommunication Union (ITU) governs the allocation of communications frequencies world-wide, with participation by each nation's communications regulation authority. National communications regulators have some liberty to restrict access to these frequencies or to award additional allocations as long as radio services in other countries do not suffer interference. In some countries, specific emission types are restricted to certain parts of the radio spectrum, and in most other countries, International Amateur Radio Union (IARU) member societies adopt voluntary plans to ensure the most effective use of spectrum.
In a few cases, a national telecommunication agency may also allow hams to use frequencies outside of the internationally allocated amateur radio bands. In Trinidad and Tobago, hams are allowed to use a repeater which is located on 148.80 MHz. This repeater is used and maintained by the National Emergency Management Agency (NEMA), but may be used by radio amateurs in times of emergency or during normal times to test their capability and conduct emergency drills. This repeater can also be used by non-ham NEMA staff and REACT members. In Alaska, U.S., amateur radio operators are allowed to use the statewide emergency frequency of 5165.7 kHz during an emergency.
Similarly, Amateurs in the United States may apply to be registered with the Military Affiliate Radio System (MARS). Once approved and trained, these amateurs also operate on US Government Military frequencies to provide contingency communications and morale message traffic support to the military services.
[edit]Popular cultureMain article: Amateur radio in popular culture
Amateur radio can be found throughout popular culture as a plot device. A classic example would be the "Radio Ham" episode of 1960s British comedy series "Hancock's Half Hour". A wealth of additional information may be found at the main article link shown above.
There are also famous Amateur radio operators such as King Juan Carlos I of Spain, radio and TV host Walter Cronkite, and Coast To Coast AM host Art Bell. Others include Gen. Curtis LeMay, Joe Walsh, Lance Bass, Barry Goldwater, Chet Atkins, Marlon Brando, King Hussein of Jordan, Patty Loveless, Ronnie Milsap, Bill "Bubba" Bussey from the nationally syndicated Rick and Bubba Show, Maine Governor John Baldacci, and Jean Shepherd, as well as most of the launched astronauts and cosmonauts.
[edit]ReferencesCited References^ Silver, H Ward (2004-04-23). Amateur Radio for Dummies. Indianapolis: Wiley Publishing. ISBN 0764559877. OCLC 55092631. ^ [1969] (2003) International Code of Signals. Bethesda, MD: National Imagery and Mapping Agency. Pub. 102. Retrieved on 2007-01-10. ^ Galbraith, E Art. "KH6BB and "Mighty Mo," the Battleship Missouri", ARRL.org, 2003-08-23. Retrieved on 2007-01-10. ^ Taggart, Ralph E (April 1993). "An Introduction to Amateur Television". QST via ARRL.org: 19—23. Retrieved on 2007-06-02. ^ Taylor, Joe. "WSJT: New Software for VHF Meteor-Scatter Communication", QST via ARRL.org, pp. 36—41. Retrieved on 2007-01-11. ^ ARISS: Amateur Radio on the International Space Station. ARRL.org. Retrieved on 2007-01-10.^ Jurrens, Gerald. Astronaut (and Former Astronaut) Hams. gjurrens at Tellurian.com. Retrieved on 2007-01-10.^ Haag, Jerry. Principles of Amateur Radio Net Control. SCC-AREA-RACES.org. Retrieved on 2007-01-10.^ FCC to Drop Morse Testing for All Amateur License Classes. ARRL.org (2006-12-19). Retrieved on 2007-05-16.^ FCC Report and Order 06-178A1 7. Federal Communications Commission (2006-12-19). Retrieved on 2007-05-16.^ Amateur Radio (Intermediate) Licence (A) or (B) Terms, Provisions and Limitations Booklet BR68/I. Ofcom.org.uk. Retrieved on 2007-06-02.^ Common Filing Task: Obtaining Vanity Call Sign. FCC.gov. Retrieved on 2007-06-02.General ReferencesStraw, R Dean (ed.) (October 2005). The ARRL Handbook for Radio Communications 2006, 83rd edition, Newington, CT: American Radio Relay League. ISBN 0-87259-949-3. OCLC 62026192. Bergquist, Carl J (2001-05-01). Ham Radio Operator's Guide, 2nd edition, Indianapolis: Prompt Publications. ISBN 0-7906-1238-0. OCLC 47051066. Dennison, Mike and Chris Lorek (eds.) (June 2005). Radio Communication Handbook, 8th edition, Potters Bar, Hertfordshire, England: Radio Society of Great Britain. ISBN 1-90508608-3. OCLC 123027893. Poole, Ian D (2001-10-31). HF Amateur Radio. Potters Bar, Hertfordshire, England: Radio Society of Great Britain. ISBN 1-872309-75-5. OCLC 47823876
The birth of amateur radio, and radio in general, was associated with various amateur experimenters. Throughout its history, amateur radio enthusiasts have made significant contributions to science, engineering, industry, and social services. Research by amateur radio operators has founded new industries, built economies, empowered nations, and saved lives in times of emergency. The international symbol for amateur radio, included in the logos of many IARU member societies. The diamond holds a circuit diagram featuring components common to every radio: an antenna, inductor and ground.
[edit]Activities and practices
Radio amateurs use various modes of transmission to communicate. Voice transmissions are most common, with some such as frequency modulation (FM) offering high quality audio, and others such as single sideband (SSB) offering more reliable communications when signals are marginal and bandwidth is restricted.
Radiotelegraphy using Morse code remains popular, particularly on the shortwave bands and for experimental work, with its inherent signal-to-noise ratio advantages. Morse, using internationally agreed code groups, also facilitates communications between amateurs who speak different languages.[2] It is also popular with homebrewers as CW-only transmitters are simpler to construct. For many years demonstrating a proficiency in morse code was a requirement to obtain amateur licenses for the high frequency bands but following changes in international regulations in 2003 many countries have now dropped this requirement (the United States Federal Communications Commission did so in 2007). An amateur radio operator
Modern personal computers have led to a boom in digital modes such as radioteletype, which previously required cumbersome mechanical equipment.[3] Hams led the development of packet radio, which has since been augmented by more specialized modes such as PSK31 to facilitate real-time, low-power communications on the shortwave bands. Echolink using Voice over IP technology has enabled amateurs to communicate through local internet-connected repeaters via IRLP. Other modes, such as WSJT, are used for weak signal modes including meteor scatter and moonbounce communications.
Similarly, fast scan amateur television, once considered rather esoteric, has exploded in popularity thanks to cheap camcorders and video cards in home computers. Because of the wide bandwidth and stable signals required, amateur television is typically found in the 70 cm (420—450 MHz) frequency range, though limited usage also exists on 33 cm (902—928 MHz) and 23 cm (1240—1300 MHz). These requirements also effectively limit the signal range to between 20 and 60 miles (30—100 km), however, the use of linked repeater systems can allow transmissions across several states.[4]
These repeaters, or automated relay stations, are used on VHF and higher frequencies to increase signal range. Repeaters are usually located on top of a mountain, hill or tall building, and allow operators to communicate over hundreds of square miles using a low power hand-held transceiver. Repeaters can also be linked together by use of other amateur radio bands, landline or the Internet.
Communication satellites called OSCARs (Orbiting Satellite Carrying Amateur Radio) can be accessed, some using a handy-talkie (HT) with a stock "rubber duck" antenna. Hams also use natural satellites such as the moon and the ionized trails of meteors as reflectors of radio waves.[5] Hams are also often able to make contact with the International Space Station (ISS),[6] as many astronauts and cosmonauts are licensed as Amateur Radio Operators.[7]
Amateur radio operators use their amateur radio station to make contacts with individual hams as well as participating in round table discussion groups or "rag chew sessions" on the air. Some join in regularly scheduled on-air meetings with other amateur radio operators, called "Nets" (as in "networks") which are moderated by a station referred to as "Net Control".[8] Nets can allow operators to learn procedures for emergencies, be an informal round table or be topical, covering specific interests shared by a group.
[edit]LicensingMain article: Amateur radio license
In all countries, amateur radio operators are required to pass a licensing exam displaying knowledge and understanding of key concepts. This practice is in contrast to other unlicensed personal radio services such as CB radio, Multi-Use Radio Service, or Family Radio Service / PMR446 that are more heavily restricted. In return, hams are granted operating privileges in larger segments of the radio frequency spectrum using a wide variety of communication techniques with higher power levels permitted. A handheld VHF/UHF transceiver, 2007.
In many countries, amateur licensing is a routine civil administrative matter. Amateurs are required to pass an examination to demonstrate technical knowledge, operating competence and awareness of legal and regulatory requirements in order to avoid interference with other amateurs and other radio services. There are often a series of exams available, each progressively more challenging and granting more privileges in terms of frequency availability, power output, permitted experimentation, and in some countries, distinctive callsigns. Some countries such as Great Britain and Australia have begun requiring a practical training course in addition to the written exams in order to obtain a beginner's license. These beginner's licenses are referred to as Foundation Licenses.
Amateur radio licensing in the United States serves as an example of the way some countries award different levels of amateur radio licenses based on technical knowledge. Licensees previously needed to demonstrate proficiency in Morse Code, but these requirements were eliminated by the Federal Communications Commission on February 23, 2007.[9] This conforms with international law, which no longer mandates Morse code testing, as well as views by the FCC that Morse code should be treated like other communications techniques, and that written testing is sufficient to prove that an applicant is qualified to obtain an amateur radio license.[10] Some portions of the ham bands remain reserved for Morse code use only and the mode remains popular.Specialized Interests and modes
While many hams simply enjoy talking to friends, others pursue a wide variety of specialized interests.Emergency communications for community emergency response teamsHand building homebrew amateur radio gearDesigning new antennasCommunicating via amateur satellitesSevere weather spottingDX communication to far away countriesDX-peditionsUsing the Internet Radio Linking Project (IRLP) to connect radio repeaters via the InternetTracking vehicles using the Automatic Position Reporting System (APRS), which integrates with the GPSEngaging in the sport of contesting, earning awards, and collecting QSL cardsAmateur Radio Direction FindingHigh Speed TelegraphyLow-power operation (QRP).Vintage amateur radios, such as those using vacuum tube technologyHamfests, club meetings and swap meetsPortable, fixed, mobile and handheld operationVHF, UHF and microwave operation on amateur radio high bands
[edit]Newcomers
Many people have started in amateur radio by finding a local club. Clubs often provide information about licensing, local operating practices and technical advice. Newcomers also often study independently by purchasing books or other materials, sometimes with the help of a mentor, teacher or friend. In addition, many countries have national amateur radio societies which encourage newcomers and work with government communications regulation authorities for the benefit of all Amateurs. The oldest of these societies is the Wireless Institute of Australia, formed in 1910; other notable societies are the Radio Society of Great Britain, the American Radio Relay League, Radio Amateurs of Canada, the New Zealand Association of Radio Transmitters and South African Radio League. ( See Category:Amateur radio organizations)
[edit]Callsigns
After licensing, a radio amateur's national government issues a unique callsign to the radio amateur. The holder of a callsign uses it on the air to legally identify the operator or station during any and all radio communication.[11] In certain jurisdictions, once licensed, an operator may also select a "vanity" callsign for a fee.[12]
[edit]Privileges
In contrast to most commercial and personal radio services, radio amateurs are not restricted to using type-approved equipment, and radio amateurs may home-construct or modify equipment in any way so long as they meet spurious emission standards.
As noted, radio amateurs have access to frequency allocations throughout the RF spectrum, enabling choice of frequency to enable effective communication whether across a city, a region, a country, a continent or the whole world regardless of season or time day or night. The shortwave bands, or HF, can facilitate worldwide communication, the VHF and UHF bands offer excellent regional communication, and the broad microwave bands have enough space, or bandwidth, for television (known as SSTV and FSTV) transmissions and high-speed data networks.
Although allowable power levels are moderate by commercial standards, they are sufficient to enable global communication. Power limits vary from country to country; for example, the highest license classes are: 2.25 kilowatts in Canada, 2 kilowatts in most countries of the former Yugoslavia, 1.5 kilowatts in the United States, 1 kilowatt in Belgium and Switzerland, 750 watts in Germany, 500 watts in Italy, 400 watts in Australia and the United Kingdom and 150 watts in Oman. Lower license classes usually have lower power limits; for example, the lowest license class in the UK has a limit of just 10 watts. In the United States, licensed operators are allowed to use some 1,300 distinct modes of communications at effective radiated power levels ranging from microwatts to 1,500 watts.
When traveling abroad, the visiting ham must follow the rules of the country in which she or he wishes to operate. Some countries have reciprocal operating agreements to facilitate international operation, allowing hams from other countries to operate within their borders with just their home country license. Others require that a formal permit or new license be issued in advance.
[edit]Band plans and frequency allocationsMain article: Amateur radio frequency allocations
The International Telecommunication Union (ITU) governs the allocation of communications frequencies world-wide, with participation by each nation's communications regulation authority. National communications regulators have some liberty to restrict access to these frequencies or to award additional allocations as long as radio services in other countries do not suffer interference. In some countries, specific emission types are restricted to certain parts of the radio spectrum, and in most other countries, International Amateur Radio Union (IARU) member societies adopt voluntary plans to ensure the most effective use of spectrum.
In a few cases, a national telecommunication agency may also allow hams to use frequencies outside of the internationally allocated amateur radio bands. In Trinidad and Tobago, hams are allowed to use a repeater which is located on 148.80 MHz. This repeater is used and maintained by the National Emergency Management Agency (NEMA), but may be used by radio amateurs in times of emergency or during normal times to test their capability and conduct emergency drills. This repeater can also be used by non-ham NEMA staff and REACT members. In Alaska, U.S., amateur radio operators are allowed to use the statewide emergency frequency of 5165.7 kHz during an emergency.
Similarly, Amateurs in the United States may apply to be registered with the Military Affiliate Radio System (MARS). Once approved and trained, these amateurs also operate on US Government Military frequencies to provide contingency communications and morale message traffic support to the military services.
[edit]Popular cultureMain article: Amateur radio in popular culture
Amateur radio can be found throughout popular culture as a plot device. A classic example would be the "Radio Ham" episode of 1960s British comedy series "Hancock's Half Hour". A wealth of additional information may be found at the main article link shown above.
There are also famous Amateur radio operators such as King Juan Carlos I of Spain, radio and TV host Walter Cronkite, and Coast To Coast AM host Art Bell. Others include Gen. Curtis LeMay, Joe Walsh, Lance Bass, Barry Goldwater, Chet Atkins, Marlon Brando, King Hussein of Jordan, Patty Loveless, Ronnie Milsap, Bill "Bubba" Bussey from the nationally syndicated Rick and Bubba Show, Maine Governor John Baldacci, and Jean Shepherd, as well as most of the launched astronauts and cosmonauts.
[edit]ReferencesCited References^ Silver, H Ward (2004-04-23). Amateur Radio for Dummies. Indianapolis: Wiley Publishing. ISBN 0764559877. OCLC 55092631. ^ [1969] (2003) International Code of Signals. Bethesda, MD: National Imagery and Mapping Agency. Pub. 102. Retrieved on 2007-01-10. ^ Galbraith, E Art. "KH6BB and "Mighty Mo," the Battleship Missouri", ARRL.org, 2003-08-23. Retrieved on 2007-01-10. ^ Taggart, Ralph E (April 1993). "An Introduction to Amateur Television". QST via ARRL.org: 19—23. Retrieved on 2007-06-02. ^ Taylor, Joe. "WSJT: New Software for VHF Meteor-Scatter Communication", QST via ARRL.org, pp. 36—41. Retrieved on 2007-01-11. ^ ARISS: Amateur Radio on the International Space Station. ARRL.org. Retrieved on 2007-01-10.^ Jurrens, Gerald. Astronaut (and Former Astronaut) Hams. gjurrens at Tellurian.com. Retrieved on 2007-01-10.^ Haag, Jerry. Principles of Amateur Radio Net Control. SCC-AREA-RACES.org. Retrieved on 2007-01-10.^ FCC to Drop Morse Testing for All Amateur License Classes. ARRL.org (2006-12-19). Retrieved on 2007-05-16.^ FCC Report and Order 06-178A1 7. Federal Communications Commission (2006-12-19). Retrieved on 2007-05-16.^ Amateur Radio (Intermediate) Licence (A) or (B) Terms, Provisions and Limitations Booklet BR68/I. Ofcom.org.uk. Retrieved on 2007-06-02.^ Common Filing Task: Obtaining Vanity Call Sign. FCC.gov. Retrieved on 2007-06-02.General ReferencesStraw, R Dean (ed.) (October 2005). The ARRL Handbook for Radio Communications 2006, 83rd edition, Newington, CT: American Radio Relay League. ISBN 0-87259-949-3. OCLC 62026192. Bergquist, Carl J (2001-05-01). Ham Radio Operator's Guide, 2nd edition, Indianapolis: Prompt Publications. ISBN 0-7906-1238-0. OCLC 47051066. Dennison, Mike and Chris Lorek (eds.) (June 2005). Radio Communication Handbook, 8th edition, Potters Bar, Hertfordshire, England: Radio Society of Great Britain. ISBN 1-90508608-3. OCLC 123027893. Poole, Ian D (2001-10-31). HF Amateur Radio. Potters Bar, Hertfordshire, England: Radio Society of Great Britain. ISBN 1-872309-75-5. OCLC 47823876
