Amateur radio (also called “ham” radio) is the use of designated radio frequency spectra for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication. The term “amateur” is used to specify “a duly authorised person interested in radioelectric practice with a purely personal aim and without pecuniary interest;” (either direct monetary or other similar reward) and to differentiate it from commercial broadcasting, public safety (such as police and fire), or professional two-way radio services (such as maritime, aviation, taxis, etc.).
The amateur radio service (amateur service and amateur satellite service) is established by the International Telecommunication Union (ITU) through the International Telecommunication Regulations. National governments regulate technical and operational characteristics of transmissions and issue individual stations licenses with an identifying call sign. Prospective amateur operators are tested for their understanding of key concepts in electronics and the host government’s radio regulations. Radio amateurs use a variety of voice, text, image, and data communications modes and have access to frequency allocations throughout the RF spectrum to enable communication across a city, region, country, continent, the world, or even into space.Amateur radio is officially represented and coordinated by the International Amateur Radio Union (IARU), which is organized in three regions and has as its members the national amateur radio societies which exist in most countries. According to an estimate made in 2011 by the American Radio Relay League, two million people throughout the world are regularly involved with amateur radio. About 830,000 amateur radio stations are located in IARU Region 2 (the Americas) followed by IARU Region 3 (South and East Asia and the Pacific Ocean) with about 750,000 stations. A significantly smaller number, about 400,000, are located in IARU Region 1 (Europe, Middle East, CIS, Africa).
The origins of amateur radio can be traced to the late 19th century, but amateur radio as practiced today began in the early 20th century. The First Annual Official Wireless Blue Book of the Wireless Association of America, produced in 1909, contains the first listing of amateur radio stations. This first radio callbook lists wireless telegraph stations in Canada and the United States, including 89 amateur radio stations. As with radio in general, the birth of amateur radio was strongly associated with various amateur experimenters and hobbyists. Throughout its history, amateur radio enthusiasts have significantly contributed 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. Ham radio can also be used in the classroom to teach English, map skills, geography, math, science and computer skills.
The term “ham radio” was first a pejorative that mocked amateur radio operators with a 19th-century term for being bad at something, like “ham-fisted” or “ham actor”. It had already been used for bad wired telegraph operators.
Subsequently, the community adopted it as a welcome moniker, much like the “Know-Nothing Party”, or other groups and movements throughout history. Other, more entertaining explanations have grown up throughout the years, but they are apocryphal.
Activities and practices
The many facets of amateur radio attract practitioners with a wide range of interests. Many amateurs begin with a fascination of radio communication and then combine other personal interests to make pursuit of the hobby rewarding. Some of the focal areas amateurs pursue include radio contesting, radio propagation study, public service communication, technical experimentation, and computer networking.
Amateur radio operators use various modes of transmission to communicate. The two most common modes for voice transmissions are frequency modulation (FM) and single sideband (SSB). FM offers high quality audio signals, while SSB is better at long distance communication when bandwidth is restricted.
Radiotelegraphy using Morse code, also known as “CW” from “continuous wave”, is the wireless extension of land line (wired) telegraphy developed by Samuel Morse and dates to the earliest days of radio. Although computer-based (digital) modes and methods have largely replaced CW for commercial and military applications, many amateur radio operators still enjoy using the CW mode—particularly on the shortwave bands and for experimental work, such as earth-moon-earth communication, because of its inherent signal-to-noise ratio advantages. Morse, using internationally agreed message encodings such as the Q code, enables communication between amateurs who speak different languages. It is also popular with homebrewers and in particular with “QRP” or very-low-power enthusiasts, as CW-only transmitters are simpler to construct, and the human ear-brain signal processing system can pull weak CW signals out of the noise where voice signals would be totally inaudible. A similar “legacy” mode popular with home constructors is amplitude modulation (AM), pursued by many vintage amateur radio enthusiasts and aficionados of vacuum tube technology.
Demonstrating a proficiency in Morse code was for many years a requirement to obtain an amateur license to transmit on frequencies below 30 MHz. Following changes in international regulations in 2003, countries are no longer required to demand proficiency.The United States Federal Communications Commission, for example, phased out this requirement for all license classes on February 23, 2007.
Modern personal computers have encouraged the use of digital modes such as radioteletype (RTTY) which previously required cumbersome mechanical equipment. Hams led the development of packet radio in the 1970s, which has employed protocols such asAX.25 and TCP/IP. Specialized digital modes such as PSK31 allow 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 and radio nodes, while IRLP has allowed the linking of repeaters to provide greater coverage area. Automatic link establishment (ALE) has enabled continuous amateur radio networks to operate on the high frequency bands with global coverage. Other modes, such as FSK441 using software such as WSJT, are used for weak signal modes including meteor scatter and moonbounce communications.
Fast scan amateur television has gained popularity as hobbyists adapt inexpensive consumer video electronics like camcorders and video cards in PCs. Because of the wide bandwidth and stable signals required, amateur television is typically found in the 70 cm(420 MHz–450 MHz) frequency range, though there is also limited use on 33 cm (902 MHz–928 MHz), 23 cm (1240 MHz–1300 MHz) and higher. These requirements also effectively limit the signal range to between 20 and 60 miles (30 km–100 km).
Linked repeater systems, however, can allow transmissions of VHF and higher frequencies across hundreds of miles. Repeaters are usually located on heights of land or tall structures and allow operators to communicate over hundreds of miles using hand-held or mobile transceivers. Repeaters can also be linked together by using other amateur radio bands, landline, or the Internet.
Amateur radio satellites can be accessed, some using a hand-held transceiver (HT), even, at times, using the factory “rubber duck” antenna. Hams also use the moon, the aurora borealis, and the ionized trails of meteors as reflectors of radio waves. Hams can also contact the International Space Station (ISS) because many astronauts and cosmonauts are licensed as amateur radio operators.
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”. Nets can allow operators to learn procedures for emergencies, be an informal round table, or cover specific interests shared by a group.
Amateur radio operators, using battery- or generator-powered equipment, often provide essential communications services when regular channels are unavailable due to natural disaster or other disruptive events.
All countries that license citizens to use amateur radio require operators to display knowledge and understanding of key concepts, usually by passing an exam; however some authorities also recognize certain educational or professional qualifications (such as a degree in electrical engineering) in lieu. In response, hams receive operating privileges in larger segments of the radio frequency spectrum using a wide variety of communication techniques with higher power levels permitted compared to unlicensed personal radio services such as CB radio, Family Radio Service or PMR446 that require type-approved equipment restricted in frequency, range, and power.
Amateur licensing is a routine civil administrative matter in many countries. Amateurs therein must 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. A series of exams are often available, each progressively more challenging and granting more privileges: greater frequency availability, higher power output, permitted experimentation, and in some countries, distinctive call signs. Some countries, such as the United Kingdom and Australia, have begun requiring a practical training course in addition to the written exams in order to obtain a beginner’s license, which they call a Foundation License.
Amateur radio licensing in the United States exemplifies the way in which some countries award different levels of amateur radio licenses based on technical knowledge: three sequential levels of licensing exams (Technician Class, General Class and Amateur Extra Class) are currently offered, which allow operators who pass them access to larger portions of the Amateur Radio spectrum and more desirable (shorter) call signs.
In some countries, an amateur radio license is necessary in order to purchase or possess amateur radio equipment. An amateur radio license is only valid in the country in which it is issued or in another country that has a reciprocal licensing agreement with the issuing country.
Both the requirements for and privileges granted to a licensee vary from country to country, but generally follow the international regulations and standards established by the International Telecommunication Union andWorld Radio Conferences.
In most countries, an individual will be assigned a call sign with their license. In some countries, a separate “station license” is required for any station used by an amateur radio operator. Amateur radio licenses may also be granted to organizations or clubs. Some countries only allow ham radio operators to operate club stations. Others, such as Syria and Cuba restrict all operation by foreigners to club stations only. Radio transmission permits are closely controlled by nations’ governments because clandestine uses of radio can be made, and, because radio waves propagate beyond national boundaries, radio is an international matter.
Prospective amateur radio operators are examined on understanding of the key concepts of electronics, radio equipment, antennas, radio propagation, RF safety, and the radio regulations of the government granting the license. These examinations are sets of questions typically posed in either a short answer or multiple-choice format. Examinations can be administered by bureaucrats, non-paid certified examiners, or previously licensed amateur radio operators.
The ease with which an individual can acquire an amateur radio license varies from country to country. In some countries, examinations may be offered only once or twice a year in the national capital and can be inordinately bureaucratic (for example in India) or challenging because some amateurs must undergo difficult security approval (as in Iran). Currently only Yemen and North Korea do not issue amateur radio licenses to their citizens, although in both cases a limited number of foreign visitors have been permitted to obtain amateur licenses in the past decade. Some developing countries, especially those in Africa, Asia, and Latin America, require the payment of annual license fees that can be prohibitively expensive for most of their citizens. A few small countries may not have a national licensing process and may instead require prospective amateur radio operators to take the licensing examinations of a foreign country. In countries with the largest numbers of amateur radio licensees, such as Japan, the United States, Canada, and most of the countries in Europe, there are frequent license examinations opportunities in major cities.
Granting a separate license to a club or organization generally requires that an individual with a current and valid amateur radio license who is in good standing with the telecommunications authority assumes responsibility for any operations conducted under the club license or club call sign. A few countries may issue special licenses to novices or beginners that do not assign the individual a call sign but instead require the newly licensed individual to operate from stations licensed to a club or organization for a period of time before a higher class of license can be acquired.
Source : http://en.wikipedia.org/wiki/Amateur_radio