Amateur radio, often called ham radio, is a service that uses various types of radio communications equipment to communicate with other radio amateurs for public service, recreation and self-training. A participant is called a amateur radio operator, or a ham.

Amateur radio operators have personal radio communications with friends and even complete strangers, and often support their communities with emergency and disaster communications while increasing their personal knowledge of electronics and radio theory. An estimated six million people throughout the world are regularly involved with amateur radio.

The term "amateur" is not a reflection on the skills of the participants, which are often quite advanced; rather, amateur indicates that the associated radio broadcast spectrum cannot be used for commercial or money-making purposes.

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 such as Moonbounce, with its inherent signal-to-noise ratio advantages. Morse, using internationally agreed code groups, also facilitates communications between amateurs who speak different languages. 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 low frequency bands, but following changes in international regulations in 2003, many countries have now dropped this requirement (eg. Italy in 2005 and the United States  in 2007).

Modern personal computers have led to a boom in digital modes such as radioteletype, which previously required electromechanical equipment. Hams led the development of packet radio, which has even used protocols such as TCP/IP since the 1970s. This 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 and radio nodes, while IRLP has allowed easy linking together of repeaters. Other modes, such as FSK441 using software 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.

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  can also 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. Hams are also often able to make contact with the International Space Station (ISS), as 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 be topical, covering specific interests shared by a group.

Licensing

In all countries, amateur radio operators are required to pass a licensing exam displaying knowledge and understanding of key concepts. 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. 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 require type-approved equipment restricted in frequency range and power.

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.

Newcomers

Many people start their involvement 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 radio 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, and the American Radio Relay League, Radio Amateurs of Canada. In Italy the most important societies is the Associazione Radioamatori Italiani.

Callsigns

Upon 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. In certain jurisdictions, an operator may also select a "vanity" callsign.

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 ATV) transmissions and high-speed data networks.

A distinguishing privilege of an amateur radio license is the ability to make relatively free use of variable frequency oscillators to control transmitter frequencies. The only other service allowed this privilege is the military. All other radio services must use 'type approved' transmitters that transmit on crystal-controlled fixed frequencies.

Although allowable power levels are moderate by commercial standards, they are sufficient to enable global communication. Power limits vary from country to country and between license classes within a country. For example, the power limits for the highest available license classes in a few selected countries 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.

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. Other host countries require that the visiting ham apply for a formal permit, or even a new host country-issued license, in advance.

Based upon  WIkipedia - the free encyclopedia