RADIO
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light.^[1] Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space. Information is carried by systematically changing (modulating) some property of the radiated waves, such as amplitude, frequency, phase, or pulse width. When radio waves pass an electrical conductor, the oscillating fields induce an alternating current in the conductor. This can be detected and transformed into sound or other signals that carry information.

Contents [hide] 1 Etymology 2 Processes 2.1 Electromagnetic spectrum 3 History 3.1 19th century 3.2 20th century 4 Uses of radio 4.1 Audio 4.2 Telephony 4.3 Video 4.4 Navigation 4.5 Radar 4.6 Data (digital radio) 4.7 Heating 4.8 Amateur radio service 4.9 Unlicensed radio services 4.10 Radio control (RC) 5 See also 6 References 7 Further reading 8 External links

[edit] Etymology

The etymology of "radio" or "radiotelegraphy" reveals that it was called "wireless telegraphy", which was shortened to "wireless" in Britain. The prefix radio- in the sense of wireless transmission, was first recorded in the word radioconductor, a description provided by the French physicist Édouard Branly in 1897. It is based on the verb to radiate (in Latin "radius" means "spoke of a wheel, beam of light, ray"). This word also appears in a 1907 article by Lee De Forest, it was adopted by the United States Navy in 1912, and became common by the time of the first commercial broadcasts in the United States in the 1920s. (The noun "broadcasting" itself came from an agricultural term, meaning "scattering seeds widely".) The term was then adopted by other languages in Europe and Asia. British Commonwealth countries continued to mainly use the term "wireless" until the mid-20th century, though the magazine of the BBC in the UK has been called Radio Times ever since it was first published in the early 1920s.
In recent years the term "wireless" has gained renewed popularity through the rapid growth of short-range computer networking, e.g., Wireless Local Area Network (WLAN), Wi-Fi, and Bluetooth, as well as mobile telephony, e.g., GSM and UMTS. Today, the term "radio" often refers to the actual transceiver device or chip, whereas "wireless" refers to the system and/or method used for radio communication; hence one talks about radio transceivers and Radio Frequency Identification (RFID), but about wireless devices and wireless sensor networks.

[edit] Processes

Radio systems used for communications will have the following elements. With more than 100 years of development, each process is implemented by a wide range of methods, specialized for different communications purposes.
Each system contains a transmitter. This consists of a source of electrical energy, producing alternating current of a desired frequency of oscillation. The transmitter contains a system to modulate (change) some property of the energy produced to impress a signal on it. This modulation might be as simple as turning the energy on and off, or altering more subtle properties such as amplitude, frequency, phase, or combinations of these properties. The transmitter sends the modulated electrical energy to a tuned resonant antenna; this structure converts the rapidly changing alternating current into an electromagnetic wave that can move through free space (sometimes with a particular polarization).
Electromagnetic waves travel through space either directly, or have their path altered by reflection, refraction or diffraction. The intensity of the waves diminishes due to geometric dispersion (the inverse-square law); some energy may also be absorbed by the intervening medium in some cases. Noise will generally alter the desired signal; this electromagnetic interference comes from natural sources, as well as from artificial sources such as other transmitters and accidental radiators. Noise is also produced at every step due to the inherent properties of the devices used. If the magnitude of the noise is large enough, the desired signal will no longer be discernible; this is the fundamental limit to the range of radio communications.
The electromagnetic wave is intercepted by a tuned receiving antenna; this structure captures some of the energy of the wave and returns it to the form of oscillating electrical currents. At the receiver, these currents are demodulated, which is conversion to a usable signal form by a detector sub-system. The receiver is "tuned" to respond preferentially to the desired signals, and reject undesired signals.
Early radio systems relied entirely on the energy collected by an antenna to produce signals for the operator. Radio became more useful after the invention of electronic devices such as the vacuum tube and later the transistor, which made it possible to amplify weak signals. Today radio systems are used for applications from walkie-talkie children's toys to the control of space vehicles, as well as for broadcasting, and many other applications.

[edit] Electromagnetic spectrum

Main article: Electromagnetic spectrum

Radio frequencies occupy the range from a few tens of hertz to three hundred gigahertz, although commercially important uses of radio use only a small part of this spectrum.^[2] Other types of electromagnetic radiation, with frequencies above the RF range, are microwave, infrared, visible light, ultraviolet, X-rays and gamma rays. Since the energy of an individual photon of radio frequency is too low to remove an electron from an atom, radio waves are classified as non-ionizing radiation.

[edit] History

Main article: History of radio

[edit] 19th century

Main article: Invention of radio

The meaning and usage of the word "radio" has developed in parallel with developments within the field of communications and can be seen to have three distinct phases: electromagnetic waves and experimentation; wireless communication and technical development; and radio broadcasting and commercialization. Many individuals—inventors, engineers, developers, businessmen - contributed to produce the modern idea of radio and thus the origins and 'invention' are multiple and controversial. Early radio designs could not transmit sound or speech and were called the "wireless telegraph".
Development from a laboratory demonstration to a commercial entity spanned several decades and required the efforts of many practitioners. In 1878, David E. Hughes noticed that sparks could be heard in a telephone receiver when experimenting with his carbon microphone. He developed this carbon-based detector further and eventually could detect signals over a few hundred yards. He demonstrated his discovery to the Royal Society in 1880, but was told it was merely induction, and therefore abandoned further research.
Experiments, later patented, were undertaken by Thomas Edison and his employees of Menlo Park.^[3] Edison applied in 1885 to the U.S. Patent Office for his patent on an electrostatic coupling system between elevated terminals. The patent was granted as U.S. Patent 465,971 on December 29, 1891. The Marconi Company would later purchase rights to the Edison patent to protect them legally from lawsuits.^[4]

Tesla demonstrating wireless transmissions during his high frequency and potential lecture of 1891. After continued research, Tesla presented the fundamentals of radio in 1893.

In 1893, in St. Louis, Missouri, Nikola Tesla made devices for his experiments with electricity. Addressing the Franklin Institute in Philadelphia and the National Electric Light Association, he described and demonstrated the principles of his wireless work.^[5] The descriptions contained all the elements that were later incorporated into radio systems before the development of the vacuum tube. He initially experimented with magnetic receivers, unlike the coherers (detecting devices consisting of tubes filled with iron filings which had been invented by Temistocle Calzecchi-Onesti at Fermo in Italy in 1884) used by Guglielmo Marconi and other early experimenters.^[6]
A demonstration of wireless telegraphy took place in the lecture theater of the Oxford University Museum of Natural History on August 14, 1894, carried out by Professor Oliver Lodge and Alexander Muirhead. During the demonstration a radio signal was sent from the neighboring Clarendon laboratory building, and received by apparatus in the lecture theater.
In 1895 Alexander Stepanovich Popov built his first radio receiver, which contained a coherer. Further refined as a lightning detector, it was presented to the Russian Physical and Chemical Society on May 7, 1895. A depiction of Popov's lightning detector was printed in the Journal of the Russian Physical and Chemical Society the same year. Popov's receiver was created on the improved basis of Lodge's receiver, and originally intended for reproduction of its experiments.
In 1895, Marconi built a wireless system capable of transmitting signals at long distances (1.5 mi./ 2.4 km).^[7][8] In radio transmission technology, early public experimenters had made short distance broadcasts.^[9] Marconi achieved long range signalling due to a wireless transmitting apparatus and a radio receiver claimed by him.^[10][11] From Marconi's experiments, the phenomenon that transmission range is proportional to the square of antenna height is known as "Marconi's law".^[12] This formula represents a physical law that radio devices use. Marconi's experimental apparatus proved to be a complete, commercially successful radio transmission system.^[11][13][14] According to the Proceedings of the United States Naval Institute in 1899, the Marconi instruments had a "[...] coherer, principle of which was discovered some twenty years ago, [and was] the only electrical instrument or device contained in the apparatus that is at all new".^[15]

Telephone Herald in Budapest, Hungary (1901).

In 1896, Marconi was awarded British patent 12039, Improvements in transmitting electrical impulses and signals and in apparatus there-for, for radio. In 1897, he established a radio station on the Isle of Wight, England. Marconi opened his "wireless" factory in Hall Street, Chelmsford, England in 1898, employing around 50 people. Shortly after the 1900s, Marconi held the patent rights for radio.

[edit] 20th century

The next advancement was the vacuum tube detector, invented by Westinghouse engineers. On Christmas Eve, 1906, Reginald Fessenden used a synchronous rotary-spark transmitter for the first radio program broadcast, from Ocean Bluff-Brant Rock, Massachusetts. Ships at sea heard a broadcast that included Fessenden playing O Holy Night on the violin and reading a passage from the Bible. This was, for all intents and purposes, the first transmission of what is now known as amplitude modulation or AM radio. The first radio news program was broadcast August 31, 1920 by station 8MK in Detroit, Michigan, which survives today as all-news format station WWJ under ownership of the CBS network. The first college radio station began broadcasting on October 14, 1920, from Union College, Schenectady, New York under the personal call letters of Wendell King, an African-American student at the school.^[16] That month 2ADD, later renamed WRUC in 1947, aired what is believed to be the first public entertainment broadcast in the United States, a series of Thursday night concerts initially heard within a 100-mile (160 km) radius and later for a 1,000-mile (1,600 km) radius. In November 1920, it aired the first broadcast of a sporting event.^[16][17] At 9 pm on August 27, 1920, Sociedad Radio Argentina aired a live performance of Richard Wagner's Parsifal opera from the Coliseo Theater in downtown Buenos Aires. Only about twenty homes in the city had receivers to tune in this radio program. Meanwhile, regular entertainment broadcasts commenced in 1922 from the Marconi Research Centre at Writtle, England.
Sports broadcasting began at this time as well, including the first broadcast college football game.^[18]

Patent rights in the United States during the 1900s.

In 1943 the United States Supreme Court upheld Tesla's patent for radio, number 645,576 (1897), with the supreme court's justification that claim 16 in Marconi's related patent, number 763,772 (1904), contained nothing new not having been published earlier and registered by Tesla, Lodge, and others. After years of patent battles by Marconi's company, the United States Supreme Court, in the 1943 case "Marconi Wireless Telegraph co. of America v. United States", held regarding the priority of engineering advances concerning the invention of radio that "[but] it is now held that in the important advance upon his basic patent Marconi did nothing that had not already been seen and disclosed".^[19][20] The decision effectively awarded priority of the invention of radio to Tesla and his 1893 presentation in St. Louis.^[21] Although Marconi claimed that he had no knowledge of prior art taken from Tesla's patents, the supreme court considered his claim false.^[22] In addition to the June 21, 1943 ruling made by the supreme court, the United States Court of Claims also invalidated the fundamental Marconi patent earlier, in 1935.^[23] This case defined radio by the statement: "A radio communication system requires two tuned circuits each at the transmitter and receiver, all four tuned to the same frequency."^[24] Because Tesla's 1897 patent for radio was intended for general transmission of energy, the court determined that Tesla's patent clearly was the first to disclose a system which could be used for wireless communication of intelligible messages (such as human voice and music) and used the four-circuit tuned combination.^[25] In contrast, related developments in the United Kingdom saw the British High Court uphold Marconi's British Patent 7,777 that was issued on April 26, 1900. This British patent held by Marconi disclosed a four-circuit system, which was strikingly similar to a four-circuit system disclosed in U.S. patent #645,576 that was issued earlier to Tesla on March 20, 1900. On the matter of invention, it is held that Marconi knowingly and unknowingly used the scientific and experimental work of many others who were devising their own radio tuning apparatus' around the same time, such as the work of American electrical engineer John Stone Stone who was issued several U.S. patents between 1904 and 1908. However, what made Marconi more successful than any other was his ability to commercialize radio and its associated equipment into a global business.^[26]

An American girl listens to a radio during the Great Depression.

One of the first developments in the early 20th century was that aircraft used commercial AM radio stations for navigation. This continued until the early 1960s when VOR systems became widespread.^[27] In the early 1930s, single sideband and frequency modulation were invented by amateur radio operators. By the end of the decade, they were established commercial modes. Radio was used to transmit pictures visible as television as early as the 1920s. Commercial television transmissions started in North America and Europe in the 1940s.
In 1954, the Regency company introduced a pocket transistor radio, the TR-1, powered by a "standard 22.5 V Battery". In 1955, the newly formed Sony company introduced its first transistorized radio.^[28] It was small enough to fit in a vest pocket, and able to be powered by a small battery. It was durable, because it had no vacuum tubes to burn out. Over the next 20 years, transistors replaced tubes almost completely except for very high-power transmitter uses. By 1963, color television was being regularly broadcast commercially (though not all broadcasts or programs were in color), and the first (radio) communication satellite, Telstar, was launched. In the late 1960s, the U.S. long-distance telephone network began to convert to a digital network, employing digital radios for many of its links. In the 1970s, LORAN became the premier radio navigation system. Soon, the U.S. Navy experimented with satellite navigation, culminating in the invention and launch of the GPS constellation in 1987. In the early 1990s, amateur radio experimenters began to use personal computers with audio cards to process radio signals. In 1994, the U.S. Army and DARPA launched an aggressive, successful project to construct a software-defined radio that can be programmed to be virtually any radio by changing its software program. Digital transmissions began to be applied to broadcasting in the late 1990s.

[edit] Uses of radio

Early uses were maritime, for sending telegraphic messages using Morse code between ships and land. The earliest users included the Japanese Navy scouting the Russian fleet during the Battle of Tsushima in 1905. One of the most memorable uses of marine telegraphy was during the sinking of the RMS Titanic in 1912, including communications between operators on the sinking ship and nearby vessels, and communications to shore stations listing the survivors.
Radio was used to pass on orders and communications between armies and navies on both sides in World War I; Germany used radio communications for diplomatic messages once it discovered that its submarine cables had been tapped by the British. The United States passed on President Woodrow Wilson's Fourteen Points to Germany via radio during the war. Broadcasting began from San Jose, California in 1909,^[29] and became feasible in the 1920s, with the widespread introduction of radio receivers, particularly in Europe and the United States. Besides broadcasting, point-to-point broadcasting, including telephone messages and relays of radio programs, became widespread in the 1920s and 1930s. Another use of radio in the pre-war years was the development of detection and locating of aircraft and ships by the use of radar (RAdio Detection And Ranging).
Today, radio takes many forms, including wireless networks and mobile communications of all types, as well as radio broadcasting. Before the advent of television, commercial radio broadcasts included not only news and music, but dramas, comedies, variety shows, and many other forms of entertainment (the era from 1930 to the mid-1950s is commonly called radio's "Golden Age"). Radio was unique among methods of dramatic presentation in that it used only sound. For more, see radio programming.

[edit] Audio

A Fisher 500 AM/FM hi-fi receiver from 1959.

AM radio uses amplitude modulation, in which the amplitude of the transmitted signal is made proportional to the sound amplitude captured (transduced) by the microphone, while the transmitted frequency remains unchanged. Transmissions are affected by static and interference because lightning and other sources of radio emissions on the same frequency add their amplitudes to the original transmitted amplitude. In the early part of the 20th century, American AM radio stations broadcast with powers as high as 500 kW, and some could be heard worldwide; these stations' transmitters were commandeered for military use by the US Government during World War II. Currently, the maximum broadcast power for a civilian AM radio station in the United States and Canada is 50 kW, and the majority of stations that emit signals this powerful were grandfathered in (see List of 50kw AM radio stations in the USA). In 1986 KTNN received the last granted 50,000 watt license. These 50 kW stations are generally called "clear channel" stations (not to be confused with Clear Channel Communications), because within North America each of these stations has exclusive use of its broadcast frequency throughout part or all of the broadcast day.

Bush House, home of the BBC World Service.

FM broadcast radio sends music and voice with higher fidelity than AM radio. In frequency modulation, amplitude variation at the microphone causes the transmitter frequency to fluctuate. Because the audio signal modulates the frequency and not the amplitude, an FM signal is not subject to static and interference in the same way as AM signals. Due to its need for a wider bandwidth, FM is transmitted in the Very High Frequency (VHF, 30 MHz to 300 MHz) radio spectrum. VHF radio waves act more like light, traveling in straight lines; hence the reception range is generally limited to about 50–100 miles. During unusual upper atmospheric conditions, FM signals are occasionally reflected back towards the Earth by the ionosphere, resulting in long distance FM reception. FM receivers are subject to the capture effect, which causes the radio to only receive the strongest signal when multiple signals appear on the same frequency. FM receivers are relatively immune to lightning and spark interference.
High power is useful in penetrating buildings, diffracting around hills, and refracting in the dense atmosphere near the horizon for some distance beyond the horizon. Consequently, 100,000 watt FM stations can regularly be heard up to 100 miles (160 km) away, and farther (e.g., 150 miles, 240 km) if there are no competing signals. A few old, "grandfathered" stations do not conform to these power rules. WBCT-FM (93.7) in Grand Rapids, Michigan, USA, runs 320,000 watts ERP, and can increase to 500,000 watts ERP by the terms of its original license. Such a huge power level does not usually help to increase range as much as one might expect, because VHF frequencies travel in nearly straight lines over the horizon and off into space. Nevertheless, when there were fewer FM stations competing, this station could be heard near Bloomington, Illinois, USA, almost 300 miles (500 km) away.^{[citation needed]}
FM subcarrier services are secondary signals transmitted in a "piggyback" fashion along with the main program. Special receivers are required to utilize these services. Analog channels may contain alternative programming, such as reading services for the blind, background music or stereo sound signals. In some extremely crowded metropolitan areas, the sub-channel program might be an alternate foreign language radio program for various ethnic groups. Sub-carriers can also transmit digital data, such as station identification, the current song's name, web addresses, or stock quotes. In some countries, FM radios automatically re-tune themselves to the same channel in a different district by using sub-bands.
Aviation voice radios use VHF AM. AM is used so that multiple stations on the same channel can be received. (Use of FM would result in stronger stations blocking out reception of weaker stations due to FM's capture effect). Aircraft fly high enough that their transmitters can be received hundreds of miles (or kilometres) away, even though they are using VHF.

Degen DE1103, an advanced world mini-receiver with single sideband modulation and dual conversion

Marine voice radios can use single sideband voice (SSB) in the shortwave High Frequency (HF—3 MHz to 30 MHz) radio spectrum for very long ranges or narrowband FM in the VHF spectrum for much shorter ranges. Narrowband FM sacrifices fidelity to make more channels available within the radio spectrum, by using a smaller range of radio frequencies, usually with five kHz of deviation, versus the 75 kHz used by commercial FM broadcasts, and 25 kHz used for TV sound.
Government, police, fire and commercial voice services also use narrowband FM on special frequencies. Early police radios used AM receivers to receive one-way dispatches.
Civil and military HF (high frequency) voice services use shortwave radio to contact ships at sea, aircraft and isolated settlements. Most use single sideband voice (SSB), which uses less bandwidth than AM. On an AM radio SSB sounds like ducks quacking, or the adults in a Charlie Brown cartoon. Viewed as a graph of frequency versus power, an AM signal shows power where the frequencies of the voice add and subtract with the main radio frequency. SSB cuts the bandwidth in half by suppressing the carrier and one of the sidebands. This also makes the transmitter about three times more powerful, because it doesn't need to transmit the unused carrier and sideband.
TETRA, Terrestrial Trunked Radio is a digital cell phone system for military, police and ambulances. Commercial services such as XM, WorldSpace and Sirius offer encrypted digital Satellite radio.

[edit] Telephony

Mobile phones transmit to a local cell site (transmitter/receiver) that ultimately connects to the public switched telephone network (PSTN) through an optic fiber or microwave radio and other network elements. When the mobile phone nears the edge of the cell site's radio coverage area, the central computer switches the phone to a new cell. Cell phones originally used FM, but now most use various digital modulation schemes. Recent developments in Sweden (such as DROPme) allow for the instant downloading of digital material from a radio broadcast (such as a song) to a mobile phone.
Satellite phones use satellites rather than cell towers to communicate.

[edit] Video

Television sends the picture as AM and the sound as AM or FM, with the sound carrier a fixed frequency (4.5 MHz in the NTSC system) away from the video carrier. Analog television also uses a vestigial sideband on the video carrier to reduce the bandwidth required.
Digital television uses 8VSB modulation in North America (under the ATSC digital television standard), and COFDM modulation elsewhere in the world (using the DVB-T standard). A Reed–Solomon error correction code adds redundant correction codes and allows reliable reception during moderate data loss. Although many current and future codecs can be sent in the MPEG transport stream container format, as of 2006 most systems use a standard-definition format almost identical to DVD: MPEG-2 video in Anamorphic widescreen and MPEG layer 2 (MP2) audio. High-definition television is possible simply by using a higher-resolution picture, but H.264/AVC is being considered as a replacement video codec in some regions for its improved compression. With the compression and improved modulation involved, a single "channel" can contain a high-definition program and several standard-definition programs.

[edit] Navigation

All satellite navigation systems use satellites with precision clocks. The satellite transmits its position, and the time of the transmission. The receiver listens to four satellites, and can figure its position as being on a line that is tangent to a spherical shell around each satellite, determined by the time-of-flight of the radio signals from the satellite. A computer in the receiver does the math.
Radio direction-finding is the oldest form of radio navigation. Before 1960 navigators used movable loop antennas to locate commercial AM stations near cities. In some cases they used marine radiolocation beacons, which share a range of frequencies just above AM radio with amateur radio operators. LORAN systems also used time-of-flight radio signals, but from radio stations on the ground. VOR (Very High Frequency Omnidirectional Range), systems (used by aircraft), have an antenna array that transmits two signals simultaneously. A directional signal rotates like a lighthouse at a fixed rate. When the directional signal is facing north, an omnidirectional signal pulses. By measuring the difference in phase of these two signals, an aircraft can determine its bearing or radial from the station, thus establishing a line of position. An aircraft can get readings from two VORs and locate its position at the intersection of the two radials, known as a "fix." When the VOR station is collocated with DME (Distance Measuring Equipment), the aircraft can determine its bearing and range from the station, thus providing a fix from only one ground station. Such stations are called VOR/DMEs. The military operates a similar system of navaids, called TACANs, which are often built into VOR stations. Such stations are called VORTACs. Because TACANs include distance measuring equipment, VOR/DME and VORTAC stations are identical in navigation potential to civil aircraft.

[edit] Radar

Radar (Radio Detection And Ranging) detects objects at a distance by bouncing radio waves off them. The delay caused by the echo measures the distance. The direction of the beam determines the direction of the reflection. The polarization and frequency of the return can sense the type of surface. Navigational radars scan a wide area two to four times per minute. They use very short waves that reflect from earth and stone. They are common on commercial ships and long-distance commercial aircraft.
General purpose radars generally use navigational radar frequencies, but modulate and polarize the pulse so the receiver can determine the type of surface of the reflector. The best general-purpose radars distinguish the rain of heavy storms, as well as land and vehicles. Some can superimpose sonar data and map data from GPS position.
Search radars scan a wide area with pulses of short radio waves. They usually scan the area two to four times a minute. Sometimes search radars use the Doppler effect to separate moving vehicles from clutter. Targeting radars use the same principle as search radar but scan a much smaller area far more often, usually several times a second or more. Weather radars resemble search radars, but use radio waves with circular polarization and a wavelength to reflect from water droplets. Some weather radar use the Doppler effect to measure wind speeds.

[edit] Data (digital radio)

2008 Pure One Classic digital radio

Most new radio systems are digital, see also: Digital TV, Satellite Radio, Digital Audio Broadcasting. The oldest form of digital broadcast was spark gap telegraphy, used by pioneers such as Marconi. By pressing the key, the operator could send messages in Morse code by energizing a rotating commutating spark gap. The rotating commutator produced a tone in the receiver, where a simple spark gap would produce a hiss, indistinguishable from static. Spark-gap transmitters are now illegal, because their transmissions span several hundred megahertz. This is very wasteful of both radio frequencies and power.
The next advance was continuous wave telegraphy, or CW (Continuous Wave), in which a pure radio frequency, produced by a vacuum tube electronic oscillator was switched on and off by a key. A receiver with a local oscillator would "heterodyne" with the pure radio frequency, creating a whistle-like audio tone. CW uses less than 100 Hz of bandwidth. CW is still used, these days primarily by amateur radio operators (hams). Strictly, on-off keying of a carrier should be known as "Interrupted Continuous Wave" or ICW or on-off keying (OOK).
Radioteletype equipment usually operates on short-wave (HF) and is much loved by the military because they create written information without a skilled operator. They send a bit as one of two tones using frequency-shift keying. Groups of five or seven bits become a character printed by a teleprinter. From about 1925 to 1975, radioteletype was how most commercial messages were sent to less developed countries. These are still used by the military and weather services.
Aircraft use a 1200 Baud radioteletype service over VHF to send their ID, altitude and position, and get gate and connecting-flight data. Microwave dishes on satellites, telephone exchanges and TV stations usually use quadrature amplitude modulation (QAM). QAM sends data by changing both the phase and the amplitude of the radio signal. Engineers like QAM because it packs the most bits into a radio signal when given an exclusive (non-shared) fixed narrowband frequency range. Usually the bits are sent in "frames" that repeat. A special bit pattern is used to locate the beginning of a frame.

Modern GPS receivers.

Communication systems that limit themselves to a fixed narrowband frequency range are vulnerable to jamming. A variety of jamming-resistant spread spectrum techniques were initially developed for military use, most famously for Global Positioning System satellite transmissions. Commercial use of spread spectrum began in the 1980s. Bluetooth, most cell phones, and the 802.11b version of Wi-Fi each use various forms of spread spectrum.
Systems that need reliability, or that share their frequency with other services, may use "coded orthogonal frequency-division multiplexing" or COFDM. COFDM breaks a digital signal into as many as several hundred slower subchannels. The digital signal is often sent as QAM on the subchannel.












                                                              ROBOT
A robot is a mechanical intelligent agent which can perform tasks on its own, or with guidance. In practice a robot is usually an electro-mechanical machine which is guided by computer and electronic programming. Robots can be autonomous or semi-autonomous and come in those two basic types: those which are used for research into human-like systems, such as ASIMO and TOPIO, as well as those into more defined and specific roles, such as Nano robots and Swarm robots; and helper robots which are used to make or move things or perform menial or dangerous tasks, such as Industrial robots or mobile or servicing robots. Another common characteristic is that, by its appearance or movements, a robot often conveys a sense that it has intent or agency of its own.
When societies first began developing, nearly all production and effort was the result of human labour, as well as with the aid of semi- and fully domesticated animals. As mechanical means of performing functions were discovered, and mechanics and complex mechanisms were developed, the need for human labour was reduced. Machinery was initially used for repetitive functions, such as lifting water and grinding grain. With technological advances more complex machines were slowly developed, such as those invented by Hero of Alexandria (in Egypt) in the 1st century AD, and the first half of the second millennium AD, such as the Automata of Al-Jazari in the 12th century AD (in medieval Iraq). They were not widely adopted as human labour, particularly slave labour, was still inexpensive compared to the capital-intensive machines. Men such as Leonardo Da Vinci in 1495 through to Jacques de Vaucanson in 1739, as well as rediscovering the Greek engineering methods, have made plans for and built automata and robots leading to books of designs such as the Japanese Karakuri zui (Illustrated Machinery) in 1796. As mechanical techniques developed through the Industrial age we find more practical applications such as Nikola Tesla in 1898, who designed a radio-controlled torpedo, and the Westinghouse Electric Corporation creation of Televox in 1926. From here we also find a more android development as designers tried to mimic more human-like features including designs such as those of biologist Makoto Nishimura in 1929 and his creation Gakutensoku, which cried and changed its facial expressions, and the more crude Elektro from Westinghouse in 1938.
Electronics then became the driving force of development instead of mechanics, with the advent of the first electronic autonomous robots created by William Grey Walter in Bristol, England, in 1948. The first digital and programmable robot was invented by George Devol in 1954 and was ultimately called the Unimate. Devol sold the first Unimate to General Motors in 1960 where it was used to lift pieces of hot metal from die casting machines in a plant in Trenton, New Jersey. Since then we have seen robots finally reach a more true assimilation of all technologies to produce robots such as ASIMO which can walk and move like a human. Robots have replaced slaves in the assistance of performing those repetitive and dangerous tasks which humans prefer not to do, or are unable to do due to size limitations, or even those such as in outer space or at the bottom of the sea where humans could not survive the extreme environments.
Man has developed an awareness of the problems associated with autonomous robots and how they may act in society. Fear of robot behaviour, such as Shelley's Frankenstein and the EATR, drive current practice in establishing what autonomy a robot should and should not be capable of. Thinking has developed through discussion of robot control and artificial intelligence (AI) and how its application should benefit society, such as those based around Asimov's three laws. Practicality still drives development forwards and robots are used in an increasingly wide variety of tasks such as vacuuming floors, mowing lawns, cleaning drains, investigating other planets, building cars, in entertainment and in warfare.

Contents [hide] 1 History 1.1 Ancient beginnings 1.2 Early modern developments 1.3 Modern developments 2 Etymology 3 Definitions 3.1 Defining characteristics 4 Modern robots 4.1 Mobile robot 4.2 Industrial robots (manipulating) 4.3 Service robot 5 Robots in society 5.1 Regional perspectives 5.2 Autonomy and ethical questions 5.3 Military robots 6 Contemporary uses 6.1 General-purpose autonomous robots 6.2 Factory robots 6.3 Dirty, dangerous, dull or inaccessible tasks 6.4 Military robots 6.5 Schools 6.6 Healthcare 6.7 Research robots 7 Future development 7.1 Technological trends 7.2 Technological development 7.3 Reading robot 8 Problems with implementing robots in society 8.1 Dangers and human harm 8.2 Robotic devices 8.3 Relationship to unemployment 9 Robots in popular culture 9.1 Literature 9.2 Problems depicted in popular culture 10 See also 11 References 12 Further reading 13 External links

[edit] History

Main article: History of robots

The idea of automata originates in the mythologies of many cultures around the world. Engineers and inventors from ancient civilizations, including Ancient China,^[3] Ancient Greece, and Ptolemaic Egypt,^[4] attempted to build self-operating machines, some resembling animals and humans. Early descriptions of automata include the artificial doves of Archytas,^[5] the artificial birds of Mozi and Lu Ban,^[6] a "speaking" automaton by Hero of Alexandria, a washstand automaton by Philo of Byzantium, and a human automaton described in the Lie Zi.^[3]

Timeline of robot and automata development [show]

Date	Significance	Robot name	Inventor
1st century AD and earlier	Descriptions of over a hundred machines and automata, including a fire engine, wind organ, coin-operated machine, and steam-powered aeliopile, in Pneumatica and Automata by Heron		Ctesibius, Philo, Heron, and others
1206	Early programmable automata	Robot band[7]	Al-Jazari
c. 1495	Designs for a humanoid robot	Mechanical knight	Leonardo da Vinci
1738	Mechanical duck that was able to eat, flap its wings, and excrete	Digesting Duck	Jacques de Vaucanson
19th century	Japanese mechanical toys that served tea, fired arrows, and painted	Karakuri toys	Hisashige Tanaka
1898	radio controlled robot boats, Tesla demonstrated the vessels to a crowd in an indoor pool at Madison Square Garden in New York City.	Telautomatons	Nikola Tesla
1921	First fictional automata called "robots" appear in the play R.U.R.	Rossum's Universal Robots	Karel Čapek
1928	Humanoid robot, based on a suit of armor with electrical actuators, exhibited at the annual exhibition of the Model Engineers Society in London	Eric	W. H. Richards
1930s	Humanoid robot exhibited at the 1939 and 1940 World's Fairs	Elektro	Westinghouse Electric Corporation
1948	Simple robots exhibiting biological behaviors[8]	Elsie and Elmer	William Grey Walter
1956	First commercial robot, from the Unimation company founded by George Devol and Joseph Engelberger, based on Devol's patents[9]	Unimate	George Devol
1961	First installed industrial robot	Unimate	George Devol
1963	First palletizing robot[10]	Palletizer	Fuji Yusoki Kogyo
1973	First robot with six electromechanically driven axes[11]	Famulus	KUKA Robotics
1975	Programmable universal manipulation arm, a Unimation product	PUMA	Victor Scheinman

[edit] Ancient beginnings

Many ancient mythologies include artificial people, such as the mechanical servants built by the Greek god Hephaestus^[12] (Vulcan to the Romans), the clay golems of Jewish legend and clay giants of Norse legend, and Galatea, the mythical statue of Pygmalion that came to life.
Since cerca 400 BCE, myths of Crete that were incorporated into Greek mythology include Talos, a man of bronze who guarded the Cretian island of Europa from pirates.
In ancient Greece, the Greek engineer Ctesibius (c. 270 BC) "applied a knowledge of pneumatics and hydraulics to produce the first organ and water clocks with moving figures."^[13][14] In the 4th century BC, the Greek mathematician Archytas of Tarentum postulated a mechanical steam-operated bird he called "The Pigeon". Hero of Alexandria (10–70 AD), a Greek mathematician and inventor, created numerous user-configurable automated devices, and described machines powered by air pressure, steam and water.^[15]
In ancient China, the 3rd century BC text of the Lie Zi describes an account of humanoid automata, involving a much earlier encounter between King Mu of Zhou (Chinese emperor 10th century BC) and a mechanical engineer known as Yan Shi, an 'artificer'. The latter proudly presented the king with a life-size, human-shaped figure of his mechanical 'handiwork' made of leather, wood, and artificial organs.^[3] There are also accounts of flying automata in the Han Fei Zi and other texts, which attributes the 5th century BC Mohist philosopher Mozi and his contemporary Lu Ban with the invention of artificial wooden birds (ma yuan) that could successfully fly.^[6] In 1066, the Chinese inventor Su Song built a water clock in the form of a tower which featured mechanical figurines which chimed the hours. The beginning of automata is associated with the invention of early Su Song's astronomical clock tower featured mechanical figurines that chimed the hours.^[16]
In the medieval Islamic world, Al-Jazari (1136–1206), a Muslim inventor during the Artuqid dynasty, designed and constructed a number of automated machines, including kitchen appliances, musical automata powered by water, and programmable automata.^[7][17] The robots appeared as four musicians on a boat in a lake, entertaining guests at royal drinking parties. His mechanism had a programmable drum machine with pegs (cams) that bumped into little levers that operated percussion instruments. The drummer could be made to play different rhythms and different drum patterns by moving the pegs to different locations.^[7][17]

• 

  Washstand automaton reconstruction, as described by Philo of Byzantium (Greece, 3rd century BC).
• 

  Al-Jazari's programmable automata
• 

  Tea-serving karakuri with mechanism. (Tokyo National Science Museum).
• 

  Su Song's astronomical clock tower showing the mechanical figurines which chimed the hours.

[edit] Early modern developments

In Renaissance Italy, Leonardo da Vinci (1452–1519) sketched plans for a humanoid robot around 1495. Da Vinci's notebooks, rediscovered in the 1950s, contain detailed drawings of a mechanical knight now known as Leonardo's robot, able to sit up, wave its arms and move its head and jaw.^[18] The design was probably based on anatomical research recorded in his Vitruvian Man. It is not known whether he attempted to build it.
In Japan, complex animal and human automata were built between the 17th to 19th centuries, with many described in the 18th century Karakuri zui (Illustrated Machinery, 1796). One such automaton was the karakuri ningyō, a mechanized puppet.^[19] Different variations of the karakuri existed: the Butai karakuri, which were used in theatre, the Zashiki karakuri, which were small and used in homes, and the Dashi karakuri which were used in religious festivals, where the puppets were used to perform reenactments of traditional myths and legends.
In France, between 1738 and 1739, Jacques de Vaucanson exhibited several life-sized automatons: a flute player, a pipe player and a duck. The mechanical duck could flap its wings, crane its neck, and swallow food from the exhibitor's hand, and it gave the illusion of digesting its food by excreting matter stored in a hidden compartment.^[20]

[edit] Modern developments

The Japanese craftsman Hisashige Tanaka (1799–1881), known as "Japan's Edison" or "Karakuri Giemon", created an array of extremely complex mechanical toys, some of which served tea, fired arrows drawn from a quiver, and even painted a Japanese kanji character.^[21] In 1898 Nikola Tesla publicly demonstrated a radio-controlled torpedo.^[22] Based on patents for "teleautomation", Tesla hoped to develop it into a weapon system for the US Navy.^[23][24]
In 1926, Westinghouse Electric Corporation created Televox, the first robot put to useful work. They followed Televox with a number of other simple robots, including one called Rastus, made in the crude image of a black man. In the 1930s, they created a humanoid robot known as Elektro for exhibition purposes, including the 1939 and 1940 World's Fairs.^[25][26] In 1928, Japan's first robot, Gakutensoku, was designed and constructed by biologist Makoto Nishimura.
The first electronic autonomous robots were created by William Grey Walter of the Burden Neurological Institute at Bristol, England in 1948 and 1949. They were named Elmer and Elsie. These robots could sense light and contact with external objects, and use these stimuli to navigate.^[27]
The first truly modern robot, digitally operated and programmable, was invented by George Devol in 1954 and was ultimately called the Unimate. Devol sold the first Unimate to General Motors in 1960, and it was installed in 1961 in a plant in Trenton, New Jersey to lift hot pieces of metal from a die casting machine and stack them.^[28] Devol’s patent for the first digitally operated programmable robotic arm represents the foundation of the modern robotics industry.^[29]
Commercial and industrial robots are now in widespread use performing jobs more cheaply or with greater accuracy and reliability than humans. They are also employed for jobs which are too dirty, dangerous or dull to be suitable for humans. Robots are widely used in manufacturing, assembly and packing, transport, earth and space exploration, surgery, weaponry, laboratory research, and mass production of consumer and industrial goods.^[30]

[edit] Etymology

See also: Glossary of robotics

A scene from Karel Čapek's 1920 play R.U.R. (Rossum's Universal Robots), showing three robots

The word robot was introduced to the public by the Czech interwar writer Karel Čapek in his play R.U.R. (Rossum's Universal Robots), published in 1920.^[31] The play begins in a factory that makes artificial people called robots, though they are closer to the modern ideas of androids, creatures who can be mistaken for humans. They can plainly think for themselves, though they seem happy to serve. At issue is whether the robots are being exploited and the consequences of their treatment.
Karel Čapek himself did not coin the word. He wrote a short letter in reference to an etymology in the Oxford English Dictionary in which he named his brother, the painter and writer Josef Čapek, as its actual originator.^[31]
In an article in the Czech journal Lidové noviny in 1933, he explained that he had originally wanted to call the creatures laboři ("workers", from Latin labor) or dělňasi (from Czech dělníci - "workers"). However, he did not like the word, and sought advice from his brother Josef, who suggested "roboti". The word robota means literally "corvée", "serf labor", and figuratively "drudgery" or "hard work" in Czech and also (more general) "work", "labor" in many Slavic languages (e.g.: Slovak, Polish, archaic Czech). Traditionally the robota was the work period a serf (corvée) had to give for his lord, typically 6 months of the year. The origin of the word is the Old Church Slavonic rabota "servitude" ("work" in contemporary Bulgarian and Russian), which in turn comes from the Indo-European root *orbh-.^[32] Serfdom was outlawed in 1848 in Bohemia, so at the time Čapek wrote R.U.R., usage of the term robota had broadened to include various types of work, but the obsolete sense of "serfdom" would still have been known.^[33] It is not clear from which language Čapek took the radix "robot(a)". This question is not irrelevant, because its answer could help to reveal an original Čapek´s conception of robots. If from the modern Czech language, the notion of robot should be understood as an „automatic serf“ (it means a subordinated creature without own will). If from Polish, Russian or Slovak (Karel Čapek and his brother were frequent visitors of Slovakia which in this time was a part of Czechoslovakia, because their father MUDr. Antonín Čapek from 1916 worked as a physician in Trenčianske Teplice.^[34]), the word robot would simply mean a „worker“ what is a more universal and neutral notion. The aspect of pronunciation probably also played a role in Čapek's final decision: In non-Slavic languages it is more easily to pronounce a word robot than dělňas or laboř.
The word robotics, used to describe this field of study, was coined by the science fiction writer Isaac Asimov. Asimov and John W. Campbell created the "Three Laws of Robotics" which are a recurring theme in his books. These have since been used by many others to define laws used in fact and fiction. Introduced in his 1942 short story "Runaround" the Laws state the following:

“

A robot may not injure a human being or, through inaction, allow a human being to come to harm. A robot must obey any orders given to it by human beings, except where such orders would conflict with the First Law. A robot must protect its own existence as long as such protection does not conflict with the First or Second Law.

”

[edit] Definitions

The word robot can refer to both physical robots and virtual software agents, but the latter are usually referred to as bots.^[35] There is no consensus on which machines qualify as robots but there is general agreement among experts, and the public, that robots tend to do some or all of the following: move around, operate a mechanical limb, sense and manipulate their environment, and exhibit intelligent behavior — especially behavior which mimics humans or other animals.
There is no one definition of robot which satisfies everyone and many people have their own.^[36] For example Joseph Engelberger, a pioneer in industrial robotics, once remarked: "I can't define a robot, but I know one when I see one."^[37] According to the Encyclopaedia Britannica a robot is "any automatically operated machine that replaces human effort, though it may not resemble human beings in appearance or perform functions in a humanlike manner".^[38] Merriam-Webster describes a robot as a "machine that looks like a human being and performs various complex acts (as walking or talking) of a human being", or a "device that automatically performs complicated often repetitive tasks", or a "mechanism guided by automatic controls".^[39]

• 

  The various types of robots
• 

  KITT (a fictitious robot) is mentally anthropomorphic
• 

  ASIMO is physically anthropomorphic

[edit] Defining characteristics

While there is no single correct definition of "robot,"^[40] a typical robot will have several, or possibly all, of the following characteristics.
It is an electric machine which has some ability to interact with physical objects and to be given electronic programming to do a specific task or to do a whole range of tasks or actions. It may also have some ability to perceive and absorb data on physical objects, or on its local physical environment, or to process data, or to respond to various stimuli. This is in contrast to a simple mechanical device such as a gear or a hydraulic press or any other item which has no processing ability and which does tasks through purely mechanical processes and motion.^{[citation needed]}

Mental agency

For robotic engineers, the physical appearance of a machine is less important than the way its actions are controlled. The more the control system seems to have agency of its own, the more likely the machine is to be called a robot. An important feature of agency is the ability to make choices. Higher-level cognitive functions, though, are not necessary, as shown by ant robots.^{[citation needed]}

• A clockwork car is never considered a robot.^{[citation needed]}
• A mechanical device able to perform some preset motions but with no ability to adapt (an automaton) is rarely considered a robot.^{[citation needed]}
• A remotely operated vehicle is sometimes considered a robot (or telerobot).^[41]
• A car with an onboard computer, like Bigtrak, which could drive in a programmable sequence, might be called a robot.^{[citation needed]}
• A self-controlled car which could sense its environment and make driving decisions based on this information, such as the 1990s driverless cars of Ernst Dickmanns or the entries in the DARPA Grand Challenge, would quite likely be called a robot.^{[citation needed]}
• A sentient car, like the fictional KITT, which can make decisions, navigate freely and converse fluently with a human, is usually considered a robot.^{[citation needed]}

Physical agency

However, for many laymen, if a machine appears able to control its arms or limbs, and especially if it appears anthropomorphic or zoomorphic (e.g. ASIMO or Aibo), it would be called a robot.^{[citation needed]}

• A player piano is rarely characterized as a robot.^[42]
• A CNC milling machine is very occasionally characterized as a robot.^{[citation needed]}
• A factory automation arm is almost always characterized as an industrial robot.^{[citation needed]}
• An autonomous wheeled or tracked device, such as a self-guided rover or self-guided vehicle, is almost always characterized as a mobile robot or service robot.^{[citation needed]}
• A zoomorphic mechanical toy, like Roboraptor, is usually characterized as a robot.^[43]
• A mechanical humanoid, like ASIMO, is almost always characterized as a robot, usually as a service robot.

                                                     ENCYCLOPEDIA INI DARI :http://en.wikipedia.org/wiki