Radio is the transmission of signals through free space by electromagnetic waves with frequencies significantly below visible light, in the radio frequency range, from about 3 kHz to 300 GHz. These waves are called ''radio waves''. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space.

Information, such as sound, is carried by systematically changing (modulating) some property of the radiated waves, such as their amplitude, frequency, phase, or pulse width. When radio waves strike an electrical conductor, the oscillating fields induce an alternating current in the conductor. The information in the waves can be extracted and transformed back into its original form.

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").

The word "radio" 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 adopted by other languages in Europe and Asia. British Commonwealth countries continued to commonly 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.

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.

Transmitter and modulation

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).

Amplitude modulation of a carrier wave works by varying the strength of the transmitted signal in proportion to the information being sent. For example, changes in the signal strength can be used to reflect the sounds to be reproduced by a speaker, or to specify the light intensity of television pixels. It was the method used for the first audio radio transmissions, and remains in use today. "AM" is often used to refer to the mediumwave broadcast band (see AM radio).

Frequency modulation varies the frequency of the carrier. The instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. Digital data can be sent by shifting the carrier's frequency among a set of discrete values, a technique known as frequency-shift keying.

FM is commonly used at VHF radio frequencies for high-fidelity broadcasts of music and speech (see FM broadcasting). Normal (analog) TV sound is also broadcast using FM.

Angle modulation alters the instantaneous phase of a carrier wave to transmit a signal. It is another term for Phase modulation.

Antennas and propagation

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.

Resonance

Electrical resonance of tuned circuits in radios allow individual stations to be selected. A resonant circuit will respond strongly to a particular frequency, and much less so to differing frequencies. This allows the radio receiver to discriminate between multiple signals differing in frequency.

Receiver and demodulation

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.

A ''radio receiver'' receives its input from an antenna, uses electronic filters to separate a wanted radio signal from all other signals picked up by this antenna, amplifies it to a level suitable for further processing, and finally converts through demodulation and decoding the signal into a form usable for the consumer, such as sound, pictures, digital data, measurement values, navigational positions, etc.

Radio band

{| class=wikitable style="text-align:center; font-size:11px; float:right; margin:2px" |- bgcolor= style="font-size: smaller;" | colspan=8 align=center|Light Comparison |- ! Name || Wavelength || Frequency (Hz) || Photon Energy (eV) |- | Gamma ray || less than 0.01 nm || more than 10 EHZ || 100 keV - 300+ GeV |- | X-Ray || 0.01 to 10 nm || 30 PHz - 30 EHZ || 120 eV to 120 keV |- | Ultraviolet || 10 nm - 400 nm || 30 EHZ - 790 THz || 3 eV to 124 eV |- | Visible || 390 nm - 750 nm || 790 THz - 405 THz || 1.7 eV - 3.3 eV |- | Infrared || 750 nm - 1 mm || 405 THz - 300 GHz || 1.24 meV - 1.7 eV |- | Microwave || 1 mm - 1 meter || 300 GHz - 300 MHz ||1.24 meV - 1.24 µeV |- style="background:#CCFFCC;" | Radio ||1 mm - km || 300 GHz - 3 Hz ||1.24 meV - 12.4 feV |- |}

Radio frequencies occupy the range from a few hertz to 300 GHz, although commercially important uses of radio use only a small part of this spectrum. 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.

Communication systems

A ''radio communication system'' sends signals by radio. Types of radio communication systems deployed depend on technology, standards, regulations, radio spectrum allocation, user requirements, service positioning, and investment.

The radio equipment involved in communication systems includes a transmitter and a receiver, each having an antenna and appropriate terminal equipment such as a microphone at the transmitter and a loudspeaker at the receiver in the case of a voice-communication system.

The power consumed in a transmitting station varies depending on the distance of communication and the transmission conditions. The power received at the receiving station is usually only a tiny fraction of the transmitter's output, since communication depends on receiving the information, not the energy, that was transmitted.

Classical radio communications systems use frequency-division multiplexing (FDM) as a strategy to split up and share the available radio-frequency bandwidth for use by different parties communications concurrently. Modern radio communication systems include those that divide up a radio-frequency band by time-division multiplexing (TDM) and code-division multiplexing (CDM) as alternatives to the classical FDM strategy. These systems offer different tradeoffs in supporting multiple users, beyond the FDM strategy that was ideal for broadcast radio but less so for applications such as mobile telephony.

A radio communication system may send information only one way. For example, in broadcasting a single transmitter sends signals to many receivers. Two stations may take turns sending and receiving, using a single radio frequency; this is called "simplex." By using two radio frequencies, two stations may continuously and concurrently send and receive signals - this is called "[[Duplex (telecommunications)| duplex]]" operation.

History

19th century

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 were undertaken by Thomas Edison and his employees of Menlo Park. Edison applied in 1885 to the U.S. Patent Office for a patent on an electrostatic coupling system between elevated terminals. The patent was granted as on December 29, 1891. The Marconi Company would later purchase rights to the Edison patent to protect them legally from lawsuits.

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. 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.

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). In radio transmission technology, early public experimenters had made short distance broadcasts. Marconi achieved long range signalling due to a wireless transmitting apparatus and a radio receiver claimed by him. From Marconi's experiments, the phenomenon that transmission range is proportional to the square of antenna height is known as "Marconi's law."

This formula represents a physical law that radio devices use. Marconi's experimental apparatus proved to be a complete, commercially successful radio transmission system. 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."

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.

20th century

In 1900, Brazilian priest Roberto Landell de Moura transmitted the human voice by wireless. According the newspaper ''Jornal do Comercio'' (June 10, 1900), he conducted his first public experiment on June 3, 1900, in front of journalists and the General Consul of Great Britain, C.P. Lupton, in São Paulo, Brazil, for a distance of approximately 8 km. The points of transmission and reception were Alto de Santana and Paulista Avenue.

One year after that experiment, he received his first patent from the Brazilian government. It was described as "equipment for the purpose of phonetic transmissions through space, land and water elements at a distance with or without the use of wires." Four months later, knowing that his invention had real value, he left Brazil for the United States of America with the intent of patenting the machine at the U. S. Patent Office in Washington, DC.

Having few resources, he had to rely on friends to push his project. In spite of great difficulty, three patents were awarded: "The Wave Transmitter" (October 11, 1904) which is the precursor of today's radio transceiver; "The Wireless Telephone" and the "Wireless Telegraph," both dated November 22, 1904. thumb|180px|"The Wireless Telephone" U S Patent Office in Washington, DC

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.

That month 2ADD (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 radius and later for a radius. In November 1920, it aired the first broadcast of a sporting event. At 9 pm on August 27, 1920, Sociedad Radio Argentina aired a live performance of Richard Wagner's opera ''Parsifal'' 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 college football on radio broadcast of a 1921 West Virginia vs. Pittsburgh football game.

In 1943, the United States Supreme Court invalidated one of the Marconi patents, number 763,772 (1904), on the basis it had been anticipated by Tesla, Lodge, and others. After years of patent battles by Marconi's company, the United States Supreme Court, in the 1943 case of Marconi Wireless Telegraph co. of America v. United States, 320 U.S. 1 (1943), said that "it is now held that in the important advance upon his basic patent Marconi did nothing that had not already been seen and disclosed."

Although Marconi claimed that he had no knowledge of prior art from Tesla's patents, the Supreme Court considered his claim false. In addition to that ruling from the Supreme Court, the United States Court of Claims invalidated the fundamental 1935 Marconi patent. 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." 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.

In contrast, related developments in the United Kingdom saw the High Court of Justice uphold Marconi's British Patent, issued on April 26, 1900. This patent 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 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.

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. 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. It was small enough to fit in a vest pocket, 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 high-power transmitters.

By 1963, color television was being 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 launch of the Global Positioning System (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. 2012 saw the first transmission of the Passover classic "Matzah" on Harvard's WHRB station.

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, 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 (''RA''dio ''D''etection ''A''nd ''R''anging).

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 the late 1920s 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.

Audio

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.

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 50–200 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.

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.

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.

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.

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.

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.

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.

Data (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. 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 subchannels. Modern COFDM systems use a small computer to make and decode the signal with digital signal processing, which is more flexible and far less expensive than older systems that implemented separate electronic channels.

COFDM resists fading and ghosting because the narrow-channel QAM signals can be sent slowly. An adaptive system, or one that sends error-correction codes can also resist interference, because most interference can affect only a few of the QAM channels. COFDM is used for Wi-Fi, some cell phones, Digital Radio Mondiale, Eureka 147, and many other local area network, digital TV and radio standards.

Heating

Radio-frequency energy generated for heating of objects is generally not intended to radiate outside of the generating equipment, to prevent interference with other radio signals. Microwave ovens use intense radio waves to heat food. Diathermy equipment is used in surgery for sealing of blood vessels. Induction furnaces are used for melting metal for casting, and induction hobs for cooking.

Amateur radio service

Amateur radio, also known as "ham radio," is a hobby in which enthusiasts are licensed to communicate on a number of bands in the radio frequency spectrum non-commercially and for their own enjoyment. They may also provide emergency and public service assistance. This has been very beneficial in emergencies, saving lives in many instances.

Radio amateurs use a variety of modes, including nostalgic ones like Morse code and experimental ones like Low-Frequency Experimental Radio. Several forms of radio were pioneered by radio amateurs and later became commercially important, including FM, single-sideband (SSB), AM, digital packet radio and satellite repeaters. Some amateur frequencies may be disrupted illegally by power-line internet service.

Unlicensed radio services

Unlicensed, government-authorized personal radio services such as Citizens' band radio in Australia, the USA, and Europe, and Family Radio Service and Multi-Use Radio Service in North America exist to provide simple, (usually) short range communication for individuals and small groups, without the overhead of licensing. Similar services exist in other parts of the world. These radio services involve the use of handheld units.

Free radio stations, sometimes called pirate radio or "clandestine" stations, are unauthorized, unlicensed, illegal broadcasting stations. These are often low power transmitters operated on sporadic schedules by hobbyists, community activists, or political and cultural dissidents. Some pirate stations operating offshore in parts of Europe and the United Kingdom more closely resembled legal stations, maintaining regular schedules, using high power, and selling commercial advertising time.

Radio control (RC)

Radio remote controls use radio waves to transmit control data to a remote object as in some early forms of guided missile, some early TV remotes and a range of model boats, cars and airplanes. Large industrial remote-controlled equipment such as cranes and switching locomotives now usually use digital radio techniques to ensure safety and reliability.

In Madison Square Garden, at the Electrical Exhibition of 1898, Nikola Tesla successfully demonstrated a radio-controlled boat. He was awarded U.S. patent No. 613,809 for a "Method of and Apparatus for Controlling Mechanism of Moving Vessels or Vehicles."

See also

References

;General information

''A História da Rádio em Datas (1819-1997)'' (in Portuguese) - notes on etymology

L. de Forest, article in Electrical World 22 June 1270/1 (1907), early use of word "radio."

http://web.mit.edu/varun_ag/www/bose.html - It contains a proof that Sir Jagadish Chandra Bose invented the Mercury Coherer which was later used by Guglielmo Marconi and along with other patents.

;Footnotes

Further reading

Sewall, C. H. (1904). Wireless telegraphy: its origins, development, inventions, and apparatus. New York: D. Van Nostrand.

Mills, J. (1917). Radio communication, theory and methods, with an appendix on transmission over wires. New York: McGraw-Hill book company [etc., etc.].

Lauer, H., & Brown, H. L. (1920). Radio engineering principles. New York: McGraw-Hill book company; [etc., etc.].

Cockaday, L. M. (1922). Radio-telephony for everyone; the wireless: how to construct and maintain modern transmitting and receiving apparatus. New York: Frederick A. Stokes.

Hausmann, E., Goldsmith, A. N., Hazeltine, L. A., Hogan, J. V. L., Morecroft, J. H., Canavaciol, F. E., et al. (1922). Radio phone receiving; a practical book for everybody. New York: D. Van Nostrand.

Da Silva, E. (2001). High frequency and microwave engineering. Oxford: Butterworth-Heinemann.

Hugh G. J. Aitkin: ''The Continuous Wave: Technology and the American Radio, 1900-1932'' (Princeton University Press, 1985).

Asa Briggs: ''The History of Broadcasting in the United Kingdom'' (Oxford University Press, 1961).

John Dunning: ''On the Air. The Encyclopedia of Old-Time Radio''. New York; Oxford: Oxford University Press, 1998. ISBN 0-19-507678-8

Henry Ewbank and Sherman P. Lawton: ''Broadcasting: Radio and Television'' (Harper & Brothers, 1952).

Marc Fisher: ''Something In The Air: Radio, Rock, and the Revolution That Shaped A Generation'' (Random House, 2007).

Leland I. Anderson (ed.), "John Stone Stone, Nikola Tesla's Priority in Radio and Continuous-Wave Radiofrequency Apparatus." The AWA Review, Vol. 1. 1986. 24 pages, illustrated.

Tom Lewis: ''Empire of the Air: The Men Who Made Radio'', 1st ed., New York : E. Burlingame Books, 1991. ISBN 0060182156. "Empire of the Air: The Men Who Made Radio" (1992) by Ken Burns was a PBS documentary based on the book.

W. Rupert Maclaurin: ''Invention and Innovation in the Radio Industry'' (The Macmillan Company, 1949).

William B. Ray: ''FCC: The Ups and Downs of Radio-TV Regulation'' (Iowa State University Press, 1990).

Alexander Russo: ''Points on the Dial: Golden Age Radio Beyond the Networks'' (Duke University Press; 2010) 278 pages; discusses regional and local radio as forms that "complicate" the image of the medium as a national unifier from the 1920s to the 1950s.

Scannell, Paddy, and Cardiff, David. ''A Social History of British Broadcasting, Volume One, 1922-1939'' (Basil Blackwell, 1991).

Schwoch James. ''The American Radio Industry and Its Latin American Activities, 1900-1939'' (University of Illinois Press, 1990).

Christopher H. Sterling with Michael C. Keith (ed.): ''Encyclopedia of Radio''. New York; London: Fitzroy Dearborn, 2004 (three vols.)

Llewellyn White: ''The American Radio'' (University of Chicago Press, 1947).

Ulrich L. Rohde, Jerry Whitaker: ''Communications Receivers, Third Edition'', McGraw Hill, New York, NY, 2001, ISBN 0-07-136121-9.

External links

;General

"It's Radi-O! Essay by Richard Rubin, ''The Atlantic Monthly'', January 1998.

;History

U.S. Supreme Court, "''Marconi Wireless Telegraph co. of America v. United States''." 320 U.S. 1. Nos. 369, 373. Argued 9–12 April 1943. Decided 21 June 1943.

"''Who Invented Radio?''" Buzzle.com Date unknown. retrieved 20 January 2011.

Steven Schoenherr's History of Radio

The Broadcast Archive - Radio History on the Web! Retrieved 20 January 2011.

Canadian Communications Foundation - The History on Canadian Broadcasting - 1920 onward. Retrieved 20 January 2011.

United States Early Radio History -1897 to 1927. Retrieved 20 January 2011.

Historic Radios from Around the World at Kurrajong Radio Museum, Australia - a private collection. Retrieved 20 January 2011.

;Antiques

George H. Clark Radioana Collection, ca. 1880 - 1950 - Archives Center, National Museum of American History, Smithsonian Institution

A gallery of Antiques from the 1920s to the 1960s

;Technical

Radio Frequency Chart National Telecommunications and Information Administration (NTIA).

IAteacher: Interactive Explanation of Radio Receiver Construction

How Stuff Works - Radio

VOR Basic Information

Dr. Phil's Receiver Designs Single-Triode and Single-Transistor Regenerative Radio Designs

How to design a traditional radio by Natalian Zhai, Silicon Labs

;DX

The British DX Club

World of Radio Glenn Hauser's internationally known DX radio show

Category:British inventions

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[[File:LocationWesternAfrica.png|thumb| ]]

West Africa or Western Africa is the westernmost region of the African continent. Geopolitically, the United Nations definition of Western Africa includes the following 16 countries and an area of approximately 5 million square km:

Countries of West Africa

With the exception of Mauritania, all of these countries are members of the Economic Community of West African States (ECOWAS), which was set up in May 1975. The UN region also includes the island of Saint Helena, a British overseas territory in the South Atlantic Ocean.

Background

West Africa is west of an imagined north-south axis lying close to 10° east longitude. The Atlantic Ocean forms the western as well as the southern borders of the West African region. The northern border is the Sahara Desert, with the Ranishanu Bend generally considered the northernmost part of the region. The eastern border is less precise, with some placing it at the Benue Trough, and others on a line running from Mount Cameroon to Lake Chad.

Colonial boundaries are reflected in the modern boundaries between contemporary West African nations, cutting across ethnic and cultural lines, often dividing single ethnic groups between two or more countries.

The inhabitants of West Africa are, in contrast to most of Southern and Middle Africa, non-Bantu speaking peoples.

Geography and climate

West Africa, if one includes the western portion of the Maghreb (Western Sahara, Morocco, Algeria, and Tunisia), occupies an area in excess of 6,140,000 km², or approximately one-fifth of Africa. The vast majority of this land is plains lying less than 300 meters above sea level, though isolated high points exist in numerous countries along the southern shore of the region.

The northern section of West Africa is composed of semi-arid terrain known as Sahel, a transitional zone between the Sahara and the savannahs of the western Sudan forests form a third belt between the savannas and the southern coast, ranging from 160 km to 240 km in width.

Culture

Despite the wide variety of cultures in West Africa, from Nigeria through to Senegal, there are general similarities in dress, cuisine, music and culture that are not shared extensively with groups outside the geographic region. This long history of cultural exchange predates the colonisation era of the region and can be approximately placed at the time of the Ghana Empire (proper: Wagadou Empire), Mali Empire or perhaps before such empires.

Cuisine

A large number of travellers such as traders, historians, emigrant, colonialists, missionaries, etc., have travelled the world to the West African Region and have benefited from the generosity of the native populations and left with a piece of the cultural heritage of the region. Implicitly, West African cuisines have had a significant influence on the Western World for centuries. For example a large number of West African recipes are enjoyed in the West Indies, Australia, Louisiana, Italy, Haiti, and all over the world. Although some of these recipes have been altered to suit the other climates and tastes, nevertheless they still retain their West African fervours.

West Africans cuisine includes fish especially among the coastal areas, meat, vegetables and fruits most which are grown by farmers within the region. In spite of the obvious differences among the local cuisines in the region, there are more similarities than differences. The small difference may be in the ingredients used. Most foods are boiled or fried. Starchy vegetables including yam, plantain, cassava, sweet potatoes. Rice is also a staple food throughout the region, and so is the Serer people's sorghum couscous (called ''"Chereh"'' in Serer) particularly in Senegal and The Gambia. Jolof rice originally from the Kingdom of Jolof (now part of modern day Senegal which spread to the Wolofs of Gambia), is enjoyed throughout West Africa and in the Western World; Mafé from Mali (Note: ''Mafé'' or ''Maafe'' is a Wolof word for it, the proper name is ''"Domodah"'' among the Mandinka people of Senegal and Gambia who are the originators of this dish or ''"Tigh-dege-na"'' among the Bambara people or Mandinka people of Mali, "Domodah" is also used by all Senegambians borrowed from the Mandinka language) - a peanut-butter stew served with rice; Akara (fried bean balls seasoned with spices served with sauce and bread) from Nigeria is a favourite breakfast for Gambians and Senegalese, as well as a favourite side snack or side dish in Brazil and the Caribbean just as it is in West Africa. It is said that its exact origin may be from Yorubaland in Nigeria. Fufu (from the Twi language, a dough served with a spicy stew or sauce for example okra stew etc.) from Ghana is enjoyed throughout the region and beyond even in Central Africa with their own versions of it.

Recreation

The board game oware is quite popular in many parts of West Africa. The word ''"Oware"'' originates from the Akan people of Ghana. However, virtually all African peoples have a version of this board game. football is also a pastime enjoyed by many, either spectating or playing. The national teams of some West African nations, especially Nigeria, Ghana and the Ivory Coast regularly qualify for the World Cup.

Music

Mbalax, Highlife, Fuji and Afrobeat are all modern musical genres which listeners enjoy in this region. Old traditional folk music is also well preserved in this region. Some of these are religious in nature such as the "Tassou" tradition used in Serer religion.

Griot tradition

Traditionally, musical and oral history as conveyed over generations by Griots are typical of West African culture.

Clothing

A typical formal attire worn in this region are the knee to ankle-length flowing Boubou robe, Dashiki and Senegalese Kaftan (also known as ''Agbada'' and ''Babariga''), which has its origins in the clothing of nobility of various West African empires in the 12th century.

Film industry

Nollywood of Nigeria, is the main film industry of West Africa. The Nigerian cinema industry is the second largest film industry in the world in terms of annual film production, even ahead of the United States's Hollywood film industry. Senegal and Ghana also has long traditions of producing films. The late Ousmane Sembène, the Senegalese film director, producer and writer is from the region, as is the Ghanaian Shirley Frimpong-Manso.

Religion

Islam

Islam is the predominant religion of the West African interior and the far west coast of the continent. Traditional Muslim areas include parts of Senegal, Gambia, Mali, Guinea , Niger; the inland areas of Sierra Leone and Liberia; the western, northern and far-eastern regions of Burkina Faso; and the northern halves of the coastal nations of Cameroon, Nigeria, Benin, Togo, Ghana and Cote d'Ivoire.

Christianity

Christianity, a relative newcomer, has become the predominant religion in the central and southern part of Nigeria, and the coastal regions stretching from southern Ghana to coastal parts of Sierra Leone. Like Islam, elements of Traditional African religion are mixed with Christianity. This religion was brought to the region by European missionaries during the colonial era.

African traditional

thumb|left|150px|Voodoo altar with several fetishes in Abomey, BeninTraditional African religion is the oldest and original religion of the native populations of this region, and includes Yoruba religion, Odinani, Serer religion, etc. It is spiritual but also linked to the historical and cultural heritage of the people. Before the arrival of other religions such as Islam and Christianity, West Africans, like most Africans, had a well-developed system of religious beliefs. The Traditional African religion is still practiced by the native populations. Although traditional beliefs varies from one place to the next, there are more similarities than differences. This belief system is a major religion of Benin.

History

The history of West Africa can be divided into five major periods: first, its prehistory, in which the first human settlers arrived, developed agriculture, and made contact with peoples to the north; the second, the Iron Age empires that consolidated both intra-African, and extra-African trade, and developed centralized states; third, Major polities flourished, which would undergo an extensive history of contact with non-Africans; fourth, the colonial period, in which Great Britain and France controlled nearly the whole of the region; fifth, the post-independence era, in which the current nations were formed.

Prehistory

Early human settlers arrived in West Africa around 12,000 B.C. Sedentary farming began in, or around the fifth millennium B.C, as well as the domestication of cattle. By 400 B.C, ironworking technology allowed an expansion of agricultural productivity, and the first city-states formed.

The domestication of the camel allowed the development of a cross-Saharan trade with cultures across the Sahara, including Carthage and the Berbers; major exports included gold, cotton cloth, metal ornaments and leather goods, which were then exchanged for salt, horses, textiles, and other such materials. Local leather, cloth, and gold also contributed to the abundancy of prosperity for many of the following empires.

Empires

The development of the region's economy allowed more centralized states and civilizations to form, beginning with the Nok culture which began 1000 B.C. and the Ghana Empire which first flourished between the 1st-3rd centuries which later gave way to the Mali empire. In current day Mauritania, there exists archaeological sites in the towns of Tichit and Oualata that were initially constructed around 2000 B.C., and was found to have originated from the Soninke branch of the Mandé peoples. Also, based on the archaeology of city of Kumbi Saleh in modern-day Mauritania, the Mali empire came to dominate much of the region until its defeat by Almoravid invaders in 1052.

The Sosso Empire sought to fill the void, but was defeated (c. 1240) by the Mandinka forces of Sundiata Keita, founder of the new Mali Empire. The Mali Empire continued to flourish for several centuries, most particularly under Sundiata's grandnephew) Musa I, before a succession of weak rulers led to its collapse under Mossi, Tuareg and Songhai invaders. In the 15th century, the Songhai would form a new dominant state based on Gao, in the Songhai Empire, under the leadership of Sonni Ali and Askia Mohammed.

Meanwhile, south of the Sudan, strong city states arose in Igboland, such as the Kingdom of Nri in the 10th century, Bono in the 12th century which eventually culminated in the formation the all-powerful Akan Empire of Ashanti, while Ife and Benin rose to prominence around the 14th century. Further east, Oyo arose as the dominant Yoruba state and the Aro Confederacy as a dominant Igbo state in modern-day Nigeria.

Slavery and European contact

Portuguese traders began establishing settlements along the coast in 1445, followed by the French and English; the African slave trade began not long after, which over the following centuries would debilitate the region's economy and population. The slave trade also encouraged the formation of states such as the Asante Empire, Bambara Empire and Dahomey, whose economic activities include but not limited to exchanging slaves for European firearms.

Colonialism

In the early 19th century, a series of Fulani reformist jihads swept across Western Africa. The most notable include Usman dan Fodio's Fulani Empire, which replaced the Hausa city-states, Seku Amadu's Massina Empire, which defeated the Bambara, and El Hadj Umar Tall's Toucouleur Empire, which briefly conquered much of modern-day Mali.

However, the French and British continued to advance in the Scramble for Africa, subjugating kingdom after kingdom. With the fall of Samory Ture's new-founded Wassoulou Empire in 1898 and the Ashanti queen Yaa Asantewaa in 1902, most West African military resistance to colonial rule came to an effective end.

Britain controlled The Gambia, Sierra Leone, Ghana, and Nigeria throughout the colonial era, while France unified Senegal, Guinea, Mali, Burkina Faso, Benin, Côte d'Ivoire and Niger into French West Africa. Portugal founded the colony of Guinea-Bissau, while Germany claimed Togoland, but was forced to divide it between France and Britain following First World War due to the Treaty of Versailles. Only Liberia retained its independence, at the price of major territorial concessions.

Postcolonial era

Following World War II, nationalist movements arose across West Africa. In 1957, Ghana, under Kwame Nkrumah, became the first sub-Saharan colony to achieve its independence, followed the next year by France's colonies (Guinea in 1958 under the leadership of President Ahmed Sekou Touré); by 1974, West Africa's nations were entirely autonomous.

Since independence, many West African nations have been submerged under political instability, with notable civil wars in Nigeria, Sierra Leone, Liberia, and Côte d'Ivoire, and a succession of military coups in Ghana and Burkina Faso.

Since the end of colonialism, the region has been the stage for some of the most brutal conflicts ever to erupt. Among the latter are:

Nigerian Civil War

First Liberian Civil War

Second Liberian Civil War

Guinea-Bissau Civil War

Ivorian Civil War

Sierra Leone Civil War

Regional organizations

The Economic Community of West African States (ECOWAS), founded by the 1975 Treaty of Lagos, is an organization of West African states which aims to promote the region's economy. The West African Monetary Union (or UEMOA from its name in French, ''Union économique et monétaire ouest-africaine'') is limited to the eight, mostly Francophone countries that employ the CFA franc as their common currency. The Liptako-Gourma Authority of Mali, Niger, and Burkina Faso seeks to jointly develop the contiguous areas of the three countries.

Women's peace movement

Since the adoption of the United Nations Security Council Resolution 1325 in 2000, women have been engaged in rebuilding war-torn Africa. Starting with the Women of Liberia Mass Action for Peace and ''Women in Peacebuilding Network (WIPNET),'' the peace movement has grown to include women across West Africa.

Established on May 8, 2006, ''Women Peace and Security Network - Africa'' (WIPSEN-Africa), is a women-focused, women-led Pan-African non-governmental organization based in Ghana. The organization has a presence in Ghana, Nigeria, Cote d’Ivoire, Liberia and Sierra Leone. Regional leaders of nonviolent resistance include Leymah Gbowee, Comfort Freeman, and Aya Virginie Toure.

''Pray the Devil Back to Hell'' is a documentary film about the origin of this peace movement. The film has been used as an advocacy tool in post-conflict zones like Sudan and Zimbabwe, mobilizing African women to petition for peace and security.

See also

Empires

Ghana Empire

Mali Empire

Empire of Ashanti

Songhai Empire

Heritage

World Heritage Site

Natural disaster

2004 locust outbreak

Monetary unit

Manillas – A form of archaic money unique to West Africa

Script

Nsibidi Script - An indigenously developed West African writing system

Vai syllabary

Sailors

Seedies and Kroomen

Disputed territory

Western Sahara

References

External links

5 West African Holidays

''West Africa by Region and Country'' – African Studies at Columbia University

ouestaf.com – Online source for news and current affairs in west Africa.

- The loss of Togo in result in World War 1

Loccidental – The News reference for West Africa.

West Africa Review – An e-journal on West Africa research and scholarship.

West African Plants Database – photos and plant identification

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