A communications satellite is an artificial satellite that relays and amplifies radio telecommunications signals via a transponder. Communications satellites are used for television, radio and military applications. There are 2,134 communications satellites in Earth’s orbit, used by both private and government organizations. Many are in geostationary orbit 22,200 miles above the equator, so that the satellite appears stationary at the same point in the sky, so the satellite dish antennas of ground stations can be aimed permanently at that spot and do not have to move to track it; the high frequency radio waves used for telecommunications links travel by line of sight and so are obstructed by the curve of the Earth. The purpose of communications satellites is to relay the signal around the curve of the Earth allowing communication between separated geographical points. Communications satellites use a wide range of microwave frequencies. To avoid signal interference, international organizations have regulations for which frequency ranges or "bands" certain organizations are allowed to use.
This allocation of bands minimizes the risk of signal interference. The concept of the geostationary communications satellite was first proposed by Arthur C. Clarke, along with Vahid K. Sanadi building on work by Konstantin Tsiolkovsky. In October 1945 Clarke published an article titled "Extraterrestrial Relays" in the British magazine Wireless World; the article described the fundamentals behind the deployment of artificial satellites in geostationary orbits for the purpose of relaying radio signals. Thus, Arthur C. Clarke is quoted as being the inventor of the communications satellite and the term'Clarke Belt' employed as a description of the orbit. Decades a project named Communication Moon Relay was a telecommunication project carried out by the United States Navy, its objective was to develop a secure and reliable method of wireless communication by using the Moon as a passive reflector and a natural communications satellite. The first artificial Earth satellite was Sputnik 1. Put into orbit by the Soviet Union on October 4, 1957, it was equipped with an on-board radio-transmitter that worked on two frequencies: 20.005 and 40.002 MHz.
Sputnik 1 was launched as a major step in the exploration of rocket development. However, it was not placed in orbit for the purpose of sending data from one point on earth to another; the first satellite to relay communications was an intended lunar probe. Though the spacecraft only made it about halfway to the moon, it flew high enough to carry out the proof of concept relay of telemetry across the world, first from Cape Canaveral to Manchester, England; the first satellite purpose-built to relay communications was NASA's Project SCORE in 1958, which used a tape recorder to store and forward voice messages. It was used to send a Christmas greeting to the world from U. S. President Dwight D. Eisenhower. Courier 1B, built by Philco, launched in 1960, was the world's first active repeater satellite; the first artificial satellite used to further advances in global communications was a balloon named Echo 1. Echo 1 was the world's first artificial communications satellite capable of relaying signals to other points on Earth.
It soared 1,600 kilometres above the planet after its Aug. 12, 1960 launch, yet relied on humanity's oldest flight technology — ballooning. Launched by NASA, Echo 1 was a 30-metre aluminized PET film balloon that served as a passive reflector for radio communications; the world's first inflatable satellite — or "satelloon", as they were informally known — helped lay the foundation of today's satellite communications. The idea behind a communications satellite is simple: Send data up into space and beam it back down to another spot on the globe. Echo 1 accomplished this by serving as an enormous mirror, 10 stories tall, that could be used to reflect communications signals. There are two major classes of communications satellites and active. Passive satellites only reflect the signal coming from the source, toward the direction of the receiver. With passive satellites, the reflected signal is not amplified at the satellite, only a small amount of the transmitted energy reaches the receiver. Since the satellite is so far above Earth, the radio signal is attenuated due to free-space path loss, so the signal received on Earth is very weak.
Active satellites, on the other hand, amplify the received signal before retransmitting it to the receiver on the ground. Passive satellites are little used now. Telstar was the second direct relay communications satellite. Belonging to AT&T as part of a multi-national agreement between AT&T, Bell Telephone Laboratories, NASA, the British General Post Office, the French National PTT to develop satellite communications, it was launched by NASA from Cape Canaveral on July 10, 1962, in the first sponsored space launch. Relay 1 was launched on December 13, 1962, it became the first satellite to transmit across the Pacific Ocean on November 22, 1963. An immediate antecedent of the geostationary satellites was the Hughes Aircraft Company's Syncom 2, launched on July 26, 1963. Syncom 2 was the first communications satellite in a geosynchronous orbit, it revolved around the earth once per day at constant speed, but because it still had north-south motion, special equipment was needed to track it. Its successor, Syncom 3 was the first geostationary communications satellite.
Syncom 3 obt
Broadcasting is the distribution of audio or video content to a dispersed audience via any electronic mass communications medium, but one using the electromagnetic spectrum, in a one-to-many model. Broadcasting began with AM radio, which came into popular use around 1920 with the spread of vacuum tube radio transmitters and receivers. Before this, all forms of electronic communication were one-to-one, with the message intended for a single recipient; the term broadcasting evolved from its use as the agricultural method of sowing seeds in a field by casting them broadly about. It was adopted for describing the widespread distribution of information by printed materials or by telegraph. Examples applying it to "one-to-many" radio transmissions of an individual station to multiple listeners appeared as early as 1898. Over the air broadcasting is associated with radio and television, though in recent years, both radio and television transmissions have begun to be distributed by cable; the receiving parties may include the general public or a small subset.
The field of broadcasting includes both government-managed services such as public radio, community radio and public television, private commercial radio and commercial television. The U. S. Code of Federal Regulations, title 47, part 97 defines "broadcasting" as "transmissions intended for reception by the general public, either direct or relayed". Private or two-way telecommunications transmissions do not qualify under this definition. For example and citizens band radio operators are not allowed to broadcast; as defined, "transmitting" and "broadcasting" are not the same. Transmission of radio and television programs from a radio or television station to home receivers by radio waves is referred to as "over the air" or terrestrial broadcasting and in most countries requires a broadcasting license. Transmissions using a wire or cable, like cable television, are considered broadcasts but do not require a license. In the 2000s, transmissions of television and radio programs via streaming digital technology have been referred to as broadcasting as well.
The earliest broadcasting consisted of sending telegraph signals over the airwaves, using Morse code, a system developed in the 1830s by Samuel F. B. Morse, physicist Joseph Henry and Alfred Vail, they developed an electrical telegraph system which sent pulses of electric current along wires which controlled an electromagnet, located at the receiving end of the telegraph system. A code was needed to transmit natural language using only these pulses, the silence between them. Morse therefore developed the forerunner to modern International Morse code; this was important for ship-to-ship and ship-to-shore communication, but it became important for business and general news reporting, as an arena for personal communication by radio amateurs. Audio broadcasting began experimentally in the first decade of the 20th century. By the early 1920s radio broadcasting became a household medium, at first on the AM band and on FM. Television broadcasting started experimentally in the 1920s and became widespread after World War II, using VHF and UHF spectrum.
Satellite broadcasting was initiated in the 1960s and moved into general industry usage in the 1970s, with DBS emerging in the 1980s. All broadcasting was composed of analog signals using analog transmission techniques but in the 2000s, broadcasters have switched to digital signals using digital transmission. In general usage, broadcasting most refers to the transmission of information and entertainment programming from various sources to the general public. Analog audio vs. HD Radio Analog television vs. Digital television WirelessThe world's technological capacity to receive information through one-way broadcast networks more than quadrupled during the two decades from 1986 to 2007, from 432 exabytes of information, to 1.9 zettabytes. This is the information equivalent of 55 newspapers per person per day in 1986, 175 newspapers per person per day by 2007. There have been several methods used for broadcasting electronic media audio and video to the general public: Telephone broadcasting: the earliest form of electronic broadcasting.
Telephone broadcasting began with the advent of Théâtrophone systems, which were telephone-based distribution systems allowing subscribers to listen to live opera and theatre performances over telephone lines, created by French inventor Clément Ader in 1881. Telephone broadcasting grew to include telephone newspaper services for news and entertainment programming which were introduced in the 1890s located in large European cities; these telephone-based subscription services were the first examples of electrical/electronic broadcasting and offered a wide variety of programming. Radio broadcasting. Radio stations can be linked in radio networks to broadcast common radio programs, either in broadcast syndication, simulcast or subchannels. Television broadcasting, experimentally from 1925, commercially from t
Territories of the United States
Territories of the United States are sub-national administrative divisions overseen by the federal government. They differ from U. S. Native American tribes, which have limited sovereignty; the territories are classified by incorporation and whether they have an "organized" government through an organic act passed by Congress. The U. S. has sixteen territories in the Caribbean Sea and the Pacific Ocean. Five are permanently-inhabited, unincorporated territories. Of the eleven, only one is classified as an incorporated territory. Two territories are defacto administered by Colombia. Territories were created to administer newly-acquired land, most attained statehood. Others, such as the Philippines, the Marshall Islands and Palau became independent. Many organized incorporated territories of the United States existed from 1789 to 1959; the first were the Northwest and Southwest territories, the last were the Alaska and Hawaii Territories. Thirty-one territories became states. In the process, some less-developed or -populous areas of a territory were orphaned from it after a statehood referendum.
When a portion of the Missouri Territory became the state of Missouri, the remainder of the territory became an unorganized territory. Territorial telecommunications and other infrastructure is inferior to that of the U. S. mainland, American Samoa's Internet speed was found to be slower than several Eastern European countries. Poverty rates are higher in the territories than in the states; the U. S. has had territories since its beginning. According to federal law, the term "United States" means "the continental United States, Puerto Rico and the United States Virgin Islands". Since 1986, the Northern Mariana Islands have been considered part of the U. S. A 2007 executive order included American Samoa in the U. S. "geographical extent", as reflected in the Federal Register. All territories are except for American Samoa and Jarvis Island; the U. S. has five permanently-inhabited territories, two of which are known as "commonwealths": Puerto Rico and the U. S. Virgin Islands in the Caribbean Sea. About four million people in these territories are U.
S. citizens, citizenship at birth is granted in four of the five territories. American Samoa has about 32,000 non-citizen U. S. nationals. Under U. S. law, "only persons born in American Samoa and Swains Island are non-citizen U. S. nationals" in its territories. American Samoans are under U. S. protection, can travel to the rest of the U. S. without a visa. American Samoans must become naturalized citizens, like foreigners. Unlike the other four inhabited territories, Congress has passed no legislation granting birthright citizenship to American Samoans; each territory is self-governing with three branches of government, including a locally-elected governor and a territorial legislature. It elects a non-voting member to the U. S. House of Representatives, they "possess the same powers as other members of the House, except that they may not vote when the House is meeting as the House of Representatives". They can vote in their appointed House committees on all legislation presented to the House, they are included in their party count for each committee, they are equal to senators on conference committees.
Depending on the Congress, they may vote on the floor in the House Committee of the Whole. In January 2017, the members of Congress from the territories were Gregorio Sablan, Madeleine Bordallo, Amata Coleman Radewagen, Jenniffer González and Stacey Plaskett; the District of Columbia has a non-voting delegate. Like the District of Columbia, U. S. territories do not have voting representation in Congress and have no representation in the Senate. Every four years, U. S. political parties nominate presidential candidates at conventions which include delegates from the territories. U. S. citizens living in the territories cannot vote in the general presidential election, non-citizen nationals in American Samoa cannot vote for president. The territorial capitals are Pago Pago, Hagåtña, San Juan and Charlotte Amalie, their governors are Lolo Matalasi Moliga, Eddie Baza Calvo, Ralph Torres, Ricardo Rosselló and Kenneth Mapp. American Samoa – Territory since 1900; the U. S. controlled the eastern half of the islands.
In 1900, the Treaty of Cession of Tutuila took effect. The Manuʻa islands became part of American Samoa in 1904, Swains Island became part of American Samoa in 1925. Congress ratified American Samoa's treaties in 1929. American Samoa is locally self-governing under a constitution last revised in 1967. People born in American Samoa are U. S. nationals. A
Guam is an unincorporated and organized territory of the United States in Micronesia in the western Pacific Ocean. It is the easternmost point and territory of the United States, along with the Northern Mariana Islands; the capital city of Guam is Hagåtña and the most populous city is Dededo. The inhabitants of Guam are called Guamanians, they are American citizens by birth. Indigenous Guamanians are the Chamorros, who are related to other Austronesian natives of Eastern Indonesia, the Philippines, Taiwan. Guam has been a member of the Pacific Community since 1983. In 2016, 162,742 people resided on Guam. Guam has a population density of 775 per square mile. In Oceania, it is the largest and southernmost of the Mariana Islands and the largest island in Micronesia. Among its municipalities, Mongmong-Toto-Maite has the highest population density at 3,691 per square mile, whereas Inarajan and Umatac have the lowest density at 119 per square mile; the highest point is Mount Lamlam at 1,332 feet above sea level.
Since the 1960s, the economy has been supported by two industries: tourism and the United States Armed Forces. The indigenous Chamorros settled the island 4,000 years ago. Portuguese explorer Ferdinand Magellan, while in the service of Spain, was the first European to visit the island, on March 6, 1521. Guam was colonized by Spain in 1668 with settlers, including Diego Luis de San Vitores, a Catholic Jesuit missionary. Between the 16th century and the 18th century, Guam was an important stopover for the Spanish Manila Galleons. During the Spanish–American War, the United States captured Guam on June 21, 1898. Under the Treaty of Paris, Spain ceded Guam to the United States on December 10, 1898. Guam is among the 17 non-self-governing territories listed by the United Nations. Before World War II, there were five American jurisdictions in the Pacific Ocean: Guam and Wake Island in Micronesia, American Samoa and Hawaii in Polynesia, the Philippines. On December 7, 1941, hours after the attack on Pearl Harbor, Guam was captured by the Japanese, who occupied the island for two and a half years.
During the occupation, Guamanians were subjected to beheadings, forced labor and torture. American forces recaptured the island on July 21, 1944. An unofficial but used territorial motto is "Where America's Day Begins", which refers to the island's close proximity to the international date line; the original inhabitants of Guam and the Northern Mariana Islands were the Chamorro people, who are believed to be descendants of Austronesian people originating from Southeast Asia as early as 2000 BC. The ancient Chamorro society had four classes: chamorri, matua and mana'chang; the matua were located in the coastal villages, which meant they had the best access to fishing grounds, whereas the mana'chang were located in the interior of the island. Matua and mana'chang communicated with each other, matua used achaot as intermediaries. There were "makåhna" or "kakahna", shamans with magical powers and "Suruhånu" or "Suruhåna" healers who use different kinds of plants and natural materials to make medicine.
Belief in spirits of ancient Chamorros called "Taotao mo'na" still persists as a remnant of pre-European culture. It is believed that "Suruhånu" or "Suruhåna" are the only ones who can safely harvest plants and other natural materials from their homes or "hålomtåno" without incurring the wrath of the "Taotao mo'na", their society was organized along matrilineal clans. Latte stones are stone pillars; the latte-stone was used as a foundation. Latte stones consist of a base shaped from limestone called the haligi and with a capstone, or tåsa, made either from a large brain coral or limestone, placed on top. A possible source for these stones, the Rota Latte Stone Quarry, was discovered in 1925 on Rota; the first European to travel to Guam was Portuguese navigator Ferdinand Magellan, sailing for the King of Spain, when he sighted the island on March 6, 1521, during his fleet's circumnavigation of the globe. When Magellan arrived on Guam, he was greeted by hundreds of small outrigger canoes that appeared to be flying over the water, due to their considerable speed.
These outrigger canoes were called Proas, resulted in Magellan naming Guam Islas de las Velas Latinas. Antonio Pigafetta said that the name was "Island of Sails", but he writes that the inhabitants "entered the ships and stole whatever they could lay their hands on", including "the small boat, fastened to the poop of the flagship." "Those people are poor, but ingenious and thievish, on account of which we called those three islands Islas de los Ladrones." Despite Magellan's visit, Guam was not claimed by Spain until January 26, 1565, by General Miguel López de Legazpi. From 1565 to 1815, Guam and the Northern Mariana Islands, the only Spanish outposts in the Pacific Ocean east of the Philippines, were an important resting stop for the Manila galleons, a fleet that covered the Pacific trade route between Acapulco and Manila. To protect these Pacific fleets, Spain built several defensive structures that still stand today, such as Fort Nuestra Señora de la Soledad in Umatac. Guam is the biggest single segment of Micronesia, the largest islands between the island of Kyushu, New Guinea, the Philippines, the Hawaiian Islands.
Spanish colonization commenced on June 15, 1
History of mobile phones
The history of mobile phones covers mobile communication devices that connect wirelessly to the public switched telephone network. While the transmission of speech by radio has a long history, the first devices that were wireless and capable of connecting to the standard telephone network are much more recent; the first such devices were portable compared to today's compact hand-held devices, their use was clumsy. Along with the process of developing a more portable technology, a better interconnections system, drastic changes have taken place in both the networking of wireless communication and the prevalence of its use, with smartphones becoming common globally and a growing proportion of Internet access now done via mobile broadband. Before the devices existed that are now referred to as mobile phones or cell phones, there were some precursors. In 1908, a Professor Albert Jahnke and the Oakland Transcontinental Aerial Telephone and Power Company claimed to have developed a wireless telephone.
They were accused of fraud and the charge was dropped, but they do not seem to have proceeded with production. Beginning in 1918, the German railroad system tested wireless telephony on military trains between Berlin and Zossen. In 1924, public trials started with telephone connection on trains between Hamburg. In 1925, the company Zugtelephonie AG was founded to supply train telephony equipment and, in 1926, telephone service in trains of the Deutsche Reichsbahn and the German mail service on the route between Hamburg and Berlin was approved and offered to first-class travelers. Fiction anticipated the development of real world mobile telephones. In 1906, the English caricaturist Lewis Baumer published a cartoon in Punch magazine entitled "Forecasts for 1907" in which he showed a man and a woman in London's Hyde Park each separately engaged in gambling and dating on wireless telephony equipment. In 1926, the artist Karl Arnold created a visionary cartoon about the use of mobile phones in the street, in the picture "wireless telephony", published in the German satirical magazine Simplicissimus.
The Second World War made military use of radio telephony links. Hand-held radio transceivers have been available since the 1940s. Mobile telephones for automobiles became available from some telephone companies in the 1940s. Early devices were bulky, consumed large amounts of power, the network supported only a few simultaneous conversations. Modern cellular networks allow automatic and pervasive use of mobile phones for voice and data communications. In the United States, engineers from Bell Labs began work on a system to allow mobile users to place and receive telephone calls from automobiles, leading to the inauguration of mobile service on June 17th 1946 in St. Louis, Missouri. Shortly after, AT&T offered Mobile Telephone Service. A wide range of incompatible mobile telephone services offered limited coverage area and only a few available channels in urban areas; the introduction of cellular technology, which allowed re-use of frequencies many times in small adjacent areas covered by low powered transmitters, made widespread adoption of mobile telephones economically feasible.
In the USSR, Leonid Kupriyanovich, an engineer from Moscow, in 1957-1961 developed and presented a number of experimental pocket-sized communications radio. The weight of one model, presented in 1961, could fit on a palm. However, in the USSR the decision at first to develop the system of the automobile "Altai" phone was made. In 1965, the Bulgarian company "Radioelektronika" presented a mobile automatic phone combined with a base station at the Inforga-65 international exhibition in Moscow. Solutions of this phone were based on a system developed by Leonid Kupriyanovich. One base station, connected to one telephone wire line, could serve up to 15 customers; the advances in mobile telephony can be traced in successive generations from the early "0G" services like MTS and its successor Improved Mobile Telephone Service, to first-generation analog cellular network, second-generation digital cellular networks, third-generation broadband data services to the state-of-the-art, fourth-generation native-IP networks.
In 1949, AT&T commercialized Mobile Telephone Service. From its start in St. Louis, Missouri, in 1946, AT&T introduced Mobile Telephone Service to one hundred towns and highway corridors by 1948. Mobile Telephone Service was a rarity with only 5,000 customers placing about 30,000 calls each week. Calls were set up manually by an operator and the user had to depress a button on the handset to talk and release the button to listen; the call subscriber equipment weighed about 80 pounds Subscriber growth and revenue generation were hampered by the constraints of the technology. Because only three radio channels were available, only three customers in any given city could make mobile telephone calls at one time. Mobile Telephone Service was expensive, costing US$15 per month, plus $0.30–0.40 per local call, equivalent to about $176 per month and $3.50–4.75 per call. In the UK, there was a vehicle-based system called "Post Office Radiophone Service,", launched around the city of Manchester in 1959, although it required callers to speak to an operator, it was possible to be put through to any subscriber in Great Britain.
The service was extended to London in 1965 and other major cities in 1972. AT&T introduced the first major improvement to mobile telephony in 1965, giving the improved service the obvious name of Improved Mobile Telephone Service. IMTS used additional radio channels, allowing more simultaneous calls in a given geographic area, introduced customer dialing, eliminating manual call setup by an operator, reduced the size and weight of the subscriber equipment. Desp
A heliograph is a wireless telegraph that signals by flashes of sunlight reflected by a mirror. The flashes are produced by momentarily pivoting the mirror, or by interrupting the beam with a shutter; the heliograph was a simple but effective instrument for instantaneous optical communication over long distances during the late 19th and early 20th century. Its main uses were military and forest protection work. Heliographs were standard issue in the British and Australian armies until the 1960s, were used by the Pakistani army as late as 1975. There were many heliograph types. Most heliographs were variants of the British Army Mance Mark V version, it used a mirror with a small unsilvered spot in the centre. The sender aligned the heliograph to the target by looking at the reflected target in the mirror and moving their head until the target was hidden by the unsilvered spot. Keeping their head still, they adjusted the aiming rod so its cross wires bisected the target, they turned up the sighting vane, which covered the cross wires with a diagram of a cross, aligned the mirror with the tangent and elevation screws so the small shadow, the reflection of the unsilvered spot hole was on the cross target.
This indicated. The flashes were produced by a keying mechanism that tilted the mirror up a few degrees at the push of a lever at the back of the instrument. If the sun was in front of the sender, its rays were reflected directly from this mirror to the receiving station. If the sun was behind the sender, the sighting rod was replaced by a second mirror, to capture the sunlight from the main mirror and reflect it to the receiving station; the U. S. Signal Corps heliograph mirror did not tilt; this type produced flashes by a shutter mounted on a second tripod. The heliograph had some great advantages, it allowed long distance communication without a fixed infrastructure, though it could be linked to make a fixed network extending for hundreds of miles, as in the fort-to-fort network used for the Geronimo campaign. It was portable, did not require any power source, was secure since it was invisible to those not near the axis of operation, the beam was narrow, spreading only 50 feet per mile of range.
However, anyone in the beam with the correct knowledge could intercept signals without being detected. In the Boer War, where both sides used heliographs, tubes were sometimes used to decrease the dispersion of the beam. In some other circumstances, though, a narrow beam made it difficult to stay aligned with a moving target, as when communicating from shore to a moving ship, so the British issued a dispersing lens to broaden the heliograph beam from its natural diameter of 0.5 degrees to 15 degrees. The distance that heliograph signals could be seen depended on the clarity of the sky and the size of the mirrors used. A clear line of sight was required, since the Earth's surface is curved, the highest convenient points were used. Under ordinary conditions, a flash could be seen 30 miles with the naked eye, much farther with a telescope; the maximum range was considered to be 10 miles for each inch of mirror diameter. Mirrors ranged from 1.5 inches to 12 inches or more. The record distance was established by a detachment of U.
S. signal sergeants by the inter-operation of stations on Mount Ellen and Mount Uncompahgre, Colorado, 183 miles apart on September 17, 1894, with Signal Corps heliographs carrying mirrors only 8 inches square. The German professor Carl Friedrich Gauss of the University of Göttingen developed and used a predecessor of the heliograph in 1821, his device directed a controlled beam of sunlight to a distant station to be used as a marker for geodetic survey work, was suggested as a means of telegraphic communications. This is the first reliably documented heliographic device, despite much speculation about possible ancient incidents of sun-flash signalling, the documented existence of other forms of ancient optical telegraphy. For example, one author in 1919 chose to "hazard the theory" that the mainland signals Roman emperor Tiberius watched for from Capri were mirror flashes, but admitted "there are no references in ancient writings to the use of signaling by mirrors", that the documented means of ancient long-range visual telecommunications was by beacon fires and beacon smoke, not mirrors.
The story that a shield was used as a heliograph at the Battle of Marathon is a modern myth, originating in the 1800s. Herodotus never mentioned any flash. What Herodotus did write was that someone was accused of having arranged to "hold up a shield as a signal". Suspicion grew in the 1900s; the conclusion after testing the theory was "Nobody flashed a shield at the Battle of Marathon". In a letter dated 3 June 1778, John Norris, High Sheriff of Buckinghamshire, notes: "Did this day heliograph intelligence from Dr Franklin in Paris to Wycombe". However, there is little evidence that "heliograph" here is other than a misspelling of "holograph"; the term "heliograph" for solar telegraphy did not enter the English language until the 1870s—even the word "telegraphy" was not coined until the 1790s. Henry Christopher Mance, of the British Government Persian Gulf Telegraph Department, developed the first accepted heliograph about 1869 while stationed at Karachi, in the Bombay Presidency in British India.
Mance was familiar with heliotropes by their use for the Great India Survey. The Mance Heliograph was operated by one man, since it weighed about seven pounds, the operator could carry the devi
FM broadcasting is a method of radio broadcasting using frequency modulation technology. Invented in 1933 by American engineer Edwin Armstrong, wide-band FM is used worldwide to provide high-fidelity sound over broadcast radio. FM broadcasting is capable of better sound quality than AM broadcasting, the chief competing radio broadcasting technology, so it is used for most music broadcasts. Theoretically wideband AM can offer good sound quality, provided the reception conditions are ideal. FM radio stations use the VHF frequencies; the term "FM band" describes the frequency band in a given country, dedicated to FM broadcasting. Throughout the world, the FM broadcast band falls within the VHF part of the radio spectrum. 87.5 to 108.0 MHz is used, or some portion thereof, with few exceptions: In the former Soviet republics, some former Eastern Bloc countries, the older 65.8–74 MHz band is used. Assigned frequencies are at intervals of 30 kHz; this band, sometimes referred to as the OIRT band, is being phased out in many countries.
In those countries the 87.5–108.0 MHz band is referred to as the CCIR band. In Japan, the band 76–95 MHz is used; the frequency of an FM broadcast station is an exact multiple of 100 kHz. In most of South Korea, the Americas, the Philippines and the Caribbean, only odd multiples are used. In some parts of Europe and Africa, only multiples are used. In the UK odd or are used. In Italy, multiples of 50 kHz are used. In most countries the maximum permitted frequency error is specified, the unmodulated carrier should be within 2000 Hz of the assigned frequency. There are other unusual and obsolete FM broadcasting standards in some countries, including 1, 10, 30, 74, 500, 300 kHz. However, to minimise inter-channel interference, stations operating from the same or geographically close transmitter sites tend to keep to at least a 500 kHz frequency separation when closer frequency spacing is technically permitted, with closer tunings reserved for more distantly spaced transmitters, as interfering signals are more attenuated and so have less effect on neighboring frequencies.
Frequency modulation or FM is a form of modulation which conveys information by varying the frequency of a carrier wave. With FM, frequency deviation from the assigned carrier frequency at any instant is directly proportional to the amplitude of the input signal, determining the instantaneous frequency of the transmitted signal; because transmitted FM signals use more bandwidth than AM signals, this form of modulation is used with the higher frequencies used by TV, the FM broadcast band, land mobile radio systems. The maximum frequency deviation of the carrier is specified and regulated by the licensing authorities in each country. For a stereo broadcast, the maximum permitted carrier deviation is invariably ±75 kHz, although a little higher is permitted in the United States when SCA systems are used. For a monophonic broadcast, again the most common permitted. However, some countries specify a lower value for monophonic broadcasts, such as ±50 kHz. Random noise has a triangular spectral distribution in an FM system, with the effect that noise occurs predominantly at the highest audio frequencies within the baseband.
This can be offset, to a limited extent, by boosting the high frequencies before transmission and reducing them by a corresponding amount in the receiver. Reducing the high audio frequencies in the receiver reduces the high-frequency noise; these processes of boosting and reducing certain frequencies are known as pre-emphasis and de-emphasis, respectively. The amount of pre-emphasis and de-emphasis used is defined by the time constant of a simple RC filter circuit. In most of the world a 50 µs time constant is used. In the Americas and South Korea, 75 µs is used; this applies to both stereo transmissions. For stereo, pre-emphasis is applied to the left and right channels before multiplexing; the use of pre-emphasis becomes a problem because of the fact that many forms of contemporary music contain more high-frequency energy than the musical styles which prevailed at the birth of FM broadcasting. Pre-emphasizing these high frequency sounds would cause excessive deviation of the FM carrier. Modulation control devices are used to prevent this.
Systems more modern than FM broadcasting tend to use either programme-dependent variable pre-emphasis. Long before FM stereo transmission was considered, FM multiplexing of other types of audio level information was experimented with. Edwin Armstrong who invented FM was the first to experiment with multiplexing, at his experimental 41 MHz station W2XDG located on the 85th floor of the Empire State Building in New York City; these FM multiplex transmissions started in November 1934 and consisted of the main channel audio program and three subcarriers: a fax program, a synchronizing signal for the fax program and a telegraph “order” channel. These original FM multiplex subcarriers were amplitude modulated. Two musical programs, consisting of both the Red and Blue Network program feeds of the NBC Radio Network, were transmitted using the same system of subcarrier modulation as part of a studio-to-transmitter link system. In April 1935, the AM subcarriers were replaced with much improved results.
The first FM subcarrier transmissions emanating from Major Armstrong's experimental station KE2XCC at Alpine, New Jersey occurred in 1948. These transmissions consisted of two-cha