1.
Geneva
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Geneva is the second most populous city in Switzerland and is the most populous city of Romandy, the French-speaking part of Switzerland. Situated where the Rhône exits Lake Geneva, it is the capital of the Republic, the municipality has a population of 198,072, and the canton has 484,736 residents. In 2014, the compact agglomération du Grand Genève had 946,000 inhabitants in 212 communities in both Switzerland and France, within Swiss territory, the commuter area named Métropole lémanique contains a population of 1.25 million. This area is essentially spread east from Geneva towards the Riviera area and north-east towards Yverdon-les-Bains, Geneva is the city that hosts the highest number of international organizations in the world. It is also the place where the Geneva Conventions were signed, Geneva was ranked as the worlds ninth most important financial centre for competitiveness by the Global Financial Centres Index, ahead of Frankfurt, and third in Europe behind London and Zürich. A2009 survey by Mercer found that Geneva has the third-highest quality of life of any city in the world, the city has been referred to as the worlds most compact metropolis and the Peace Capital. In 2009 and 2011, Geneva was ranked as, respectively, the city was mentioned in Latin texts, by Caesar, with the spelling Genava, probably from a Celtic toponym *genawa- from the stem *genu-, in the sense of a bending river or estuary. The medieval county of Geneva in Middle Latin was known as pagus major Genevensis or Comitatus Genevensis, the name takes various forms in modern languages, Geneva /dʒᵻˈniːvə/ in English, French, Genève, German, Genf, Italian, Ginevra, and Romansh, Genevra. The city in origin shares its name, *genawa estuary, with the Italian port city of Genoa, Geneva was an Allobrogian border town, fortified against the Helvetii tribe, when the Romans took it in 121 BC. It became Christian under the Late Roman Empire, and acquired its first bishop in the 5th century, having been connected to the bishopric of Vienne in the 4th. In the Middle Ages, Geneva was ruled by a count under the Holy Roman Empire until the late 14th century, around this time the House of Savoy came to dominate the city. In the 15th century, a republican government emerged with the creation of the Grand Council. In 1541, with Protestantism in the ascendancy, John Calvin, by the 18th century, however, Geneva had come under the influence of Catholic France, which cultivated the city as its own. France also tended to be at odds with the ordinary townsfolk, in 1798, revolutionary France under the Directory annexed Geneva. At the end of the Napoleonic Wars, on 1 June 1814, in 1907, the separation of Church and State was adopted. Geneva flourished in the 19th and 20th centuries, becoming the seat of international organizations. Geneva is located at 46°12 North, 6°09 East, at the end of Lake Geneva. It is surrounded by two chains, the Alps and the Jura
2.
Switzerland
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Switzerland, officially the Swiss Confederation, is a federal republic in Europe. It consists of 26 cantons, and the city of Bern is the seat of the federal authorities. The country is situated in western-Central Europe, and is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland is a country geographically divided between the Alps, the Swiss Plateau and the Jura, spanning an area of 41,285 km2. The establishment of the Old Swiss Confederacy dates to the medieval period, resulting from a series of military successes against Austria. Swiss independence from the Holy Roman Empire was formally recognized in the Peace of Westphalia in 1648. The country has a history of armed neutrality going back to the Reformation, it has not been in a state of war internationally since 1815, nevertheless, it pursues an active foreign policy and is frequently involved in peace-building processes around the world. In addition to being the birthplace of the Red Cross, Switzerland is home to international organisations. On the European level, it is a member of the European Free Trade Association. However, it participates in the Schengen Area and the European Single Market through bilateral treaties, spanning the intersection of Germanic and Romance Europe, Switzerland comprises four main linguistic and cultural regions, German, French, Italian and Romansh. Due to its diversity, Switzerland is known by a variety of native names, Schweiz, Suisse, Svizzera. On coins and stamps, Latin is used instead of the four living languages, Switzerland is one of the most developed countries in the world, with the highest nominal wealth per adult and the eighth-highest per capita gross domestic product according to the IMF. Zürich and Geneva have each been ranked among the top cities in the world in terms of quality of life, with the former ranked second globally, according to Mercer. The English name Switzerland is a compound containing Switzer, a term for the Swiss. The English adjective Swiss is a loan from French Suisse, also in use since the 16th century. The name Switzer is from the Alemannic Schwiizer, in origin an inhabitant of Schwyz and its associated territory, the Swiss began to adopt the name for themselves after the Swabian War of 1499, used alongside the term for Confederates, Eidgenossen, used since the 14th century. The data code for Switzerland, CH, is derived from Latin Confoederatio Helvetica. The toponym Schwyz itself was first attested in 972, as Old High German Suittes, ultimately related to swedan ‘to burn’
3.
Houlin Zhao
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Houlin Zhao was elected as International Telecommunication Union Secretary-General at the 2014 ITU Plenipotentiary Conference. Mr Zhao was elected Director of ITU Telecommunication Standardization Bureau in Minneapolis, USA in 1998 and re-elected for a term in Marrakech. This led to the adoption of a Common Patent Policy for ITU/ISO/IEC still in use today, during his term of office, he also spearheaded the introduction of new efficiency measures to improve ITUs standards-making environment and strengthen its promotion. He enhanced the strategic partnership between Member States and Sector Members, while initiating and maintaining relationships with industry members. As Deputy Secretary General, he assisted the Secretary General, Dr. Hamadoun I and he also supervised membership reform with the introduction of academic institutions to ITU’s membership, implemented ‘market price’ and ‘membership priorities’. He also led an ITU delegation to participate in the United Nations Conference on Sustainable Development, held in Brazil, Mr Zhao was elected ITU Secretary-General on the 23rd October 2014. I sincerely thank all of you for your confidence in me. ”According to a interview with ITU News, Mr Zhao’s top priorities at ITU Secretary-General are, ITU membership, ITU’s effectiveness. His manifesto for the post of Secretary-General is based on three key points, vision, action and harmony. Born in 1950 in Jiangsu, China, Houlin Zhao graduated from the Nanjing University of Posts and Telecommunications, Mr Zhao is married and has one son and two grandchildren. He is fluent in three of the official UN languages – English, French and Chinese
4.
Bern
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The city of Bern or Berne is the de facto capital of Switzerland, referred to by the Swiss as their Bundesstadt, or federal city. With a population of 141,762, Bern is the fourth-most populous city in Switzerland, the Bern agglomeration, which includes 36 municipalities, had a population of 406,900 in 2014. The metropolitan area had a population of 660,000 in 2000, Bern is also the capital of the canton of Bern, the second-most populous of Switzerlands cantons. The official language in Bern is German, but the language is an Alemannic Swiss German dialect. In 1983, the old town in the centre of Bern became a UNESCO World Heritage Site. Bern is ranked among the top ten cities for the best quality of life. The etymology of the name Bern is uncertain and it has long been considered likely that the city was named after the Italian city of Verona, which at the time was known as Bern in Middle High German. As a result of the find of the Bern zinc tablet in the 1980s, it is now common to assume that the city was named after a pre-existing toponym of Celtic origin. The bear was the animal of the seal and coat of arms of Bern from at least the 1220s. The earliest reference to the keeping of bears in the Bärengraben dates to the 1440s. No archaeological evidence that indicates a settlement on the site of city centre prior to the 12th century has been found so far. In antiquity, a Celtic oppidum stood on the Engehalbinsel north of Bern, fortified since the second century BC, during the Roman era, a Gallo-Roman vicus was on the same site. The Bern zinc tablet has the name Brenodor, in the Early Middle Ages, a settlement in Bümpliz, now a city district of Bern, was some 4 km from the medieval city. The medieval city is a foundation of the Zähringer ruling family, according to 14th-century historiography, Bern was founded in 1191 by Berthold V, Duke of Zähringen. In 1218, after Berthold died without an heir, Bern was made an imperial city by the Goldene Handfeste of Holy Roman Emperor Frederick II. In 1353, Bern joined the Swiss Confederacy, becoming one of the eight cantons of the period of 1353 to 1481. The city grew out towards the west of the boundaries of the peninsula formed by the river Aare, the Zytglogge tower marked the western boundary of the city from 1191 until 1256, when the Käfigturm took over this role until 1345. It was, in turn, succeeded by the Christoffelturm until 1622, during the time of the Thirty Years War, two new fortifications – the so-called big and small Schanze – were built to protect the whole area of the peninsula
5.
Lisbon
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Lisbon is the capital and the largest city of Portugal, with a population of 552,700 within its administrative limits in an area of 100.05 km². Its urban area extends beyond the administrative limits with a population of around 2.7 million people. About 2.8 million people live in the Lisbon Metropolitan Area and it is continental Europes westernmost capital city and the only one along the Atlantic coast. Lisbon lies in the western Iberian Peninsula on the Atlantic Ocean, the westernmost areas of its metro area is the westernmost point of Continental Europe. Lisbon is recognised as a city because of its importance in finance, commerce, media, entertainment, arts, international trade, education. It is one of the economic centres on the continent, with a growing financial sector. Humberto Delgado Airport serves over 20 million passengers annually, as of 2015, and the motorway network, the city is the 7th-most-visited city in Southern Europe, after Istanbul, Rome, Barcelona, Madrid, Athens and Milan, with 1,740,000 tourists in 2009. The Lisbon region contributes with a higher GDP PPP per capita than any region in Portugal. Its GDP amounts to 96.3 billion USD and thus $32,434 per capita, the city occupies 32nd place of highest gross earnings in the world. Most of the headquarters of multinationals in the country are located in the Lisbon area and it is also the political centre of the country, as its seat of Government and residence of the Head of State. Lisbon is one of the oldest cities in the world, julius Caesar made it a municipium called Felicitas Julia, adding to the name Olissipo. Ruled by a series of Germanic tribes from the 5th century, in 1147, the Crusaders under Afonso Henriques reconquered the city and since then it has been a major political, economic and cultural centre of Portugal. Unlike most capital cities, Lisbons status as the capital of Portugal has never been granted or confirmed officially – by statute or in written form. Its position as the capital has formed through constitutional convention, making its position as de facto capital a part of the Constitution of Portugal. It has one of the warmest winters of any metropolis in Europe, the typical summer season lasts about four months, from June to September, although also in April temperatures sometimes reach around 25 °C. Although modern archaeological excavations show a Phoenician presence at this location since 1200 BC, another conjecture based on ancient hydronymy suggests that the name of the settlement derived from the pre-Roman appellation for the Tagus, Lisso or Lucio. Lisbons name was written Ulyssippo in Latin by the geographer Pomponius Mela and it was later referred to as Olisippo by Pliny the Elder and by the Greeks as Olissipo or Olissipona. The Indo-European Celts invaded in the 1st millennium BC, mixing with the Pre-Indo-European population and this indigenous settlement maintained commercial relations with the Phoenicians, which would account for the recent findings of Phoenician pottery and other material objects
6.
Antenna (radio)
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In radio and electronics, an antenna, or aerial, is an electrical device which converts electric power into radio waves, and vice versa. It is usually used with a transmitter or radio receiver. In reception, an antenna intercepts some of the power of a wave in order to produce a tiny voltage at its terminals. Antennas are essential components of all equipment that uses radio, typically an antenna consists of an arrangement of metallic conductors, electrically connected to the receiver or transmitter. These time-varying fields radiate away from the antenna into space as a transverse electromagnetic field wave. Antennas can be designed to transmit and receive radio waves in all directions equally. The first antennas were built in 1888 by German physicist Heinrich Hertz in his experiments to prove the existence of electromagnetic waves predicted by the theory of James Clerk Maxwell. Hertz placed dipole antennas at the point of parabolic reflectors for both transmitting and receiving. He published his work in Annalen der Physik und Chemie, the words antenna and aerial are used interchangeably. Occasionally the term aerial is used to mean a wire antenna, however, note the important international technical journal, the IEEE Transactions on Antennas and Propagation. In the United Kingdom and other areas where British English is used, the origin of the word antenna relative to wireless apparatus is attributed to Italian radio pioneer Guglielmo Marconi. In the summer of 1895, Marconi began testing his wireless system outdoors on his fathers estate near Bologna, Marconi discovered that by raising the aerial wire above the ground and connecting the other side of his transmitter to ground, the transmission range was increased. Soon he was able to transmit signals over a hill, a distance of approximately 2.4 kilometres, in Italian a tent pole is known as lantenna centrale, and the pole with the wire was simply called lantenna. Until then wireless radiating transmitting and receiving elements were simply as aerials or terminals. Because of his prominence, Marconis use of the word spread among wireless researchers. In common usage, the antenna may refer broadly to an entire assembly including support structure, enclosure. Especially at microwave frequencies, an antenna may include not only the actual electrical antenna. An antenna, in converting radio waves to electrical signals or vice versa, is a form of transducer, Antennas are required by any radio receiver or transmitter to couple its electrical connection to the electromagnetic field
7.
Dipole antenna
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In radio and telecommunications a dipole antenna or doublet is the simplest and most widely used class of antenna. A dipole antenna consists of two identical conductive elements such as metal wires or rods, which are usually bilaterally symmetrical. The driving current from the transmitter is applied, or for receiving antennas the output signal to the receiver is taken, between the two halves of the antenna, each side of the feedline to the transmitter or receiver is connected to one of the conductors. This contrasts with an antenna, which consists of a single rod or conductor with one side of the feedline connected to it. A common example of a dipole is the rabbit ears television antenna found on broadcast television sets and this is the simplest type of antenna from a theoretical point of view. Dipoles are resonant antennas, meaning that the serve as resonators, with standing waves of radio current flowing back. So the length of the elements is determined by the wavelength of the radio waves used. The most common form is the dipole, in which each of the two rod elements is approximately 1/4 wavelength long, so the whole antenna is a half-wavelength long. The radiation pattern of a dipole is omnidirectional, it radiates equal power in all azimuthal directions perpendicular to the axis of the antenna. For a half-wave dipole the radiation is maximum,2.15 dBi perpendicular to the axis, falling monotonically with elevation angle to zero on the axis. Several different variations of the dipole are also used, such as the dipole, short dipole, cage dipole, bow-tie. The dipole was the earliest type of antenna, it was invented by German physicist Heinrich Hertz around 1886 in his investigations of radio waves. The feedpoint impedance of an antenna is very sensitive to its electrical length. Therefore, a dipole will generally only perform optimally over a narrow bandwidth. The real and imaginary components of impedance, as a function of electrical length, are shown in the accompanying graph. The detailed calculation of these numbers are described below, note that the value of the reactance is highly dependent on the diameter of the conductors, this plot is for conductors with a diameter of.001 wavelengths. Dipoles that are smaller than the wavelength of the signal are called short dipoles. These have a low radiation resistance making them inefficient antennas
8.
Loop antenna
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A loop antenna is a radio antenna consisting of a loop or coil of wire, tubing, or other electrical conductor with its ends connected to a balanced transmission line. Small loops have low resistance and thus poor efficiency and are mainly used as receiving antennas at low frequencies. To increase the field in the loop and thus the efficiency, the coil of wire is often wound around a ferrite rod magnetic core. These antennas are used for radio direction finding. In amateur radio, loop antennas are used for low profile operating where larger antennas would be inconvenient, unsightly. Loop antennas are easy to build. Resonant loop antennas are large, governed by the intended wavelength of operation. Thus they are used at higher frequencies, especially VHF and UHF. They can be viewed as a folded dipole deformed into a different shape, although a resonant loop may be in the shape of a circle, distorting it into a somewhat different closed shape does not greatly alter its characteristics. For instance, the quad antenna popular in amateur radio consists of a resonant loop in a rectangular shape, or a large loop can be completely collapsed into a line, in which case it is termed a folded dipole. In the case of large loops, such as the quad or a folded dipole, on the other hand, a small loop antenna is used for wavelengths much bigger than the loop itself, its radiation resistance and efficiency are instead dependent on the area enclosed by the loop. For a given area, the length of the conductor is minimized if the shape is a circle. Although it has a similar appearance, the so-called halo antenna is not technically a loop since it possesses a break in the conductor opposite the feed point. Its characteristics are unlike that of either sort of loop antenna described in this article, also outside the scope of this article is the use of coupling coils for inductive transmission systems including LF and HF RFID tags and readers. The large or resonant loop antenna can be seen as a folded dipole which has been reformed into a circle, in order to be resonant the loop requires a circumference approximately equal to one wavelength. Contrary to the loop antenna, this design radiates in the direction normal to the plane of the loop. Therefore, these loops are installed with the plane of the loop in the vertical direction. Compared to a dipole or folded dipole, it then transmits less toward the sky or ground, further directionality can be obtained by using a loop whose circumference is not one but 3 or 5 wavelengths
9.
Monopole antenna
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A monopole antenna is a class of radio antenna consisting of a straight rod-shaped conductor, often mounted perpendicularly over some type of conductive surface, called a ground plane. The driving signal from the transmitter is applied, or for receiving antennas the output signal to the receiver is taken, between the end of the monopole and the ground plane. One side of the feedline is attached to the lower end of the monopole, and the other side is attached to the ground plane. This contrasts with an antenna which consists of two identical rod conductors, with the signal from the transmitter applied between the two halves of the antenna. The monopole is a resonant antenna, the rod functions as a resonator for radio waves, oscillating with standing waves of voltage. Therefore, the length of the antenna is determined by the wavelength of the waves it is used with. The most common form is the quarter-wave monopole, in which the antenna is approximately ¼ of the wavelength of the radio waves, the monopole antenna was invented in 1895 by radio pioneer Guglielmo Marconi, for this reason it is sometimes called the Marconi antenna. Common types of antenna are the whip, rubber ducky, helical, random wire, umbrella, inverted-L and T-antenna, inverted-F, mast radiator. The monopole antenna was invented in 1895 and patented 1896 by radio pioneer Guglielmo Marconi during his historic first experiments in radio communication and he began by using dipole antennas invented by Heinrich Hertz consisting of two identical horizontal wires ending in metal plates. For this reason the monopole is also called a Marconi antenna, like a dipole antenna, a monopole has an omnidirectional radiation pattern. It radiates vertically polarized radio waves, a monopole can be visualized as being formed by replacing the bottom half of a vertical dipole antenna with a conducting plane at right-angles to the remaining half. The general effect of small ground planes, as well as imperfectly conducting earth grounds, is to tilt the direction of maximum radiation up to higher elevation angles. This design is used for the mast radiator antennas employed in radio broadcasting at low frequencies, as well as low frequency antennas such as the T-antenna. At VHF and UHF frequencies the size of the ground plane needed is smaller, the most common antenna used in mobile phones is the inverted-F antenna, which is a variant of the inverted-L monopole. Bending over the antenna saves space and keeps the it within the bounds of the mobiles case, to improve the match the antenna is not fed from the end, rather some intermediate point, and the end is grounded instead. The quarter-wave whip and rubber ducky antennas used with handheld radios such as walkie-talkies and these dont use a ground plane, and the ground side of the transmitter is just connected to the ground connection on its circuit board. The hand and body of the person holding them may function as a ground plane. When used for broadcasting, the radio frequency power from the broadcasting transmitter is fed across the base insulator between the tower and a ground system
10.
Satellite dish
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A satellite dish is a dish-shaped type of parabolic antenna designed to receive electromagnetic signals from satellites, which transmit data transmissions or broadcasts, such as satellite television. The parabolic shape of a dish reflects the signal to the focal point. Mounted on brackets at the focal point is a device called a feedhorn. This feedhorn is essentially the front-end of a waveguide that gathers the signals at or near the focal point, the LNB converts the signals from electromagnetic or radio waves to electrical signals and shifts the signals from the downlinked C-band and/or Ku-band to the L-band range. Direct broadcast satellite dishes use an LNBF, which integrates the feedhorn with the LNB, the theoretical gain of a dish increases as the frequency increases. The actual gain depends on factors including surface finish, accuracy of shape. A typical value for a consumer type 60 cm satellite dish at 11.75 GHz is 37.50 dB, with lower frequencies, C-band for example, dish designers have a wider choice of materials. The large size of dish required for lower frequencies led to the dishes being constructed from metal mesh on a metal framework, at higher frequencies, mesh type designs are rarer though some designs have used a solid dish with perforations. A common misconception is that the LNBF, the device at the front of the dish, modern dishes intended for home television use are generally 43 cm to 80 cm in diameter, and are fixed in one position, for Ku-band reception from one orbital position. Prior to the existence of direct broadcast satellite services, home users would generally have a motorised C-band dish of up to 3 m in diameter for reception of channels from different satellites. Overly small dishes can still cause problems, however, including rain fade, in Europe, the frequencies used by DBS services are 10. 7–12.75 GHz on two polarisations H and V. This range is divided into a low band with 10. 7–11.7 GHz, and this results in two frequency bands, each with a bandwidth of about 1 GHz, each with two possible polarizations. In the LNB they become down converted to 950–2150 MHz, which is the range allocated for the satellite service on the coaxial cable between LNBF and receiver. Lower frequencies are allocated to cable and terrestrial TV, FM radio, in a single receiver residential installation there is a single coaxial cable running from the receiver set-top box in the building to the LNB on the dish. The DC electric power for the LNB is provided through the coaxial cable conductors that carry the signal to the receiver. In addition, control signals are transmitted from the receiver to the LNB through the cable. The receiver uses different power supply voltages to select antenna polarization, a satellite finder may aid in aiming. A dish that is mounted on a pole and driven by a motor or a servo can be controlled and rotated to face any satellite position in the sky
11.
Television antenna
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They can also be mounted in a loft or attic, where the dry conditions and increased elevation are advantageous for reception and antenna longevity. Outdoor antennas are more expensive and difficult to install, but are necessary for adequate reception in areas far from television stations. The most common types of antennas are the dipole and loop antennas, and for outdoor antennas the yagi, log periodic. To cover this range, antennas generally consist of multiple conductors of different lengths which correspond to the range the antenna is intended to receive. The length of the elements of a TV antenna are usually half the wavelength of the signal they are intended to receive, the wavelength of a signal equals the speed of light divided by the frequency. The design of a television broadcast receiving antenna is the same for the analog transmissions. Simple half-wave dipole antenna for VHF or UHF loop antennas that are made to be placed indoors are often used for television, these are often called rabbit ears or bunny aerials. The length of the ears can be adjusted by the user. These are not as efficient as a rooftop antenna since they are less directional. Dipole antennas are bi-directional, that is, they receive evenly forward and backwards and this makes them less efficient than antennas designed to maximize the signal from a narrower angle in one direction. These simple antennas are called set-top antennas because they were placed on top of the television set or receiver. The actual length of the ears is optimally about 91% of half the wavelength of the channel in free space. Quarter-wave television antennas are also used and these use a single element, and use the earth as a ground plane, therefore, no ground is required in the feed line. See also, Dipole antenna#Quarter-wave monopole Soon after television broadcasting switched from analog to digital broadcasting, RCA is one manufacturer which has commercially sold a flat antenna. Flat antennas are very lightweight, very thin, and square-shaped like a thin notebook and they connect to televisions, or to digital converter boxes, with a single coaxial cable, and may be sold with an optional signal amplifier. The amplifier must be plugged into a source, but the flat antenna does not require a power source. The flat antenna may need some moving around to achieve an optimum reception, an outdoor TV antenna generally consists of multiple conductive elements that are arranged such that it is a directional antenna. The length of the elements is one half of the signal wavelength
12.
Whip antenna
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A whip antenna is an antenna consisting of a straight flexible wire or rod. The bottom end of the whip is connected to the receiver or transmitter. The antenna is designed to be flexible so that it does not easily break, whip antennas for portable radios are often made of a series of interlocking telescoping metal tubes, so they can be retracted when not in use. Longer ones, made for mounting on vehicles and structures, are made of a fiberglass rod around a wire core. The most common type is the whip, which is approximately one-quarter of a wavelength long. Whips are the most common type of antenna, and are used in the HF, VHF and UHF radio bands. Larger versions mounted on roofs and radio masts are used as base station antennas for police, fire, ambulance, taxi, whip antennas 1/4 wavelength long or less have a single main lobe, with field strength maximum in horizontal directions, falling monotonically to zero on the axis. This is because they transmit equally well in all horizontal directions, whip antennas are normally designed as resonant antennas, the rod acts as a resonator for radio waves, with standing waves of voltage and current reflected back and forth from its ends. Therefore, the length of the rod is determined by the wavelength of the radio waves used. The most common length is approximately one-quarter of the wavelength, called a quarter-wave whip. If mounted above a ground plane, a quarter-wave whip has a gain twice that of a half wave dipole, or 5.19 dBi. However without a plane the gain is reduced and the radiation resistance increased. Whips mounted on vehicles use the skin of the vehicle as a ground plane. In hand-held devices usually no explicit ground plane is provided, therefore, the radio itself, and possibly the users hand, serves as a rudimentary ground plane. Since these are no larger than the size of the antenna itself and this type of antenna is called a ground plane antenna. To reduce the length of an antenna to make it less cumbersome. This allows the antenna to be much shorter than the normal length of a quarter-wavelength. The coil is added at the base of the whip or occasionally in the middle, in the most widely used form, the rubber ducky antenna, the loading coil is integrated with the antenna itself by making the whip out of a narrow helix of springy wire
13.
Balun
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A balun /ˈbælʌn/ is an electrical device that converts between a balanced signal and an unbalanced signal. A balun can take many forms and may include devices that also transform impedances, transformer baluns can also be used to connect lines of differing impedance. Sometimes, in the case of transformer baluns, they use magnetic coupling, common-mode chokes are also used as baluns and work by eliminating, rather than ignoring, common mode signals. The origin of the word balun is “balanced to unbalanced”, a variation of this device is the UNUN, which transfers signal from one unbalanced line to another. In classical transformers, there are two electrically separate windings of wire coils around the transformer’s core and this type is sometimes called a “voltage balun”. The ‘primary’ winding receives the signal, and the ‘secondary’ winding puts out the converted signal. The electrical signal in the coil is converted into a magnetic field in the transformer’s core. When the electrical current through the primary reverses, it causes the magnetic field to collapse. The collapsing magnetic field induces an electric field in the secondary winding. The ratio of loops in each winding and the efficiency of the magnetic coupling determines the ratio of electrical potential to electrical current. For idealized transformers, although the ratio of Voltage to Amperage will change in proportion to the square of the winding ratio. Generally a balun consists of two wires and a core, it converts the electrical energy of the primary wire into a magnetic field. Depending on how the secondary wire is done, the field is converted back to an electric field. An autotransformer balun has only one coil, or is made of two or more coils that have an electrical connection, the coil is typically wound on a ferrite rod or doughnut-shaped toroid. One can also make an autotransformer from a transformer by cross-wiring the primary and secondary windings. Baluns made with autotransformer windings are also called “Voltage baluns”, since they produce balanced output voltage, in all autotransformers, the single winding must have at least one extra electrical connection – called a tap or tap point – between the two ends of the winding. The current sent into the balun through one pair of connections acts as if it were a primary coil, electrical connections to parts of the coil different from the input connections have higher or lower voltages depending on the length of the coil that the output is tapped from. Unlike transformer-type baluns, autotransformer baluns connect all the connected to them to a single ground voltage level
14.
Block upconverter
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A block upconverter is used in the transmission of satellite signals. It converts a band of frequencies from a frequency to a higher frequency. Modern BUCs convert from the L band to Ku band, C band, older BUCs convert from a 70 MHz intermediate frequency to Ku band or C band. Most BUCs use phase-locked loop local oscillators and require an external 10 MHz frequency reference to maintain the correct transmit frequency, BUCs used in remote locations are often 2 or 4 W in the Ku band and 5 W in the C band. The 10 MHz reference frequency is sent on the same feedline as the main carrier. Many smaller BUCs also get their direct current over the feedline, BUCs are generally used in conjunction with low-noise block converters. The BUC, being a device, makes up the transmit side of the system, while the LNB is the down-converting device. An example of a system utilizing both a BUC and an LNB is a VSAT system, used for bidirectional Internet access via satellite. The block upconverter is a block shaped device assembled with the LNB in association with an OMT and this is opposed to other types of frequency upconverter which may be rack mounted indoors or not co-located with the dish. VSAT specific training that demonstrates the use of the block upconverter, BUCs, SSPAs, LNBs GaN vs GaAs VSAT Installation Manual with explanation of the block upconverter Swedish microwave LNB Terrasat Communications Ground Breaking IBUC
15.
Coaxial cable
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Coaxial cable, or coax, is a type of cable that has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield. Many coaxial cables also have an outer sheath or jacket. The term coaxial comes from the conductor and the outer shield sharing a geometric axis. Coaxial cable was invented by English engineer and mathematician Oliver Heaviside, Coaxial cable is used as a transmission line for radio frequency signals. Its applications include feedlines connecting radio transmitters and receivers with their antennas, computer network connections, digital audio and this allows coaxial cable runs to be installed next to metal objects such as gutters without the power losses that occur in other types of transmission lines. Coaxial cable also provides protection of the signal from external electromagnetic interference, the cable is protected by an outer insulating jacket. Normally, the shield is kept at ground potential and a signal carrying voltage is applied to the center conductor, the advantage of coaxial design is that electric and magnetic fields are restricted to the dielectric with little leakage outside the shield. Conversely, electric and magnetic fields outside the cable are largely kept from interfering with signals inside the cable, larger diameter cables and cables with multiple shields have less leakage. Common applications of coaxial cable include video and CATV distribution, RF and microwave transmission, the characteristic impedance of the cable is determined by the dielectric constant of the inner insulator and the radii of the inner and outer conductors. A controlled cable characteristic impedance is important because the source and load impedance should be matched to ensure maximum power transfer, other important properties of coaxial cable include attenuation as a function of frequency, voltage handling capability, and shield quality. Coaxial cable design choices affect physical size, frequency performance, attenuation, power handling capabilities, flexibility, strength, the inner conductor might be solid or stranded, stranded is more flexible. To get better performance, the inner conductor may be silver-plated. Copper-plated steel wire is used as an inner conductor for cable used in the cable TV industry. The insulator surrounding the conductor may be solid plastic, a foam plastic. The properties of control some electrical properties of the cable. A common choice is a solid polyethylene insulator, used in lower-loss cables, solid Teflon is also used as an insulator. Some coaxial lines use air and have spacers to keep the conductor from touching the shield. Many conventional coaxial cables use braided copper wire forming the shield and this allows the cable to be flexible, but it also means there are gaps in the shield layer, and the inner dimension of the shield varies slightly because the braid cannot be flat
16.
Counterpoise (ground system)
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In electronics and radio communication a counterpoise is a network of suspended wires or cables, used as a substitute for an earth connection in a radio antenna system. It is used with radio transmitters or receivers when an earth ground cannot be used because of high soil resistance or when an antenna is mounted above ground level, for example. It usually consists of a wire or network of horizontal wires, parallel to the ground, suspended above the ground under the antenna. The counterpoise functions as one plate of a capacitor, with the conductive layers of the earth acting as the other plate. Counterpoises are typically used in systems for radio transmitters where a good earth ground connection cannot be constructed. The ground must have a low resistance, because any resistance in the ground connection will dissipate power from the transmitter. Low-resistance grounds for radio transmitters are normally constructed of a network of buried in the earth. However, in areas with dry, sandy or rocky soil the ground has a high resistance, in these cases, a counterpoise is used. Another circumstance in which a counterpoise is used is when earth for a buried ground under the antenna mast is not available, the counterpoise functions as one plate of a large capacitor, with the conductive layers in the earth as the other plate. Since the radio frequency alternating currents from the transmitter can pass through a capacitor, the largest use of counterpoises is in transmitters on the low frequency and very low frequency bands, as they are very sensitive to ground resistance. Because of the wavelength of the radio waves, feasible antennas used at these frequencies are electrically short. The other, larger resistances in the circuit can consume significant portions of the transmitter’s power. However, at low frequencies the resistance of even a good ground system in high conductivity soil can consume a portion of the transmitter power. Another source of resistance is dielectric losses from the penetration of radio waves into the ground near the antenna due to the skin depth at low frequencies. Sometimes a counterpoise is combined with a ground, with the buried radial ground cables brought above ground near the base of the antenna to form a counterpoise. The area of the counterpoise around the base of the antenna is covered with copper screening. The size of the used for radio work depends on the wavelength of the transmit frequency. With a monopole antenna the counterpoise functions as a ground plane, to perform adequately, the counterpoise should extend at least half a wavelength from the antenna tower in all directions
17.
Antenna feed
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Antennas typically consist of a feed and additional reflecting or directive structures whose function is to form the radio waves from the feed into a beam or other desired radiation pattern. The rest of the consists of rods called parasitic elements. In more complex systems the feed can be more complicated. The antenna feed is usually considered to be all the components between the part of the antenna and the receivers first amplifier. For a transmitting antenna, the feed consists of everything after the last power amplifier, in a radar or satellite communications antenna the feed might consist of a feed horn, orthomode transducer, polarizer, frequency diplexer, waveguide, waveguide switches, rotary joint, etc. Particularly with an antenna, the antenna feed is a critical component that must be adjusted to work correctly with the antenna. Each type of line has a specific characteristic impedance. This must be matched to the impedance of the antenna and the transmitter and this adjustment is done with a device called an antenna tuner in the transmitter, and sometimes a matching network at the antenna. The degree of mismatch between the feedline and the antenna is measured by an instrument called an SWR meter, which measures the standing wave ratio on the line
18.
Feed line
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In a radio antenna, the feed line is the cable or other transmission line that connects the antenna with the radio transmitter or receiver. In a transmitting antenna, it feeds the radio frequency current from the transmitter to the antenna, in a receiving antenna it transfers the tiny RF voltage induced in the antenna by the radio wave to the receiver. In order to carry RF current efficiently, feed lines are made of specialized types of cable called transmission line, the most widely used types of feed line are coaxial cable, twin-lead, ladder line, and at microwave frequencies, waveguide. Particularly with an antenna, the feed line is a critical component that must be adjusted to work correctly with the antenna. Each type of line has a specific characteristic impedance. This must be matched to the impedance of the antenna and the transmitter and this adjustment is done with a device called an antenna tuner in the transmitter, and sometimes a matching network at the antenna. The degree of mismatch between the feedline and the antenna is measured by an instrument called an SWR meter, which measures the standing wave ratio on the line. It consists of two wire conductors running parallel to each other with a constant spacing, molded in polyethylene insulating material in a flat ribbon-like cable. The distance between the two wires is small relative to the wavelength of the RF signal carried on the wire, furthermore, the RF current in one wire is equal in magnitude and opposite in direction to the RF current on the other wire. Thus, if both wires radiate energy equally, the radiated energies will cancel each other out and there will be near zero radiation at any distance from the wire, twin lead is also immune to external noise or RF energies. Any unwanted external noise or unwanted RF energy induced on the wire from external energy sources will be induced in both wires at the time and equally in magnitude and direction. At the end of the line the inverted signal wire is restored to normal. Any noise will now be equal in magnitude and opposite in direction, twin lead is considered a Balanced line. Coaxial cable is probably the most widely used type of feedline and it consists of a wire center conductor and a braided or solid metallic shield conductor, usually copper or aluminum surrounding it. The center conductor is separated from the shield by a dielectric, usually plastic foam. The shield is covered with an outer plastic insulation jacket, coaxial cables advantage is that the enclosing shield conductor isolates the cable from external electromagnetic fields, so it is very immune to interference. Coaxial cable is considered an unbalanced line, waveguide is used at microwave frequencies, at which other types of feedline have excessive power losses. A waveguide is a metallic conductor or pipe
19.
Low-noise block downconverter
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A low-noise block downconverter is the receiving device mounted on satellite dishes used for satellite TV reception, which collects the radio waves from the dish. Also called a block, low-noise converter, or even low-noise downconverter. The LNB is a combination of low-noise amplifier, frequency mixer, local oscillator and it receives the microwave signal from the satellite collected by the dish, amplifies it, and downconverts the block of frequencies to a lower block of intermediate frequencies. The LNB is usually a box suspended on one or more short booms, or feed arms, in front of the dish reflector. The microwave signal from the dish is picked up by a feedhorn on the LNB and is fed to a section of waveguide. One or more pins, or probes, protrude into the waveguide at right angles to the axis and act as antennas. The lower frequency IF output signal emerges from a socket on the box to which the cable connects. The LNB gets its power from the receiver or set-top box and this phantom power travels to the LNB, opposite to the signals from the LNB. A corresponding component, called a block upconverter, is used at the earth station dish to convert the band of television channels to the microwave uplink frequency. The signal received by the LNB is extremely weak and it has to be amplified before downconversion, the low noise amplifier section of the LNB amplifies this weak signal while adding the minimum possible amount of noise to the signal. The low-noise quality of an LNB is expressed as the noise figure and this is the signal to noise ratio at the input divided by the signal to noise ratio at the output. It is typically expressed as a decibels value, the ideal LNB, effectively a perfect amplifier, would have a noise figure of 0 dB and would not add any noise to the signal. Every LNB off the line has a different noise figure because of manufacturing tolerances. Satellites use comparatively high radio frequencies to transmit their TV signals, as microwave satellite signals do not easily pass through walls, roofs, or even glass windows, it is preferable for satellite antennas to be mounted outdoors. The purpose of the LNB is to use the principle to take a block of relatively high frequencies. These lower frequencies travel through cables with much less attenuation, so there is much more signal left at the receiver end of the cable. It is also easier and cheaper to design electronic circuits to operate at these lower frequencies. The local oscillator frequency determines what block of incoming frequencies is downconverted to the expected by the receiver
20.
Passive radiator
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In a radio antenna, a passive radiator or parasitic element is a conductive element, typically a metal rod, which is not electrically connected to anything else. The waves from the different antenna elements interfere, strengthening the antennas radiation in the desired direction, the parasitic elements in a Yagi antenna are mounted parallel to the driven element, with all the elements usually in a line perpendicular to the direction of radiation of the antenna. What effect a parasitic element has on the pattern depends both on its separation from the next element, and on its length. The driven element of the antenna is usually a half-wave dipole, the parasitic elements are of two types. A reflector is slightly longer than a half-wavelength and it serves to reflect the radio waves in the opposite direction. A director is slightly shorter than a half-wavelength, it serves to increase the radiation in a given direction, a Yagi antenna may have a reflector on one side of the driven element, and one or more directors on the other side. All the elements are mounted on a metal beam or bracket along the antennas central axis. Although sometimes the elements are insulated from the supporting beam, often they are clamped or welded directly to it. This doesnt affect their functioning, because the RF voltage distribution along the element is maximum at the ends, the addition of parasitic elements gives a diminishing improvement in the antennas gain. Adding a reflector to a dipole, to make a 2-element Yagi, adding a director to this, to give a 3-element Yagi, gives a gain of about 7 dB over a dipole. As a rule of thumb, each additional parasitic element beyond this adds about 1 dB of gain, in an example of a parasitic element that is not rod-shaped, a parasitic microstrip patch antenna is sometimes mounted above another driven patch antenna. This antenna combination resonates at a lower frequency than the original element. However, the effect is to greatly increase the impedance bandwidth of the antenna. In some cases the bandwidth can be increased by a factor of 10, not all types of thin conductor multielement antennas have parasitic elements. The log periodic antenna is similar in appearance to a Yagi, but all of its elements are driven elements, connected to the transmitter or receiver
21.
Radio receiver
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In radio communications, a radio receiver is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna, the antenna intercepts radio waves and converts them to tiny alternating currents which are applied to the receiver, and the receiver extracts the desired information. The information produced by the receiver may be in the form of sound, a radio receiver may be a separate piece of electronic equipment, or an electronic circuit within another device. The most familiar form of radio receiver is a broadcast receiver, often just called a radio, the sound is produced either by a loudspeaker in the radio or an earphone which plugs into a jack on the radio. The radio requires electric power, provided either by batteries inside the radio or a cord which plugs into an electric outlet. All radios have a control to adjust the loudness of the audio. The frequency of radio stations is usually listed prominently in their advertising, in order to select a particular station to receive, the radio is adjusted to the frequency of the desired transmitter. In some radios this is done by the user turning a tuning knob until the station is heard in the radios loudspeaker. In most countries radio broadcasting is permitted using two different methods of modulation, that is, methods of adding the signal to the radio wave, AM and FM. In amplitude modulation the strength of the signal is varied by the audio signal. AM broadcasting is permitted on AM broadcast bands between 148 and 283 kHz in the low range and 526 and 1706 kHz in the medium frequency range of the radio spectrum. In frequency modulation the frequency of the signal is varied slightly by the audio signal. FM broadcasting is permitted in the FM broadcast bands between about 65 and 108 MHz in the high frequency range. The exact frequency ranges vary somewhat in different countries, radios sold in each receive the correct frequency range for that country. Most broadcast radios, called AM/FM radios, can receive both AM and FM bands, and have a switch to select which band to receive. Limited AM broadcasting is permitted in parts of the high frequency band called the shortwave band. Shortwave listening requires a receiver that can receive these bands, called a shortwave receiver, at these frequencies, radio waves transmitted into the sky can reflect from a layer in the atmosphere called the ionosphere, returning to earth at transcontinental distances. So shortwaves are used for long distance international broadcasting, often by governmental public service broadcasting organizations like the BBC, due to their lower frequency, AM radio stations can often be received at longer distances than FM stations, at hundreds of miles
22.
Antenna rotator
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An antenna rotator is a device which is used to change the orientation of a directional antenna. Most antenna rotators have two parts, the unit and the controller. The controller is placed near the equipment which the antenna is connected to. Rotators are commonly used in radio and military communications installations. Rotators are manufactured for different sizes of antennas and installations, for example, a consumer TV antenna rotator has enough power to turn a TV/FM or small Ham antenna. These units typically cost around US$70, heavy-duty Ham rotators are designed to turn extremely large, heavy, high frequency beam antennas, but cost hundreds and possibly thousands of dollars. As seen in the center of the picture, we can see an AzEl installation. It is a type that can control the azimuth and also the elevation direction of an antenna system or array. This type of configuration is used in Amateur radio satellite or EME communication for example. A popular AzEl rotator system for a small antenna array as shown in the reference picture would be the Yaesu G-5500. An open hardware AzEl rotator system is provided by the SatNOGS Groundstation project
23.
Stub (electronics)
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In microwave and radio-frequency engineering, a stub or resonant stub is a length of transmission line or waveguide that is connected at one end only. The free end of the stub is either left open-circuit or short-circuited, stubs may thus function as capacitors, inductors and resonant circuits at radio frequencies. Stubs work by means of standing waves of radio waves along their length and their reactive properties are determined by their physical length in relation to the wavelength of the radio waves. Therefore stubs are most commonly used in UHF or microwave circuits in which the wavelengths are short enough that the stub is conveniently small and they are often used to replace discrete capacitors and inductors, because at UHF and microwave frequencies lumped components perform poorly due to parasitic reactance. Stubs are commonly used in impedance matching circuits, frequency selective filters. Stubs can be constructed with any type of line, parallel conductor line, coaxial cable, stripline, waveguide. Stub circuits can be designed using a Smith chart, a tool which can determine what length line to use to obtain a desired reactance. Thus, depending on whether tan is positive or negative, an open circuit stub of length l will have a capacitive impedance at low frequency when β l < π /2. Above this frequency the impedance is inductive, at precisely β l = π /2 the stub presents a short circuit. This is qualitatively the same behaviour as a resonant circuit. For a lossless line the phase change constant is proportional to frequency, the impedance will not continue to rise monotonically with frequency after resonance as in a lumped tuned circuit. It will rise until the point where β l = π at which point it will be open circuit, after this point the impedance will again become capacitive and start to fall. It will continue to fall until at β l =3 π /2 it again presents a short circuit, at this point the filtering action of the stub has totally failed. This response of the stub continues to repeat with increasing frequency alternating between resonance and anti-resonance and it is not only a characteristic of stubs, but of all distributed element filters, that there is some frequency beyond which the filter fails and multiple unwanted passbands are produced. Similarly, a short stub is an anti-resonator at π /2, that is, it behaves as a parallel resonant circuit. Stubs can be used to match a load impedance to the transmission line characteristic impedance, the stub is positioned a distance from the load. The length of the stub is chosen so that it cancels the reactive part of the presented impedance. That is, the stub is made capacitive or inductive according to whether the line is presenting an inductive or capacitive impedance respectively
24.
Transmitter
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In electronics and telecommunications a transmitter or radio transmitter is an electronic device which generates a radio frequency alternating current. When a connected antenna is excited by this current, the antenna emits radio waves. The term transmitter is usually limited to equipment that generates radio waves for communication purposes, or radiolocation, such as radar and navigational transmitters. Generators of radio waves for heating or industrial purposes, such as ovens or diathermy equipment, are not usually called transmitters even though they often have similar circuits. The term is used more specifically to refer to a broadcast transmitter. This usage typically includes both the proper, the antenna, and often the building it is housed in. A transmitter can be a piece of electronic equipment, or an electrical circuit within another electronic device. A transmitter and a receiver combined in one unit is called a transceiver, the term transmitter is often abbreviated XMTR or TX in technical documents. The purpose of most transmitters is radio communication of information over a distance, the transmitter combines the information signal to be carried with the radio frequency signal which generates the radio waves, which is called the carrier signal. The information can be added to the carrier in several different ways, in an amplitude modulation transmitter, the information is added to the radio signal by varying its amplitude. In a frequency modulation transmitter, it is added by varying the signals frequency slightly. Many other types of modulation are used, the radio signal from the transmitter is applied to the antenna, which radiates the energy as radio waves. The antenna may be enclosed inside the case or attached to the outside of the transmitter, as in portable devices such as phones, walkie-talkies. In more powerful transmitters, the antenna may be located on top of a building or on a tower, and connected to the transmitter by a feed line. The first primitive radio transmitters were built by German physicist Heinrich Hertz in 1887 during his investigations of radio waves. These generated radio waves by a high voltage spark between two conductors, beginning in 1895 Guglielmo Marconi developed the first practical radio communication systems using spark transmitters. These spark-gap transmitters were used during the first three decades of radio, called the wireless telegraphy or spark era, vacuum tube transmitters took over because they were inexpensive and produced continuous waves, which could be modulated to transmit audio using amplitude modulation. This made possible commercial AM radio broadcasting, which began in about 1920, experimental television transmission had been conducted by radio stations since the late 1920s, but practical television broadcasting didnt begin until the 1940s
25.
Antenna tuner
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Similar matching networks are used in other equipment to transform impedance. An antennas impedance is different at different frequencies, coupling through an ATU allows the use of one antenna on a broad range of frequencies. However, despite its name, an antenna ‘tuner ’ actually matches the transmitter only to the complex impedance reflected back to the end of the feedline. If both tuner and transmission line were lossless, tuning at the end would produce a match at every point in the transmitter/feedline/antenna system. With practical systems, feed line losses limit the ability of the antenna ‘tuner’ to match the antenna or change its resonant frequency, with lossy feedlines, maximum power transfer only occurs if matching is done at both ends of the line. Transformers, autotransformers, and baluns are sometimes incorporated into the design of narrow band antenna tuners, solid-state power amplifiers operating from 1–30 MHz typically use one or more wideband transformers wound on ferrite cores. MOSFETs and bipolar transistors are designed to operate into a low impedance, so the transformer primary typically has a single turn. This feedline system design has the advantage of reducing the retuning required when the frequency is changed. A similar design can match an antenna to a line, For example, many TV antennas have a 300 Ohm impedance. A small ferrite core transformer makes the broad band impedance transformation and this transformer does not need, nor is it capable of adjustment. For receive-only use in a TV the small SWR variation with frequency is not a major problem and it should be added that many ferrite based transformers perform a balanced to unbalanced transformation along with the impedance change. When the balanced to unbalanced function is present these transformers are called a balun, the most common baluns have either a 1,1 or a 1,4 impedance transformation. There are several designs for impedance matching using an autotransformer, which is a transformer with different connection points or taps spaced along the windings. When autotransformers connect balanced and unbalanced lines they are called baluns, when two differently-grounded cables or circuits must be connected but the grounds kept independent, a full, two-winding transformer with the desired ratio is used instead. The circuit pictured at the right has three identical windings wrapped in the direction around either an air core or ferrite core. The three equal windings shown are wired for a ground shared by two unbalanced lines, and can be used as 1,1,1,4, or 1,9 impedance match. Notice that on the side, the line with more windings measures greater impedance for the same 10 Ohm load on the right. The narrow-band methods described below cover a much smaller span of frequencies
26.
Twin-lead
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Twin-lead cable is a two-conductor flat cable used as a balanced transmission line to carry radio frequency signals. It is constructed of two stranded copper or copper-clad steel wires, held a precise distance apart by a plastic ribbon. The uniform spacing of the wires is the key to the function as a transmission line. The plastic also covers and insulates the wires, however, twin-lead is more vulnerable to interference. Proximity to metal objects will inject signals into twin-lead that would be blocked out by coaxial cable, twin lead therefore requires careful installation around rain gutters, and standoffs from metal support masts. Twin-lead is also susceptible to significant degradation when wet or ice covered, for these reasons, coax has largely replaced twin-lead in most uses, except where maximum signal is required. The characteristic impedance of twin-lead is a function of the diameter and its spacing, in 300 ohm twin-lead, the most common type. This is well matched with the impedance of a folded dipole antenna. Twin-lead generally has higher impedance than the other common transmission wiring, the widely used RG-6 coax has a characteristic impedance of 75 ohms, which requires the use of a balun to match impedance when used with common antenna types. Twin lead and other types of transmission line are mainly used to connect radio transmitters and receivers to their antennas. Parallel transmission line has the advantage that its losses are an order of smaller than that of coaxial cable. Its disadvantages are that it is vulnerable to interference. For this reason, when installed along the outside of buildings and on antenna masts and it is also common practice to twist the twin lead on long free standing lengths to further reject any induced imbalances to the line. Twin-lead is supplied in different sizes, with values of 600,450,300. The most common,300 ohm twin-lead, was widely used to connect television sets. 300 ohm twin-lead for television installations has been replaced with 75 ohm coaxial cable feedlines. Twin-lead is also used in radio stations as a transmission line for balanced transmission of radio frequency signals. Twin lead is a form of balanced transmission line
27.
Antenna farm
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The history of the term antenna farm is uncertain, but it dates to at least the 1950s. In telecom circles, any area more than three antennas could be referred to as an antenna farm. In the case of an AM broadcasting station, the multiple mast radiators may all be part of a system for a single station. Alternatively, a tower with many separate antennas is often called a candelabra tower. This is not only for the security of the location. With a clearer line of sight in both cases, more signal can be received, multiple small towers also allow stations to have backup facilities co-located on each others towers for redundancy. Cleveland, Ohio has its antenna farm in the suburb of Parma, in addition, all three network affiliates and one of the 3 major radio groups have their studio facilities located within the Oklahoma City tower farm. In the Appalachian Mountains of the Eastern United States, Poor Mountain serves most of the FM, holston Mountain in upper East Tennessee is home to most of the FM and TV stations in the Tri-Cities DMA. Other examples are Signal Mountain near Chattanooga, Tennessee, Sharps Ridge in Knoxville, Tennessee, probably the most famous broadcast antenna farm of all is the World Trade Center Tower One, on which many of the New York City television and several FM stations had their antennas. All were lost when Twin Towers One and Two collapsed after the September 11 attacks in 2001, most of those stations now broadcast from their previous home,200 feet lower, on the Empire State Building. Antenna farms have often been the source of complaints from local neighborhoods and this has been increasingly so for TV stations, which have been pursuing with alacrity the construction of new digital television antennas. One such situation was in Colorado, in the late 1990s, many of the Denver metropolitan area TV stations already transmitted analog TV from Lookout Mountain, but needed the extra space for more antennas. Residents and the city of Golden filed legal objections, including challenging the authority of the Federal Communications Commission to override denial of zoning permits by local government, the city of Golden also sought to condemn the site, even though it was outside city limits. It was decided that scenic Eldorado Mountain near Boulder might be a better site, despite other alternatives, the new supertower was forced on Lookout Mountain by the U. S. Congress, allowing the existing towers to be removed in 2009 after analog shutdown. The site began operating in spring 2008
28.
Amateur radio
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The amateur radio service is established by the International Telecommunication Union through the International Telecommunication Regulations. National governments regulate technical and operational characteristics of transmissions and issue individual stations licenses with a call sign. Prospective amateur operators are tested for their understanding of key concepts in electronics, according to an estimate made in 2011 by the American Radio Relay League, two million people throughout the world are regularly involved with amateur radio. About 830,000 amateur radio stations are located in IARU Region 2 followed by IARU Region 3 with about 750,000 stations, a significantly smaller number, about 400,000, are located in IARU Region 1. The origins of amateur radio can be traced to the late 19th century, the First Annual Official Wireless Blue Book of the Wireless Association of America, produced in 1909, contains a list of amateur radio stations. This radio callbook lists wireless telegraph stations in Canada and the United States, as with radio in general, amateur radio was associated with various amateur experimenters and hobbyists. Amateur radio enthusiasts have significantly contributed to science, engineering, industry, research by amateur operators has founded new industries, built economies, empowered nations, and saved lives in times of emergency. Ham radio can also be used in the classroom to teach English, map skills, geography, math, science, the term ham radio was first a pejorative that mocked amateur radio operators with a 19th-century term for being bad at something, like ham-fisted or ham actor. It had already used for bad wired telegraph operators. Subsequently, the community adopted it as a moniker, much like the Know-Nothing Party, or other groups. Other, more entertaining explanations have grown up throughout the years, the many facets of amateur radio attract practitioners with a wide range of interests. Many amateurs begin with a fascination of radio communication and then combine other personal interests to make pursuit of the hobby rewarding, some of the focal areas amateurs pursue include radio contesting, radio propagation study, public service communication, technical experimentation, and computer networking. Amateur radio operators use various modes of transmission to communicate, the two most common modes for voice transmissions are frequency modulation and single sideband. FM offers high quality audio signals, while SSB is better at long distance communication when bandwidth is restricted. Radiotelegraphy using Morse code, also known as CW from continuous wave, is the extension of landline telegraphy developed by Samuel Morse. Morse, using internationally agreed message encodings such as the Q code, a similar legacy mode popular with home constructors is amplitude modulation, pursued by many vintage amateur radio enthusiasts and aficionados of vacuum tube technology. Demonstrating a proficiency in Morse code was for years a requirement to obtain an amateur license to transmit on frequencies below 30 MHz. Following changes in regulations in 2003, countries are no longer required to demand proficiency
29.
Cellular network
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A cellular network or mobile network is a communication network where the last link is wireless. The network is distributed over land areas called cells, each served by at least one fixed-location transceiver and this base station provides the cell with the network coverage which can be used for transmission of voice, data and others. A cell might use a different set of frequencies from neighboring cells, to avoid interference, when joined together these cells provide radio coverage over a wide geographic area. This allows mobile phones and mobile computing devices to be connected to the switched telephone network. Private cellular networks can be used for research or for large organizations and fleets, each of these cells is assigned with multiple frequencies which have corresponding radio base stations. The group of frequencies can be reused in other cells, provided that the frequencies are not reused in adjacent neighboring cells as that would cause co-channel interference. If there is a single transmitter, only one transmission can be used on any given frequency. Unfortunately, there is some level of interference from the signal from the other cells which use the same frequency. This means that, in a standard FDMA system, there must be at least a one cell gap between cells which reuse the same frequency, in the simple case of the taxi company, each radio had a manually operated channel selector knob to tune to different frequencies. As the drivers moved around, they would change from channel to channel, the drivers knew which frequency covered approximately what area. When they did not receive a signal from the transmitter, they would try other channels until they found one that worked, the taxi drivers would only speak one at a time, when invited by the base station operator. With TDMA, the transmitting and receiving time slots used by different users in each cell are different from each other, with FDMA, the transmitting and receiving frequencies used by different users in each cell are different from each other. In a simple system, the taxi driver manually tuned to a frequency of a chosen cell to obtain a strong signal. The principle of CDMA is more complex, but achieves the same result, time division multiple access is used in combination with either FDMA or CDMA in a number of systems to give multiple channels within the coverage area of a single cell. The key characteristic of a network is the ability to re-use frequencies to increase both coverage and capacity. The elements that determine frequency reuse are the distance and the reuse factor. The reuse distance, D is calculated as D = R3 N, cells may vary in radius from 1 to 30 kilometres. The boundaries of the cells can also overlap between adjacent cells and large cells can be divided into smaller cells, the frequency reuse factor is the rate at which the same frequency can be used in the network
30.
Hotspot (Wi-Fi)
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A hotspot is a physical location where people may obtain Internet access, typically using Wi-Fi technology, via a wireless local area network using a router connected to an internet service provider. Public hotspots may be found in a number of businesses for use of customers in developed urban areas throughout the world. Many hotels offer wifi access to guests, either in guest rooms or in the lobby, Hotspots differ from wireless access points, which are the hardware devices used to provide a wireless network service. Private hotspots allow Internet access to a device via another device which may have access via say a mobile device. Public access wireless local area networks were first proposed by Henrik Sjödin at the NetWorld+Interop conference in The Moscone Center in San Francisco in August 1993, Sjödin did not use the term hotspot but referred to publicly accessible wireless LANs. The first commercial venture to attempt to create a local area access network was a firm founded in Richardson. The founders of the venture, Mark Goode, Greg Jackson, the firm was one of the first to sign such public access locations as Starbucks, American Airlines, and Hilton Hotels. The company was sold to Deutsche Telecom in 2001, who converted the name of the firm into T-Mobile Hotspot. It was then that the term entered the popular vernacular as a reference to a location where a publicly accessible wireless LAN is available. ABI Research reported there was a total of 4.9 million global Wi-Fi hotspots in 2012 and projected that number would surpass 6.3 million by the end of 2013. The latest Wireless Broadband Alliance Industry Report outlines a scenario for the Wi-Fi market. Collectively, WBA operator members serve more than 1 billion subscribers, the public can use a laptop or other suitable portable device to access the wireless connection provided. Of the estimated 150 million laptops,14 million PDAs, and other emerging Wi-Fi devices sold per year for the last few years, most include the Wi-Fi feature. For venues that have broadband Internet access, offering wireless access is as simple as configuring one access point, in conjunction with a router, a single wireless router combining these functions may suffice. More than 10,900 hotspots are on trains, planes and airports, the region with the largest number of public hotspots is Europe, followed by North America and Asia. Security is a concern in connection with Hotspots. There are three possible attack vectors, first, there is the wireless connection between the client and the access point. This needs to be encrypted, so that the connection cannot be eavesdropped or attacked by a man-in-the-middle-attack, second, there is the Hotspot itself
31.
Municipal wireless network
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Municipal wireless network is a city-wide wireless network. This is usually done by providing municipal broadband via Wi-Fi to large parts or all of an area by deploying a wireless mesh network. The typical deployment design uses hundreds of access points deployed outdoors. The operator of the acts as a wireless internet service provider. Municipal wireless networks go far beyond the existing piggybacking opportunities available near public libraries, such networks are capable of enhancing city management and public safety, especially when used directly by city employees in the field. They can also be a service to those who cannot afford private high-speed services. When the network service is free and a number of clients consume a majority of the available capacity. In 2003, Verge Wireless formed an agreement with Tropos Networks to build a municipal wireless networks in the area of Baton Rouge. Verge Wireless built networks for Baton Rouge, New Orleans, some applications include wireless security cameras, police mug shot software, and location-based advertising. In 2006 the US Federal Trade Commission expressed concerns about such private-public partnerships as trending towards a franchise monopoly. 11b/g, a few high-end laptops at that time featured built-in support for these newer protocols. WiMAX is designed to implement a metropolitan area network while 802.11 is designed to implement a local area network. Within the United States, providing a wireless network is not recognized as a priority. Some have argued that the benefits of public approach may exceed the costs, the construction of such networks is a significant part of their lifetime costs. Usually, a private firm works with government to construct a network. Financing is usually shared by both the firm and the municipal government. Once operational, the service may be free to users via public finance or advertising, among deployed networks, usage as measured by number of distinct users has been shown to be moderate to light. Private firms serving multiple cities sometimes maintain an account for each user, as of 2007 some Muni WiFi deployments are delayed as the private and public partners negotiate the business model and financing. In such networks, radio communication is used both for the Wi-Fi service and for the backhaul or pathway to the Internet and this means that the nodes only need a wire for power
32.
Radio
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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, Radio systems need a transmitter to modulate some property of the energy produced to impress a signal on it, for example using amplitude modulation or angle modulation. Radio systems also need an antenna to convert electric currents into radio waves, an antenna can be used for both transmitting and receiving. The electrical resonance of tuned circuits in radios allow individual stations to be selected, the electromagnetic wave is intercepted by a tuned receiving antenna. Radio frequencies occupy the range from a 3 kHz to 300 GHz, a radio communication system sends signals by radio. The term radio is derived from the Latin word radius, meaning spoke of a wheel, beam of light, however, this invention would not be widely adopted. The switch to radio in place of wireless took place slowly and unevenly in the English-speaking world, the United States Navy would also play a role. Although its translation of the 1906 Berlin Convention used the terms wireless telegraph and wireless telegram, the term started to become preferred by the general public in the 1920s with the introduction of broadcasting. Radio systems used for communication have the following elements, with more than 100 years of development, each process is implemented by a wide range of methods, specialised for different communications purposes. Each system contains a transmitter, This consists of a source of electrical energy, the transmitter contains a system to modulate 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 such as amplitude, frequency, phase. Amplitude modulation of a carrier wave works by varying the strength of the signal in proportion to the information being sent. For example, changes in the strength can be used to reflect the sounds to be reproduced by a speaker. It was the used for the first audio radio transmissions. 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. FM has the capture effect whereby a receiver only receives the strongest signal, Digital data can be sent by shifting the carriers frequency among a set of discrete values, a technique known as frequency-shift keying. FM is commonly used at Very high frequency radio frequencies for high-fidelity broadcasts of music, analog TV sound is also broadcast using FM. Angle modulation alters the phase of the carrier wave to transmit a signal
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Radio masts and towers
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Radio masts and towers are, typically, tall structures designed to support antennas for telecommunications and broadcasting, including television. There are two types, guyed and self supporting structures. They are among the tallest man-made structures, masts are often named after the broadcasting organizations that originally built them or currently use them. In the case of a mast radiator or radiating tower, the whole mast or tower is itself the transmitting antenna, the terms mast and tower are often used interchangeably. However, in engineering terms, a tower is a self-supporting or cantilevered structure. Broadcast engineers in the UK use the same terminology, in US broadcast engineering, a tower is an antenna structure attached to the ground, whereas a mast is a vertical antenna support mounted on some other structure. Masts tend to be cheaper to build but require an extended area surrounding them to accommodate the guy wires, Towers are more commonly used in cities where land is in short supply. There are a few designs that are partly free-standing and partly guyed, called additionally guyed towers. For example, The Gerbrandy tower consists of a tower with a guyed mast on top. The few remaining Blaw-Knox towers do the opposite, they have a lower section surmounted by a freestanding part. Until August 8,1991, the Warsaw radio mast was the worlds tallest supported structure on land, there are over 50 radio structures in the United States that are 600 m or taller. The steel lattice is the most widespread form of construction and it provides great strength, low weight and wind resistance, and economy in the use of materials. Lattices of triangular cross-section are most common, and square lattices are also widely used, guyed masts are often used, the supporting guy lines carry lateral forces such as wind loads, allowing the mast to be very narrow and simply constructed. When built as a tower, the structure may be parallel-sided or taper over part or all of its height, when constructed of several sections which taper exponentially with height, in the manner of the Eiffel Tower, the tower is said to be an Eiffelized one. The Crystal Palace tower in London is an example, guyed masts are sometimes also constructed out of steel tubes. This construction type has the advantage that cables and other components can be protected from weather inside the tube and these masts are mainly used for FM-/TV-broadcasting, but sometimes also as mast radiator. The big mast of Mühlacker transmitting station is an example of this. A disadvantage of this mast type is that it is more affected by winds than masts with open bodies
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Wi-Fi
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Wi-Fi or WiFi is a technology for wireless local area networking with devices based on the IEEE802.11 standards. Wi-Fi is a trademark of the Wi-Fi Alliance, which restricts the use of the term Wi-Fi Certified to products that successfully complete interoperability certification testing. Devices that can use Wi-Fi technology include personal computers, video-game consoles, smartphones, digital cameras, tablet computers, digital audio players, Wi-Fi compatible devices can connect to the Internet via a WLAN network and a wireless access point. Such an access point has a range of about 20 meters indoors, hotspot coverage can be as small as a single room with walls that block radio waves, or as large as many square kilometres achieved by using multiple overlapping access points. Wi-Fi most commonly uses the 2.4 gigahertz UHF and 5 gigahertz SHF ISM radio bands, having no physical connections, it is more vulnerable to attack than wired connections, such as Ethernet. In 1971, ALOHAnet connected the Hawaiian Islands with a UHF wireless packet network, ALOHAnet and the ALOHA protocol were early forerunners to Ethernet, and later the IEEE802.11 protocols, respectively. A1985 ruling by the U. S. Federal Communications Commission released the ISM band for unlicensed use and these frequency bands are the same ones used by equipment such as microwave ovens and are subject to interference. In 1991, NCR Corporation with AT&T Corporation invented the precursor to 802.11, the first wireless products were under the name WaveLAN. They are the credited with inventing Wi-Fi. In 1992 and 1996, CSIRO obtained patents for a method used in Wi-Fi to unsmear the signal. The first version of the 802.11 protocol was released in 1997 and this was updated in 1999 with 802. 11b to permit 11 Mbit/s link speeds, and this proved to be popular. In 1999, the Wi-Fi Alliance formed as an association to hold the Wi-Fi trademark under which most products are sold. Wi-Fi uses a number of patents held by many different organizations. In April 2009,14 technology companies agreed to pay CSIRO $1 billion for infringements on CSIRO patents and this led to Australia labeling Wi-Fi as an Australian invention, though this has been the subject of some controversy. In 2016, the local area network Test Bed was chosen as Australias contribution to the exhibition A History of the World in 100 Objects held in the National Museum of Australia. The name Wi-Fi, commercially used at least as early as August 1999, was coined by the brand-consulting firm Interbrand, the Wi-Fi Alliance had hired Interbrand to create a name that was a little catchier than IEEE802. 11b Direct Sequence. Phil Belanger, a member of the Wi-Fi Alliance who presided over the selection of the name Wi-Fi, has stated that Interbrand invented Wi-Fi as a pun upon the word hi-fi. Interbrand also created the Wi-Fi logo, the yin-yang Wi-Fi logo indicates the certification of a product for interoperability
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Wireless
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Wireless communication, or sometimes simply wireless, is the transfer of information or power between two or more points that are not connected by an electrical conductor. The most common wireless technologies use radio waves, with radio waves distances can be short, such as a few meters for television or as far as thousands or even millions of kilometers for deep-space radio communications. It encompasses various types of fixed, mobile, and portable applications, including radios, cellular telephones, personal digital assistants. Somewhat less common methods of achieving wireless communications include the use of other wireless technologies, such as light, magnetic. The term wireless has been used twice in history, with slightly different meaning. It was initially used from about 1890 for the first radio transmitting and receiving technology, as in wireless telegraphy and this became its primary usage in the 2000s, due to the advent of technologies such as LTE, LTE-Advanced, Wi-Fi and Bluetooth. Wireless operations permit services, such as communications, that are impossible or impractical to implement with the use of wires. The term is used in the telecommunications industry to refer to telecommunications systems which use some form of energy to transfer information without the use of wires. Information is transferred in this manner over both short and long distances, similar to free-space optical communication, the photophone also required a clear line of sight between its transmitter and its receiver. It would be decades before the photophones principles found their first practical applications in military communications. Marconi soon developed a system that was transmitting signals way beyond distances anyone could have predicted, guglielmo Marconi and Karl Ferdinand Braun were awarded the 1909 Nobel Prize for Physics for their contribution to this form of wireless telegraphy. Free space means the light travel through the open air or outer space. This contrasts with other technologies that use light beams traveling through transmission lines such as optical fiber or dielectric light pipes. The technology is useful where physical connections are due to high costs or other considerations. Sonic, especially ultrasonic short range communication involves the transmission and reception of sound, electromagnetic induction has short range communication and power. This has been used in situations such as pacemakers, as well as for short-range Rfid tags. Common examples of wireless equipment include, Infrared and ultrasonic remote control devices Professional LMR and SMR typically used by business, industrial, consumer Two-way radio including FRS Family Radio Service, GMRS and Citizens band radios. Consumer and professional Marine VHF radios, airband and radio navigation equipment used by aviators and air traffic control Cellular telephones and pagers, provide connectivity for portable and mobile applications, both personal and business
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Mobile phone radiation and health
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The effect of mobile phone radiation on human health is a subject of interest and study worldwide, as a result of the enormous increase in mobile phone usage throughout the world. As of 2015, there were 7.4 billion subscriptions worldwide, mobile phones use electromagnetic radiation in the microwave range. Other digital wireless systems, such as data communication networks, produce similar radiation, mobile phone use does not increase the risk of getting brain cancer or other head tumors. Evidence does not support the hypothesis that mobile phone radiation has an effect on the permeability of the blood-brain barrier, mobile phone use does not increase the risk of getting brain cancer or other head tumors. As the United States National Cancer Institute explains, Radiofrequency energy, unlike ionizing radiation and its only consistently observed biological effect in humans is tissue heating. In animal studies, it has not been found to cause cancer or to enhance the effects of known chemical carcinogens. Some users of mobile phones and similar devices have reported feeling various non-specific symptoms during, studies have failed to link any of these symptoms to electromagnetic exposure. Experts consulted by France considered it was mandatory that the antenna axis should not to be directly in front of a living place at a distance shorter than 100 metres. For radio stations, ICNIRP proposes two safety levels, one for exposure, another one for the general population. Currently there are underway to harmonise the different standards in existence. Radio base licensing procedures have been established in the majority of urban spaces regulated either at municipal/county, many governmental bodies also require that competing telecommunication companies try to achieve sharing of towers so as to decrease environmental and cosmetic impact. This issue is a factor of rejection of installation of new antennas. The safety standards in the US are set by the Federal Communications Commission, switzerland has set safety limits lower than the ICNIRP limits for certain sensitive areas. In the US, a number of personal injury lawsuits have been filed by individuals against cellphone manufacturers on the basis of allegations of causation of brain cancer. In US federal courts, expert testimony relating to science must be first evaluated by a judge, in a Daubert hearing, to be relevant and valid before it is admissible as evidence. In a 2002 case against Motorola, the plaintiffs alleged that the use of wireless handheld telephones could cause brain cancer, in February 2009, the telecom company Bouygues Telecom was ordered to take down a mobile phone mast due to uncertainty about its effect on health. Residents in the commune Charbonnières in the Rhône department had sued the company claiming adverse health effects from the emitted by the 19 meter tall antenna. As it takes time to cancer, the court disregarded short-term studies
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Focal cloud
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A focal cloud is the collection of focal points of an imperfect lens or parabolic reflector whether optical, electrostatic or electromagnetic. This includes parabolic antennas and lens-type reflective antennas of all kinds, the effect is analogous to the circle of confusion in photography. In a perfect lens or parabolic reflector, rays parallel to the devices axis striking the lens or reflector all pass through a single point, the focal point. In an imperfectly constructed lens or reflector, rays passing through different parts of the element do not converge to a point but have different focal points. The set of these focal points forms a region called the focal cloud, the diameter of the focal cloud determines the maximum resolution of the optical system. Lens-reflector artifacts, geometry and other imperfections determine the diameter of the focal cloud. A focal cloud can render a satellite dish rather inefficient in relation to its size in specific frequencies, for countering the effect, there are several techniques, either in construction of the reflectors or lenses, or in the way signal beams are concentrated. In satellite antennas, scalar rings are used to push the spread signal into the feed horn
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Ground plane
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In electrical engineering, a ground plane is an electrically conductive surface, usually connected to electrical ground. The term has two different meanings in separate areas of electrical engineering, in telecommunication, a ground plane is a flat or nearly flat horizontal conducting surface that serves as part of an antenna, to reflect the radio waves from the other antenna elements. The plane does not necessarily have to be connected to ground, Ground plane shape and size play major roles in determining its radiation characteristics including gain. To function as a plane, the conducting surface must be at least a quarter of the wavelength of the radio waves in size. In lower frequency antennas, such as the mast radiators used for broadcast antennas, for higher frequency antennas, in the VHF or UHF range, the ground plane can be smaller, and metal disks, screens and wires are used as ground planes. At upper VHF and UHF, the skin of a car or aircraft can serve as a ground plane for whip antennas projecting from it. In microstrip antennas and printed monopole antennas an area of copper foil on the side of a printed circuit board serves as a ground plane. The ground plane doesnt have to be a continuous surface, in the ground plane antenna style whip antenna, the plane consists of several wires λ/4 long radiating from the base of a quarter-wave whip antenna. The radio waves from an element that reflect off a ground plane appear to come from a mirror image of the antenna located on the other side of the ground plane. In a monopole antenna, the pattern of the monopole plus the virtual image antenna make it appear as a two element center-fed dipole antenna. So a monopole mounted over a ground plane has a radiation pattern identical to a dipole antenna. The feedline from the transmitter or receiver is connected between the end of the monopole element and the ground plane. The ground plane must have good conductivity, any resistance in the plane is in series with the antenna. A ground plane on a circuit board is a large area or layer of copper foil connected to the circuits ground point. It serves as the path for current from many different components. A ground plane is made as large as possible, covering most of the area of the PCB which is not occupied by circuit traces. In multilayer PCBs, it is often a separate layer covering the entire board, when digital circuits switch state, large current pulses flow from the active devices through the ground circuit. If the power supply and ground traces have significant impedance, the drop across them may create noise voltage pulses that disturb other parts of the circuit
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Main lobe
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In a radio antennas radiation pattern, the main lobe, or main beam is the lobe containing the maximum power. This is the lobe that exhibits the greatest field strength, the other lobes are called sidelobes, and usually represent unwanted radiation in undesired directions. The sidelobe in the direction from the main lobe is called the backlobe. Side lobe Beamwidth Software defined antenna This article incorporates public domain material from the General Services Administration document Federal Standard 1037C
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Near and far field
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The near field and far field are regions of the electromagnetic field around an object, such as a transmitting antenna, or the result of radiation scattering off an object. Non-radiative near-field behaviors of electromagnetic fields dominate close to the antenna or scattering object, far-field E and B field strength decreases inversely with distance from the source, resulting in an inverse-square law for the radiated power intensity of electromagnetic radiation. By contrast, near-field E and B strength decrease more rapidly with distance, the far field is the region in which the field acts as normal electromagnetic radiation. In this region, it is dominated by electric or magnetic fields with electric dipole characteristics, the near field is governed by multipole type fields, which can be considered as collections of dipoles with a fixed phase relationship. The boundary between the two regions is only vaguely defined, and it depends on the dominant wavelength emitted by the source, in the far-field region of an antenna, radiation decreases as the square of distance, and absorption of the radiation does not feed back to the transmitter. However, in the region, absorption of radiation does affect the load on the transmitter. Magnetic induction can be seen as a simple model of this type of near-field electromagnetic interaction. In the far-field region, each part of the EM field is produced by a change in the part. However, in the region, the electric and magnetic fields can exist independently of each other. In a normally-operating antenna, positive and negative charges have no way of leaving and are separated from each other by the excitation signal and this generates an oscillating electrical dipole, which affects both the near field and the far field. In general, the purpose of antennas is to communicate wirelessly for long distances using far fields, Also known as the radiation-zone field, the far field carries a relatively uniform wave pattern. The radiation zone is important because far fields in general fall off in amplitude by 1∕r and this means that the total energy per unit area at a distance r is proportional to 1∕r2. The area of the sphere is proportional to r2, so the energy passing through the sphere is constant. This means that the energy actually escapes to infinite distance. In contrast, the near field refers to such as near conductors. One easy to observe example is the change of noise levels picked up by a set of rabbit ear antennas when one places a body part in close range. The near-field has been of increasing interest, particularly in the development of capacitive sensing technologies such as used in smart phones. The interaction with the medium can cause energy to deflect back to the source, another intermediate region, called the transition zone, is defined on a somewhat different basis, namely antenna geometry and excitation wavelength
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Side lobe
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In antenna engineering, side lobes or sidelobes are the lobes of the far field radiation pattern that are not the main lobe. In a directional antenna in which the objective is to emit the radio waves in one direction, the lobe in that direction has a field strength than the others. The other lobes are called lobes, and usually represent unwanted radiation in undesired directions. The side lobe in the direction from the main lobe is called the back lobe. In transmitting antennas, excessive side lobe radiation wastes energy and may cause interference to other equipment, classified information may be picked up by unintended receivers. In receiving antennas, side lobes may pick up interfering signals, the power density in the side lobes is generally much less than that in the main beam. It is generally desirable to minimize the level, which is measured in decibels relative to the peak of the main beam. The main lobe and side lobes occur for both conditions of transmit, and for receive. For a rectangular aperture antenna having a uniform distribution, the first sidelobe is -13.26 dB relative to the peak of the main beam.57 dB relative to the peak of the main beam. In this case, the pattern has a canonical form of Radiation Pattern ∝10 log 10 where J1 is the Bessel function of the first kind of order 1. Side lobe levels can be reduced by tapering the edges of the distribution at the expense of reduced directivity. The nulls between sidelobes occur when the radiation passes through the origin in the complex plane. Hence, adjacent sidelobes are generally 180° out of phase to each other, larger antennas have narrower main beams, as well as narrower sidelobes. Hence, larger antennas have more sidelobes in the visible space, grating lobes are a special case of a sidelobe. In such a case, the sidelobes should be considered all the lobes lying between the main lobe and the first grating lobe, or between grating lobes. It is conceptually useful to distinguish between sidelobes and grating lobes because grating lobes have larger amplitudes than most, if not all, the mathematics of grating lobes is the same as of X-ray diffraction. Sidelobes and Beamwidths - An Antenna Tutorial
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