1.
Telecommunication
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Telecommunication is the transmission of signs, signals, messages, writings, images and sounds or intelligence of any nature by wire, radio, optical or other electromagnetic systems. Telecommunication occurs when the exchange of information between communication participants includes the use of technology and it is transmitted either electrically over physical media, such as cables, or via electromagnetic radiation. Such transmission paths are divided into communication channels which afford the advantages of multiplexing. The term is used in its plural form, telecommunications. Early means of communicating over a distance included visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, other examples of pre-modern long-distance communication included audio messages such as coded drumbeats, lung-blown horns, and loud whistles. Zworykin, John Logie Baird and Philo Farnsworth, the word telecommunication is a compound of the Greek prefix tele, meaning distant, far off, or afar, and the Latin communicare, meaning to share. Its modern use is adapted from the French, because its use was recorded in 1904 by the French engineer. Communication was first used as an English word in the late 14th century, in the Middle Ages, chains of beacons were commonly used on hilltops as a means of relaying a signal. Beacon chains suffered the drawback that they could pass a single bit of information. One notable instance of their use was during the Spanish Armada, in 1792, Claude Chappe, a French engineer, built the first fixed visual telegraphy system between Lille and Paris. However semaphore suffered from the need for skilled operators and expensive towers at intervals of ten to thirty kilometres, as a result of competition from the electrical telegraph, the last commercial line was abandoned in 1880. Homing pigeons have occasionally used throughout history by different cultures. Pigeon post is thought to have Persians roots and was used by the Romans to aid their military, frontinus said that Julius Caesar used pigeons as messengers in his conquest of Gaul. The Greeks also conveyed the names of the victors at the Olympic Games to various cities using homing pigeons, in the early 19th century, the Dutch government used the system in Java and Sumatra. And in 1849, Paul Julius Reuter started a service to fly stock prices between Aachen and Brussels, a service that operated for a year until the gap in the telegraph link was closed. Sir Charles Wheatstone and Sir William Fothergill Cooke invented the telegraph in 1837. Also, the first commercial electrical telegraph is purported to have constructed by Wheatstone and Cooke. Both inventors viewed their device as an improvement to the electromagnetic telegraph not as a new device, samuel Morse independently developed a version of the electrical telegraph that he unsuccessfully demonstrated on 2 September 1837
2.
Antenna array
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An antenna array is a set of multiple connected antennas which work together as a single antenna, to transmit or receive radio waves. The individual antenna elements are connected to a receiver or transmitter by feedlines that feed the power to the elements in a specific phase relationship. An antenna array can achieve higher gain, that is a beam of radio waves. In general, the larger the number of antenna elements used, the higher the gain. Some antenna arrays are composed of thousands of individual antennas, the term antenna array most commonly means a driven array consisting of multiple identical driven elements all connected to the receiver or transmitter, often half-wave dipoles fed in phase. A parasitic array consists of a driven element connected to the feedline. It is usually another name for a Yagi-Uda antenna, the beam of radio waves can be steered electronically to point instantly in any direction over a wide angle. However the term phased array is used to mean an ordinary array antenna. To create a high gain antenna, which radio waves in a narrow beam. A second technique is to use multiple antennas which are fed from the transmitter or receiver. In directions in which the waves from the individual antennas arrive in phase, in directions in which the individual waves arrive out of phase, with the peak of one wave coinciding with the valley of another, the waves cancel reducing the power radiated in that direction. Arrays in which the elements are fed in phase are broadside arrays. Using the technique called aperture synthesis such an array can have the resolution of an antenna with a equal to the distance between the antennas. In the technique called Very Long Baseline Interferometry dishes on separate continents have been linked, Array antennas can be divided into two classes based on how the component antennas axis is related to the direction of radiation. A broadside array is a one or two dimensional array in which the direction of radiation is perpendicular to the plane of the antennas, an endfire array is a linear array in which the direction of radiation is along the line of antennas. Driven arrays - These are arrays in which the component antennas are all driven - connected to the transmitter or receiver. Collinear array - a broadside array consisting of multiple identical dipole antennas oriented vertically in a line and this is a high gain omnidirectional antenna, often used in the VHF band as base station antennas for land mobile services. Superturnstile or Batwing array - specialized vertical antenna used for television broadcasting consisting of multiple crossed-dipole antennas mounted collinearly on a mast, high gain omnidirectional radiation pattern with wide bandwidth
3.
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
4.
Polarization (waves)
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Polarization is a parameter applying to transverse waves that specifies the geometrical orientation of the oscillations. In a transverse wave the direction of the oscillation is transverse to the direction of motion of the wave, a simple example of a polarized transverse wave is vibrations traveling along a taut string for example in a musical instrument like a guitar string. Depending on how the string is plucked, the vibrations can be in a direction, horizontal direction. Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, in some types of transverse waves the wave displacement is limited to a single direction, so these also dont exhibit polarization. For example, in waves in liquids the wave displacement of the particles is always in a vertical plane. In linear polarization the fields oscillate in a single direction, in circular or elliptical polarization the fields rotate at a constant rate in a plane as the wave travels. Polarized light can be produced by passing unpolarized light through a polarizing filter, some of these are used to make polarizing filters. Light is also partially polarized when it reflects from a surface, according to quantum mechanics, electromagnetic waves consist of particles called photons. When viewed in this way, the polarization of a wave is determined by a quantum mechanical property of photons called their spin. A photon has one of two spins, it can either spin in a right hand sense or a left hand sense about its direction of travel. Circularly polarized electromagnetic waves are composed of photons with one type of spin. Linearly polarized waves consist of numbers of right and left hand spinning photons. Polarization is an important parameter in areas of science dealing with transverse waves, such as optics, seismology, radio, especially impacted are technologies such as lasers, wireless and optical fiber telecommunications, and radar. And incoherent states can be modeled stochastically as a combination of such uncorrelated waves with some distribution of frequencies, phases. Considering a monochromatic wave of optical frequency f, let us take the direction of propagation as the z axis. Being a transverse wave the E and H fields must then contain components only in the x and y directions whereas Ez=Hz=0. Using complex notation, we understand the instantaneous electric and magnetic fields to be given by the real parts of the complex quantities occurring in the following equations. Here ex, ey, hx, and hy are complex numbers, in the second more compact form, as these equations are customarily expressed, these factors are described using the wavenumber k =2 π n / λ and angular frequency ω =2 π f
5.
Two-way radio
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A two-way radio is a radio that can do both transmit and receive a signal, unlike a broadcast receiver which only receives content. A two-way radio allows the operator to have a conversation with other similar radios operating on the radio frequency. Two-way radios are available in mobile, stationary base and hand-held portable configurations, hand-held radios are often called walkie-talkies, handie-talkies, or just hand-helds. Two-way radio systems operate in a half-duplex mode, that is, the operator can talk, or he can listen. A push-to-talk or Press To Transmit button activates the transmitter, when it is released the receiver is active, a mobile phone or cellular telephone is an example of a two-way radio that can transmit and receive at the same time, i. e. in full-duplex mode. Full-duplex is generally achieved by the use of two different frequencies or by frequency-sharing methods to carry the two directions of the conversation simultaneously, methods for mitigating the self interference caused by simultaneous same-frequency transmission and reception include using two antennas, or dynamic solid-state filters. Installation of receivers and transmitters at the fixed location allowed exchange of messages wirelessly. As early as 1907, two-way telegraphy traffic across the Atlantic Ocean was commercially available, by 1912 commercial and military ships carried both transmitters and receivers, allowing two-way communication in close to real-time with a ship that was out of sight of land. The first truly mobile two-way radio was developed in Australia in 1923 by Senior Constable Frederick William Downie of the Victorian Police. The Victoria Police were the first in the world to use communication in cars. The first sets took up the back seat of the Lancia patrol cars. As radio equipment became more powerful, compact, and easier to use, during World War II walkie-talkie hand-held radio transceivers were extensively used by air and ground troops, both by the Allies and the Axis. Early two-way schemes allowed only one station to transmit at a time while others listened, the first radio systems could not transmit voice. This required training of operators in use of Morse code, on a ship, the radio operating officers typically had no other duties than handling radio messages. When voice transmission possible, dedicated operators were no longer required. Two-way radio systems can be classified in several ways depending on their attributes, conventional radios operate on fixed RF channels. In the case of radios with multiple channels, they operate on one channel at a time, the proper channel is selected by a user. The user operates a channel selector on the control panel to pick the appropriate channel
6.
Folded unipole antenna
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The folded unipole antenna was first devised for broadcast use by John H. Mullaney, an American radio broadcast pioneer, and consulting engineer. A variation of an antenna, it consists of a vertical metal rod or mast mounted over a conductive surface called a ground plane. The mast is surrounded by a skirt of vertical wires electrically attached to the top of the mast, the wires are connected by a metal ring at the bottom and the feed line is connected between the bottom of the wires and ground. A typical AM broadcast antenna is a monopole antenna above a ground system. The ground system normally comprises 120 buried copper or phosphor bronze radial wires at least one-quarter wavelength long, all the ground system components are bonded together, usually by brazing or using coin silver solder to minimize corrosion. If required, insulated guy wires are used, radio frequency power is fed across the base insulator between the ground system and the tower itself. P = I2 R Electrically short monopole antennas have low resistance, longer antennas may have impedances that are more advantageous unless the electrical height exceeds about 5/8 of a wavelength. In any case, a network at the base of the tower matches the antenna to its transmission line. If the tower is short, it will have its capacitive reactance tuned out by this matching network. This network and tower combination often results in a narrow bandwidth, Electrically short antenna systems have relatively small apertures and high losses. Some claims have made that ground system losses are reduced for the folded unipole antenna. However the experimental work of Ronald Rackley, et al. have shown this to be incorrect, such claims do not consider that for the same conditions, the total displacement current in the ground system is nearly the same for a folded unipole as for a conventional series-fed unipole. Therefore ground system losses for these two configurations are very similar. Using a folded unipole will increase the bandwidth of electrically short antennas because its feed-point comprises less reactance that needs to be tuned out, one usually constructs the folded-unipole from an existing monopole antenna by shorting out the base insulator, thus connecting the tower directly to the ground system. The resulting skirt connects to the top and remains insulated throughout its entire length. The wires of the skirt connect at the feed-point near the bottom, below is another folded unipole antenna constructed from an existing series fed monopole. This antenna has three folds comprising the skirt. A possible improvement over the basic folded-unipole antenna is the “self resonant” unipole antenna and this reactance cancels the reactive component of the antenna input impedance causing the input impedance to appear resistive at the feed point
7.
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
8.
Mast radiator
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A mast radiator is a radio mast or tower in which the entire structure functions as an antenna. This design, developed around 1930, is used for transmitting antennas operating at low frequencies, in the VLF, LF and MF ranges. The metal mast is connected to the transmitter. Its base is mounted on a nonconductive support to insulate it from the ground. A mast radiator is a form of monopole antenna, most mast radiators are built as guyed masts insulated from the ground at the base. Steel lattice masts of triangular cross-section are the most common type, square lattice masts and tubular masts are also sometimes used. To ensure that the tower is a conductor, the towers structural sections are electrically bonded at the joints by short copper jumpers which are soldered to each side. The actual transmitter is located in a separate building, which supplies RF power to the helix building via a transmission line. Free-standing towers are used as radiating structures. These towers can have a triangular or a cross section. One of the best-known radiating towers is the Blosenbergturm in Beromünster, fiberglass masts are sometimes used for small constructions. The ideal height of a mast radiator depends on frequency, demographics for the location. When this is not possible, masts with a loading coil, the height of the mast determines the radiation properties. A focus of radiated power towards the ground is much desired on frequencies below 3 megahertz, masts longer than five eighths of the wavelength are normally not used, because they show bad vertical radiation patterns, so masts for mediumwave transmitters do not normally exceed 300 metres. For longwave transmitters, however, the construction of masts with heights of half-wave wavelength is not economically viable. The only longwave radio mast with a height of the length of the radiated wavelength was the Warszawa Radio Mast at Konstantynów. At the time of its collapse in 1991 it was the tallest manmade structure in the world, at 646.38 metres tall, for a wavelength of 1292.76 metres. For frequencies below longwave, masts are electrically enlarged by loading coils or capacity hats on the top, sectional, the structure is divided into usually two sections with insulators between, usually center-fed
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.
Turnstile antenna
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The name reflects the notion the antenna looks like a turnstile when mounted horizontally. The antenna can be used in two possible modes, in normal mode the antenna radiates horizontally polarized radio waves perpendicular to its axis. In axial mode the antenna radiates circularly polarized radiation along its axis, specialized normal mode turnstile antennas called superturnstile or batwing antennas are used as television broadcasting antennas. The turnstile antenna was invented by George Brown in 1935 and described in scholarship in 1936, the patent history reveals the popularity of the turnstile antenna over the years. The antenna can be used in two different modes, normal mode and axial mode, in directions perpendicular to its axis the antenna radiates linearly polarized radio waves. The radiation pattern, a superposition of the two patterns, is close to omnidirectional but actually cloverleaf shaped, with four small maxima off the ends of the elements. The pattern departs from omnidirectional by only ±5 percent, the radiation in these horizontal directions is often increased by vertically stacking multiple turnstile antennas fed in phase. These stacked normal mode turnstile antennas are used at VHF and UHF frequencies for FM, since the first turnstiles invented by Brown operated in this mode, the normal mode turnstile is occasionally called the George Brown turnstile antenna. Off the ends of the axis, perpendicular to the plane of the elements. The radiation off one end is righthand-circularly-polarized and the end is lefthand-circularly-polarized. Which end produces which polarization is determined by the phase of the feed connections, the waves in that direction are reflected back 180° and the reflection reverses the polarization sense, so the reflected waves reinforce the forward radiation. For example, if the waves radiated forward are right-circularly-polarized. The flat reflector reverses the sense so the reflected waves are right-circularly-polarized. By locating the reflector λ/4 behind the elements the direct and reflected waves are in phase, addition of the reflector increases the axial radiation by a factor of 2. Another common way to increase the axial mode radiation is to replace each dipole with a Yagi array, axial mode turnstile antennas are often used for satellite and missile antennas, since circular polarization is used in satellite communication. This is because with circularly polarized waves the relative orientation of the antenna elements does not affect the gain, the fundamental requirement for the turnstile to function is ensuring each dipoles currents are of equal magnitude and in phase quadrature. This is done with feed-line techniques or by adding reactance in series with the dipoles, each phase is applied to one of the dipoles. By modifying the length and shape of the dipoles, the combined terminal impedance presented to a single feed-point can achieve pure resistance and this method of changing the physical dimensions of the antenna element to yield quadrature currents is known as turnstile feeding
11.
T-antenna
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A T-antenna, T-aerial, flat-top antenna, or top-hat antenna is a vertically polarized simple wire radio antenna used in the VLF, LF, MF and shortwave bands. T-antennas are widely used as transmitting antennas for radio stations, long wave. They are also used as receiving antennas for shortwave listening, the antenna consists of one or more horizontal wires suspended between two supporting radio masts or buildings and insulated from them at the ends. A vertical wire is connected to the center of the wires and hangs down close to the ground. Combined, the two form a T shape, hence the name. The transmitter power is applied, or the receiver is connected, the T-antenna functions as a monopole antenna with capacitive top-loading, other antennas in this category include the inverted-L, umbrella, delta, and triatic antennas. It was invented during the first decades of radio, in the wireless telegraphy era, instead it serves to add capacitance to the top of the antenna. The top load wire can increase radiated power by 2 to 4 times for a given base current, however, the antenna is still typically not as efficient as a full-height λ/4 vertical monopole, and has a higher Q and thus a narrower bandwidth. 1λ or less. Since the radiation resistance and efficiency increases with height, the antenna should be suspended as high as possible, the antenna has a base impedance with a capacitive component that must be tuned out with an added inductor. To increase the capacitance, several parallel horizontal wires are often used, connected together at the center where the vertical wire attaches. The capacitance does not increase proportionally with the number of wires, however, since the vertical wire is the actual radiating element, the antenna radiates vertically polarized radio waves in an omnidirectional radiation pattern, with equal power in all azimuthal directions. The axis of the horizontal wire makes little difference, the power is maximum in a horizontal direction or at a shallow elevation angle, decreasing to zero at the zenith. The effect of ground conductivity is generally to tilt the pattern up. Since it is shorter than λ/4 the T antenna has a capacitive reactance. To operate over a frequency range the loading coil often must be adjustable. The high Q also causes a voltage on the antenna. The insulators at the ends must be designed to withstand these voltages, in high power transmitters the output power is often limited by the onset of corona discharge on the wires. At low frequencies the resistance is very low, often less than an ohm
This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C".
