1.
Transmission line
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This article covers two-conductor transmission line such as parallel line, coaxial cable, stripline, and microstrip. Ordinary electrical cables suffice to carry low frequency alternating current, such as power, which reverses direction 100 to 120 times per second. However, they cannot be used to carry currents in the frequency range, above about 30 kHz, because the energy tends to radiate off the cable as radio waves. Radio frequency currents tend to reflect from discontinuities in the cable such as connectors and joints. These reflections act as bottlenecks, preventing the signal power from reaching the destination, Transmission lines use specialized construction, and impedance matching, to carry electromagnetic signals with minimal reflections and power losses. Types of transmission line include parallel line, coaxial cable, and planar transmission lines such as stripline, the higher the frequency of electromagnetic waves moving through a given cable or medium, the shorter the wavelength of the waves. Transmission lines become necessary when the length of the cable is longer than a significant fraction of the transmitted frequencys wavelength. At microwave frequencies and above, power losses in transmission lines become excessive, and waveguides are used instead, some sources define waveguides as a type of transmission line, however, this article will not include them. At even higher frequencies, in the terahertz, infrared and light range, waveguides in turn become lossy, mathematical analysis of the behaviour of electrical transmission lines grew out of the work of James Clerk Maxwell, Lord Kelvin and Oliver Heaviside. In 1855 Lord Kelvin formulated a model of the current in a submarine cable. The model correctly predicted the performance of the 1858 trans-Atlantic submarine telegraph cable. In 1885 Heaviside published the first papers that described his analysis of propagation in cables, in many electric circuits, the length of the wires connecting the components can for the most part be ignored. That is, the voltage on the wire at a time can be assumed to be the same at all points. Stated another way, the length of the wire is important when the signal frequency components with corresponding wavelengths comparable to or less than the length of the wire. A common rule of thumb is that the cable or wire should be treated as a line if the length is greater than 1/10 of the wavelength. If the transmission line is uniform along its length, then its behaviour is described by a single parameter called the characteristic impedance. This is the ratio of the voltage of a given wave to the complex current of the same wave at any point on the line. Typical values of Z0 are 50 or 75 ohms for a cable, about 100 ohms for a twisted pair of wires
2.
Phasor
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In physics and engineering, a phasor, is a complex number representing a sinusoidal function whose amplitude, angular frequency, and initial phase are time-invariant. The complex constant, which encapsulates amplitude and phase dependence, is known as phasor, complex amplitude, a common situation in electrical networks is the existence of multiple sinusoids all with the same frequency, but different amplitudes and phases. The only difference in their analytic representations is the complex amplitude, a linear combination of such functions can be factored into the product of a linear combination of phasors and the time/frequency dependent factor that they all have in common. The origin of the term phasor rightfully suggests that a somewhat similar to that possible for vectors is possible for phasors as well. The originator of the phasor transform was Charles Proteus Steinmetz working at General Electric in the late 19th century, however, the Laplace transform is mathematically more difficult to apply and the effort may be unjustified if only steady state analysis is required. The function A ⋅ e i is the representation of A ⋅ cos . Figure 2 depicts it as a vector in a complex plane. It is sometimes convenient to refer to the function as a phasor. But the term usually implies just the static vector, A e i θ. An even more compact representation of a phasor is the angle notation, multiplication of the phasor A e i θ e i ω t by a complex constant, B e i ϕ, produces another phasor. That means its only effect is to change the amplitude and phase of the underlying sinusoid, Re = Re = A B cos In electronics, B e i ϕ would represent an impedance, in particular it is not the shorthand notation for another phasor. Multiplying a phasor current by an impedance produces a phasor voltage, but the product of two phasors would represent the product of two sinusoids, which is a non-linear operation that produces new frequency components. Phasor notation can only represent systems with one frequency, such as a linear system stimulated by a sinusoid, the time derivative or integral of a phasor produces another phasor. For example, Re = Re = Re = Re = ω A ⋅ cos Therefore, in phasor representation, similarly, integrating a phasor corresponds to multiplication by 1 i ω = e − i π /2 ω. The time-dependent factor, e i ω t, is unaffected, when we solve a linear differential equation with phasor arithmetic, we are merely factoring e i ω t out of all terms of the equation, and reinserting it into the answer. In polar coordinate form, it is,11 +2 ⋅ e − i ϕ, Therefore, v C =11 +2 ⋅ V P cos The sum of multiple phasors produces another phasor. A key point is that A3 and θ3 do not depend on ω or t, the time and frequency dependence can be suppressed and re-inserted into the outcome as long as the only operations used in between are ones that produce another phasor. In angle notation, the operation shown above is written, A1 ∠ θ1 + A2 ∠ θ2 = A3 ∠ θ3, another way to view addition is that two vectors with coordinates and are added vectorially to produce a resultant vector with coordinates
3.
Voltage
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Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential energy between two points per unit electric charge. The voltage between two points is equal to the work done per unit of charge against an electric field to move the test charge between two points. This is measured in units of volts, voltage can be caused by static electric fields, by electric current through a magnetic field, by time-varying magnetic fields, or some combination of these three. A voltmeter can be used to measure the voltage between two points in a system, often a reference potential such as the ground of the system is used as one of the points. A voltage may represent either a source of energy or lost, used, given two points in space, x A and x B, voltage is the difference in electric potential between those two points. Electric potential must be distinguished from electric energy by noting that the potential is a per-unit-charge quantity. Like mechanical potential energy, the zero of electric potential can be chosen at any point, so the difference in potential, i. e. the voltage, is the quantity which is physically meaningful. The voltage between point A to point B is equal to the work which would have to be done, per unit charge, against or by the electric field to move the charge from A to B. The voltage between the two ends of a path is the energy required to move a small electric charge along that path. Mathematically this is expressed as the integral of the electric field. In the general case, both an electric field and a dynamic electromagnetic field must be included in determining the voltage between two points. Historically this quantity has also called tension and pressure. Pressure is now obsolete but tension is used, for example within the phrase high tension which is commonly used in thermionic valve based electronics. Voltage is defined so that negatively charged objects are pulled towards higher voltages, therefore, the conventional current in a wire or resistor always flows from higher voltage to lower voltage. Current can flow from lower voltage to higher voltage, but only when a source of energy is present to push it against the electric field. This is the case within any electric power source, for example, inside a battery, chemical reactions provide the energy needed for ion current to flow from the negative to the positive terminal. The electric field is not the only factor determining charge flow in a material, the electric potential of a material is not even a well defined quantity, since it varies on the subatomic scale. A more convenient definition of voltage can be found instead in the concept of Fermi level, in this case the voltage between two bodies is the thermodynamic work required to move a unit of charge between them
4.
Electrical network
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An electrical network is an interconnection of electrical components or a model of such an interconnection, consisting of electrical elements. An electrical circuit is a network consisting of a closed loop, linear electrical networks, a special type consisting only of sources, linear lumped elements, and linear distributed elements, have the property that signals are linearly superimposable. They are thus more easily analyzed, using powerful frequency domain methods such as Laplace transforms, to determine DC response, AC response, a resistive circuit is a circuit containing only resistors and ideal current and voltage sources. Analysis of resistive circuits is less complicated than analysis of circuits containing capacitors and inductors, if the sources are constant sources, the result is a DC circuit. A network that contains active components is known as an electronic circuit. Such networks are generally nonlinear and require more complex design and analysis tools, an active network is a network that contains an active source – either a voltage source or current source. A passive network is a network that does not contain an active source, a network is linear if its signals obey the principle of superposition, otherwise it is non-linear. Sources can be classified as independent sources and dependent sources Ideal Independent Source maintains same voltage or current regardless of the elements present in the circuit. Its value is either constant or sinusoidal, the strength of voltage or current is not changed by any variation in connected network. Dependent Sources depend upon a particular element of the circuit for delivering the power or voltage or current depending upon the type of source it is, a number of electrical laws apply to all electrical networks. These include, Kirchhoffs current law, The sum of all currents entering a node is equal to the sum of all currents leaving the node, Kirchhoffs voltage law, The directed sum of the electrical potential differences around a loop must be zero. Ohms law, The voltage across a resistor is equal to the product of the resistance, nortons theorem, Any network of voltage or current sources and resistors is electrically equivalent to an ideal current source in parallel with a single resistor. Thévenins theorem, Any network of voltage or current sources and resistors is electrically equivalent to a voltage source in series with a single resistor. Other more complex laws may be needed if the network contains nonlinear or reactive components, non-linear self-regenerative heterodyning systems can be approximated. Applying these laws results in a set of equations that can be solved either algebraically or numerically. To design any electrical circuit, either analog or digital, electrical engineers need to be able to predict the voltages, simple linear circuits can be analyzed by hand using complex number theory. In more complex cases the circuit may be analyzed with specialized programs or estimation techniques such as the piecewise-linear model. More complex circuits can be analyzed numerically with software such as SPICE or GNUCAP, once the steady state solution is found, the operating points of each element in the circuit are known
5.
Electrical load
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An electrical load is an electrical component or portion of a circuit that consumes electric power. This is opposed to a source, such as a battery or generator. In electric power circuits examples of loads are appliances and lights, the term may also refer to the power consumed by a circuit. The term is used broadly in electronics for a device connected to a signal source. If an electric circuit has a port, a pair of terminals that produces an electrical signal. For example, if a CD player is connected to an amplifier, the CD player is the source, load affects the performance of circuits with respect to output voltages or currents, such as in sensors, voltage sources, and amplifiers. Mains power outlets provide an example, they supply power at constant voltage. When a high-power appliance switches on, it reduces the load impedance. If the load impedance is not very much higher than the power supply impedance, in a domestic environment, switching on a heating appliance may cause incandescent lights to dim noticeably. When discussing the effect of load on a circuit, it is helpful to disregard the circuits actual design and consider only the Thévenin equivalent. The Thévenin equivalent of a circuit looks like this, With no load, all of V S falls across the output, the voltage is V S. However. We would like to ignore the details of the circuit, as we did for the power supply. This current places a voltage drop across R S, so the voltage at the terminal is no longer V S. This illustration uses simple resistances, but similar discussion can be applied in alternating current circuits using resistive, capacitive and inductive elements
6.
Reflections of signals on conducting lines
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This can happen, for instance, if two lengths of dissimilar transmission lines are joined together. This article is about signal reflections on electrically conducting lines, such lines are loosely referred to as copper lines, and indeed, in telecommunications are generally made from copper, but other metals are used, notably aluminium in power lines. Reflections cause several undesirable effects, including modifying frequency responses, causing overload power in transmitters, however, the reflection phenomenon can also be made use of in such devices as stubs and impedance transformers. The special cases of open circuit and short circuit lines are of relevance to stubs. Reflections cause standing waves to be set up on the line, conversely, standing waves are an indication that reflections are present. There is a relationship between the measures of reflection coefficient and standing wave ratio, there are several approaches to understanding reflections, but the relationship of reflections to the conservation laws is particularly enlightening. A simple example is a voltage, V u, applied to one end of a lossless line. It cannot have any effect until the step actually reaches that point, the signal cannot have any foreknowledge of what is at the end of the line and is only affected by the local characteristics of the line. However, if the line is of length l the step will arrive at the circuit at time t = l / κ. Essentially, this is Kirchhoffs current law in operation and this equal and opposite current is the reflected current, i r, and since i r = v r Z0 there must also be a reflected voltage, v r, to drive the reflected current down the line. This reflected voltage must exist by reason of conservation of energy, the source is supplying energy to the line at a rate of v i i i. None of this energy is dissipated in the line or its termination, the only available direction is back up the line. As the reflection proceeds back up the line the reflected voltage continues to add to the incident voltage, if the generator is matched to the line with an impedance of Z0 the step transient will be absorbed in the generator internal impedance and there will be no further reflections. This counter-intuitive doubling of voltage may become clearer if the voltages are considered when the line is so short that it can be ignored for the purposes of analysis. The equivalent circuit of a generator matched to a load Z0 to which it is delivering a voltage V can be represented as in figure 2. That is, the generator can be represented as an ideal voltage generator of twice the voltage it is to deliver, however, if the generator is left open circuit, a voltage of 2 V appears at the generator output terminals as in figure 3. The same situation pertains if a short transmission line is inserted between the generator and the open circuit. But after an interval, a reflected transient will return from the end of the line with the information on what the line is terminated with
7.
Input impedance
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The input impedance of an electrical network is the measure of the opposition to current flow, both static and dynamic, into the load network being connected that is external to the electrical source. The input admittance is a measure of the propensity to draw current. The source network is the portion of the network that transmits power, and so the voltage across and current through the input terminals would be identical to the original load network. The Thévenins equivalent circuit of the network uses the concept of input impedance to determine the impedance of the equivalent circuit. To calculate the impedance, short the input terminals together. In this case, Z i n ≫ Z o u t The input impedance of the stage is much larger than the output impedance of the source. In AC circuits carrying power, the due to the reactive component of the impedance can be significant. These losses manifest themselves in a phenomenon called phase imbalance, where the current is out of phase with the voltage, therefore, the product of the current and the voltage is less than what it would be if the current and voltage were in phase. With DC sources, reactive circuits have no impact, therefore power factor correction is not necessary. For a circuit modeled with a source, an output impedance, and an input impedance. In this scenario the reactive component of the input impedance cancels the reactive component of the impedance of the load. From the ideal sources perspective the circuit between the output and input impedance is purely resistive in nature, and there are no losses due to imbalance in the source or the load. Z i n = X − j Im The maximum power will be transferred when the resistance of the source is equal to the resistance of the load, when this occurs the circuit is said to be complex conjugate matched to the signals impedance. Note this only maximizes the transfer, not the efficiency of the circuit. When the power transfer is optimized the circuit runs at 50% efficiency. Also note that equation does not work in reverse, the optimal output impedance of the source is 0 regardless of the input impedance of the load. The formula for complex conjugate matched is Z i n = Z o u t ∗ = | Z o u t | e − Θ o u t j = Re − Im j. When there is no reactive component this equation simplifies to Z i n = Z o u t as the part of Z o u t is zero
8.
International System of Units
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The International System of Units is the modern form of the metric system, and is the most widely used system of measurement. It comprises a coherent system of units of measurement built on seven base units, the system also establishes a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. The system was published in 1960 as the result of an initiative began in 1948. It is based on the system of units rather than any variant of the centimetre-gram-second system. The motivation for the development of the SI was the diversity of units that had sprung up within the CGS systems, the International System of Units has been adopted by most developed countries, however, the adoption has not been universal in all English-speaking countries. The metric system was first implemented during the French Revolution with just the metre and kilogram as standards of length, in the 1830s Carl Friedrich Gauss laid the foundations for a coherent system based on length, mass, and time. In the 1860s a group working under the auspices of the British Association for the Advancement of Science formulated the requirement for a coherent system of units with base units and derived units. Meanwhile, in 1875, the Treaty of the Metre passed responsibility for verification of the kilogram, in 1921, the Treaty was extended to include all physical quantities including electrical units originally defined in 1893. The units associated with these quantities were the metre, kilogram, second, ampere, kelvin, in 1971, a seventh base quantity, amount of substance represented by the mole, was added to the definition of SI. On 11 July 1792, the proposed the names metre, are, litre and grave for the units of length, area, capacity. The committee also proposed that multiples and submultiples of these units were to be denoted by decimal-based prefixes such as centi for a hundredth, on 10 December 1799, the law by which the metric system was to be definitively adopted in France was passed. Prior to this, the strength of the magnetic field had only been described in relative terms. The technique used by Gauss was to equate the torque induced on a magnet of known mass by the earth’s magnetic field with the torque induced on an equivalent system under gravity. The resultant calculations enabled him to assign dimensions based on mass, length, a French-inspired initiative for international cooperation in metrology led to the signing in 1875 of the Metre Convention. Initially the convention only covered standards for the metre and the kilogram, one of each was selected at random to become the International prototype metre and International prototype kilogram that replaced the mètre des Archives and kilogramme des Archives respectively. Each member state was entitled to one of each of the prototypes to serve as the national prototype for that country. Initially its prime purpose was a periodic recalibration of national prototype metres. The official language of the Metre Convention is French and the version of all official documents published by or on behalf of the CGPM is the French-language version
9.
Electrical impedance
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Electrical impedance is the measure of the opposition that a circuit presents to a current when a voltage is applied. In quantitative terms, it is the ratio of the voltage to the current in an alternating current circuit. Impedance extends the concept of resistance to AC circuits, and possesses both magnitude and phase, unlike resistance, which has only magnitude. When a circuit is driven with direct current, there is no distinction between impedance and resistance, the latter can be thought of as impedance with zero phase angle. The impedance caused by two effects is collectively referred to as reactance and forms the imaginary part of complex impedance whereas resistance forms the real part. The symbol for impedance is usually Z and it may be represented by writing its magnitude, however, cartesian complex number representation is often more powerful for circuit analysis purposes. The term impedance was coined by Oliver Heaviside in July 1886, arthur Kennelly was the first to represent impedance with complex numbers in 1893. Impedance is defined as the frequency ratio of the voltage to the current. In other words, it is the voltage–current ratio for a complex exponential at a particular frequency ω. In general, impedance will be a number, with the same units as resistance. For a sinusoidal current or voltage input, the form of the complex impedance relates the amplitude and phase of the voltage. In particular, The magnitude of the impedance is the ratio of the voltage amplitude to the current amplitude. The phase of the impedance is the phase shift by which the current lags the voltage. The reciprocal of impedance is admittance, Impedance is represented as a complex quantity Z and the term complex impedance may be used interchangeably. J is the unit, and is used instead of i in this context to avoid confusion with the symbol for electric current. In Cartesian form, impedance is defined as Z = R + j X where the part of impedance is the resistance R. Where it is needed to add or subtract impedances, the form is more convenient, but when quantities are multiplied or divided. A circuit calculation, such as finding the total impedance of two impedances in parallel, may require conversion between forms several times during the calculation, conversion between the forms follows the normal conversion rules of complex numbers
10.
Ohm
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The ohm is the SI derived unit of electrical resistance, named after German physicist Georg Simon Ohm. The definition of the ohm was revised several times, today the definition of the ohm is expressed from the quantum Hall effect. In many cases the resistance of a conductor in ohms is approximately constant within a range of voltages, temperatures. In alternating current circuits, electrical impedance is also measured in ohms, the siemens is the SI derived unit of electric conductance and admittance, also known as the mho, it is the reciprocal of resistance in ohms. The power dissipated by a resistor may be calculated from its resistance, non-linear resistors have a value that may vary depending on the applied voltage. The rapid rise of electrotechnology in the last half of the 19th century created a demand for a rational, coherent, consistent, telegraphers and other early users of electricity in the 19th century needed a practical standard unit of measurement for resistance. Two different methods of establishing a system of units can be chosen. Various artifacts, such as a length of wire or a standard cell, could be specified as producing defined quantities for resistance, voltage. This latter method ensures coherence with the units of energy, defining a unit for resistance that is coherent with units of energy and time in effect also requires defining units for potential and current. Some early definitions of a unit of resistance, for example, the absolute-units system related magnetic and electrostatic quantities to metric base units of mass, time, and length. These units had the advantage of simplifying the equations used in the solution of electromagnetic problems. However, the CGS units turned out to have impractical sizes for practical measurements, various artifact standards were proposed as the definition of the unit of resistance. In 1860 Werner Siemens published a suggestion for a reproducible resistance standard in Poggendorffs Annalen der Physik und Chemie and he proposed a column of pure mercury, of one square millimetre cross section, one metre long, Siemens mercury unit. However, this unit was not coherent with other units, one proposal was to devise a unit based on a mercury column that would be coherent – in effect, adjusting the length to make the resistance one ohm. Not all users of units had the resources to carry out experiments to the required precision. The BAAS in 1861 appointed a committee including Maxwell and Thomson to report upon Standards of Electrical Resistance, in the third report of the committee,1864, the resistance unit is referred to as B. A. unit, or Ohmad. By 1867 the unit is referred to as simply Ohm, the B. A. ohm was intended to be 109 CGS units but owing to an error in calculations the definition was 1. 3% too small. The error was significant for preparation of working standards, on September 21,1881 the Congrès internationale délectriciens defined a practical unit of Ohm for the resistance, based on CGS units, using a mercury column at zero deg
11.
Telegrapher's equations
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The telegraphers equations are a pair of coupled, linear differential equations that describe the voltage and current on an electrical transmission line with distance and time. The equations come from Oliver Heaviside who in the 1880s developed the line model. The model demonstrates that the waves can be reflected on the wire. The theory applies to transmission lines of all frequencies including high-frequency transmission lines, audio frequency, low frequency, the telegraphers equations, like all other equations describing electrical phenomena, result from Maxwells equations. The distributed inductance L is represented by a series inductor, the capacitance C between the two conductors is represented by a shunt capacitor C. The conductance G of the material separating the two conductors is represented by a shunt resistor between the signal wire and the return wire. This resistor in the model has a resistance of 1 / G ohms, an alternative notation is to use R ′, L ′, C ′, and G ′ to emphasize that the values are derivatives with respect to length. All these constants are constant with respect to time, voltage and they may be non-constant functions of frequency. The role of the different components can be visualized based on the animation at right, the inductance L makes it look like the electrons have inertia, i. e. with a large inductance, it is difficult to increase or decrease the current flow at any given point. Large inductance makes the move more slowly, just as waves travel more slowly down a heavy rope than a light one. It also gives it a higher impedance, the capacitance C controls how much the bunched-up electrons repel each other, and conversely how much the spread-out electrons attract each other. With a large capacitance, there is less attraction and repulsion, large capacitance makes the wave move more slowly, and also gives it a lower impedance. R corresponds to resistance within each line, and G allows current to flow from one line to the other, the figure at right shows a lossless transmission line, where both R and G are 0. Representative parameter data for 24 gauge telephone polyethylene insulated cable at 70 °F More extensive tables and tables for other gauges, temperatures and types are available in Reeve, Chen gives the same data in a parameterized form that he states is usable up to 50 MHz. The variation of R and L is mainly due to skin effect, the constancy of the capacitance is a consequence of intentional design. The variation of G can be inferred from Terman The power factor, tends to be independent of frequency, since the fraction of energy lost during each cycle. Is substantially independent of the number of cycles per second, over wide frequency ranges, a function of the form G = G1 g e with ge close to 1.0 would fit the statement from Terman. Chen gives an equation of similar form, in practice, before that point is reached, a transmission line with a better dielectric is used
12.
Series and parallel circuits
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Components of an electrical circuit or electronic circuit can be connected in many different ways. The two simplest of these are called series and parallel and occur frequently, components connected in series are connected along a single path, so the same current flows through all of the components. Components connected in parallel are connected, so the voltage is applied to each component. A circuit composed solely of components connected in series is known as a circuit, likewise. In a series circuit, the current through each of the components is the same, in a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents through each component. Consider a very simple circuit consisting of four light bulbs and one 6 V battery. If a wire joins the battery to one bulb, to the bulb, to the next bulb, to the next bulb, then back to the battery, in one continuous loop. If each bulb is wired to the battery in a separate loop, the bulbs are said to be in parallel. If the four light bulbs are connected in series, there is current through all of them, and the voltage drop is 1.5 V across each bulb. If the light bulbs are connected in parallel, the currents through the light bulbs combine to form the current in the battery, while the drop is across each bulb. In a series circuit, every device must function for the circuit to be complete, one bulb burning out in a series circuit breaks the circuit. In parallel circuits, each light has its own circuit, so all but one light could be burned out, Series circuits are sometimes called current-coupled or daisy chain-coupled. The current in a series circuit goes through every component in the circuit, therefore, all of the components in a series connection carry the same current. There is only one path in a circuit in which the current can flow. For example, if one of the light bulbs in an older-style string of Christmas tree lights burns out or is removed. = I n In a series circuit the current is the same for all of elements. The total resistance of resistors in series is equal to the sum of their individual resistances, R total = R1 + R2 + ⋯ + R n Electrical conductance presents a reciprocal quantity to resistance. Total conductance of a series circuits of pure resistors, therefore, for a special case of two resistors in series, the total conductance is equal to, G total = G1 G2 G1 + G2
13.
Inductance
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According to Lenzs law, a changing electric current through a circuit that contains inductance induces a proportional voltage, which opposes the change in current. The varying field in this circuit may also induce an EMF in neighbouring circuits, the term inductance was coined by Oliver Heaviside in 1886. It is customary to use the symbol L for inductance, in honour of the physicist Heinrich Lenz. In the SI system, the measurement unit for inductance is the henry, with the unit symbol H, named in honor of Joseph Henry, who discovered inductance independently of, an electronic component that is intended to add inductance to a circuit is called an inductor. Inductors are typically manufactured from coils of wire and this design delivers two desired properties, a concentration of the magnetic field into a small physical space and a linking of the magnetic field into the circuit multiple times. The relationship between the self-inductance, L, of a circuit, the voltage, v. A voltage is induced across an inductor, that is equal to the product of the inductors inductance, all circuits have, in practice, some inductance, which may have beneficial or detrimental effects. For a tuned circuit, inductance is used to provide a frequency-selective circuit, practical inductors may be used to provide filtering, or energy storage, in a given network. The inductance of long AC power transmission lines affects the power capacity of the line, sensitive circuits, such as microphone and computer network cables, may utilize special cabling construction, limiting the inductive coupling between circuits. The generalization to the case of K electrical circuits with currents, here, inductance L is a symmetric matrix. The diagonal coefficients Lm, m are called coefficients of self-inductance, the coefficients of inductance are constant, as long as no magnetizable material with nonlinear characteristics is involved. This is a consequence of the linearity of Maxwells equations in the fields. The coefficients of inductance become functions of the currents in the nonlinear case, the inductance equations above are a consequence of Maxwells equations. There is a derivation in the important case of electrical circuits consisting of thin wires. Here Nm denotes the number of turns in loop m, Φm, the flux through loop m. This equation follows from Amperes law - magnetic fields and fluxes are linear functions of the currents and this agrees with the definition of inductance above if the coefficients Lm, n are identified with the coefficients of inductance. Because the total currents Nnin contribute to Φm it also follows that Lm, ∑ n =1 K ∂ W ∂ i n d i n. This must agree with the change of the field energy, W
14.
Electrical resistance and conductance
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The electrical resistance of an electrical conductor is a measure of the difficulty to pass an electric current through that conductor. The inverse quantity is electrical conductance, and is the ease with which a current passes. Electrical resistance shares some parallels with the notion of mechanical friction. The SI unit of resistance is the ohm, while electrical conductance is measured in siemens. An object of uniform cross section has a proportional to its resistivity and length. All materials show some resistance, except for superconductors, which have a resistance of zero and this proportionality is called Ohms law, and materials that satisfy it are called ohmic materials. In other cases, such as a diode or battery, V and I are not directly proportional. The ratio V/I is sometimes useful, and is referred to as a chordal resistance or static resistance, since it corresponds to the inverse slope of a chord between the origin and an I–V curve. In other situations, the derivative d V d I may be most useful, in the hydraulic analogy, current flowing through a wire is like water flowing through a pipe, and the voltage drop across the wire is like the pressure drop that pushes water through the pipe. Conductance is proportional to how much flow occurs for a given pressure, the voltage drop, not the voltage itself, provides the driving force pushing current through a resistor. In hydraulics, it is similar, The pressure difference between two sides of a pipe, not the pressure itself, determines the flow through it, for example, there may be a large water pressure above the pipe, which tries to push water down through the pipe. But there may be a large water pressure below the pipe. If these pressures are equal, no water flows, in the same way, a long, thin copper wire has higher resistance than a short, thick copper wire. A pipe filled with hair restricts the flow of more than a clean pipe of the same shape. The difference between copper, steel, and rubber is related to their structure and electron configuration. In addition to geometry and material, there are other factors that influence resistance and conductance, such as temperature. Substances in which electricity can flow are called conductors, a piece of conducting material of a particular resistance meant for use in a circuit is called a resistor. Conductors are made of high-conductivity materials such as metals, in particular copper, Resistors, on the other hand, are made of a wide variety of materials depending on factors such as the desired resistance, amount of energy that it needs to dissipate, precision, and costs
15.
Capacitance
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Capacitance is the ability of a body to store an electric charge. There are two related notions of capacitance--self capacitance and mutual capacitance--that are usually both designated by the same term, capacitance. Any object that can be electrically charged exhibits self capacitance, a material with a large self capacitance holds more electric charge at a given voltage, than one with low capacitance. The notion of mutual capacitance is important for understanding the operations of the capacitor. The capacitance is a function only of the geometry of the design, for many dielectric materials, the permittivity and thus the capacitance, is independent of the potential difference between the conductors and the total charge on them. The SI unit of capacitance is the farad, named after the English physicist Michael Faraday, a 1 farad capacitor, when charged with 1 coulomb of electrical charge, has a potential difference of 1 volt between its plates. In electrical circuits, the capacitance is usually a shorthand for the mutual capacitance between two adjacent conductors, such as the two plates of a capacitor. It is actually mutual capacitance between the turns of the coil and is a form of stray, or parasitic capacitance. This self-capacitance is an important consideration at high frequencies and it changes the impedance of the coil and gives rise to parallel resonance. In many applications this is an effect and sets an upper frequency limit for the correct operation of the circuit. The inverse of capacitance is called elastance, the unit of elastance is the daraf, but is not recognised by SI. A common form is a capacitor, which consists of two conductive plates insulated from each other, usually sandwiching a dielectric material. In a parallel capacitor, capacitance is very nearly proportional to the surface area of the conductor plates. If the charges on the plates are +q and −q, and V gives the voltage between the plates, then the capacitance C is given by C = q V. which gives the voltage/current relationship I = C d V d t. Historically, a farad was regarded as a large unit. Its subdivisions were invariably used, namely the microfarad, nanofarad and picofarad, more recently, technology has advanced such that capacitors of 1 farad and greater can be constructed in a structure little larger than a coin battery. Such capacitors are used for energy storage replacing more traditional batteries. The energy stored in a capacitor is found by integrating the work W, W charging =12 C V2 The discussion above is limited to the case of two conducting plates, although of arbitrary size and shape
16.
Imaginary unit
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The imaginary unit or unit imaginary number is a solution to the quadratic equation x2 +1 =0. The term imaginary is used there is no real number having a negative square. There are two square roots of −1, namely i and −i, just as there are two complex square roots of every real number other than zero, which has one double square root. In contexts where i is ambiguous or problematic, j or the Greek ι is sometimes used, in the disciplines of electrical engineering and control systems engineering, the imaginary unit is normally denoted by j instead of i, because i is commonly used to denote electric current. For the history of the unit, see Complex number § History. The imaginary number i is defined solely by the property that its square is −1, with i defined this way, it follows directly from algebra that i and −i are both square roots of −1. In polar form, i is represented as 1eiπ/2, having a value of 1. In the complex plane, i is the point located one unit from the origin along the imaginary axis, more precisely, once a solution i of the equation has been fixed, the value −i, which is distinct from i, is also a solution. Since the equation is the definition of i, it appears that the definition is ambiguous. However, no ambiguity results as long as one or other of the solutions is chosen and labelled as i and this is because, although −i and i are not quantitatively equivalent, there is no algebraic difference between i and −i. Both imaginary numbers have equal claim to being the number whose square is −1, the issue can be a subtle one. See also Complex conjugate and Galois group, a more precise explanation is to say that the automorphism group of the special orthogonal group SO has exactly two elements — the identity and the automorphism which exchanges CW and CCW rotations. All these ambiguities can be solved by adopting a rigorous definition of complex number. For example, the pair, in the usual construction of the complex numbers with two-dimensional vectors. The imaginary unit is sometimes written √−1 in advanced mathematics contexts, however, great care needs to be taken when manipulating formulas involving radicals. The radical sign notation is reserved either for the square root function. Similarly,1 i =1 −1 =1 −1 = −11 = −1 = i, the calculation rules a ⋅ b = a ⋅ b and a b = a b are only valid for real, non-negative values of a and b. These problems are avoided by writing and manipulating expressions like i√7, for a more thorough discussion, see Square root and Branch point
17.
Dielectric loss
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Dielectric loss quantifies a dielectric materials inherent dissipation of electromagnetic energy. It can be parameterized in terms of either the loss angle δ or the loss tangent tan δ. Both refer to the phasor in the plane whose real and imaginary parts are the resistive component of an electromagnetic field. Maxwell’s equations are solved for the electric and magnetic components of the propagating waves that satisfy the boundary conditions of the specific environments geometry. In such electromagnetic analyses, the parameters permittivity ε, permeability μ, the permittivity can have real and imaginary components such that ε = ε ′ − j ε ″. The component ε′ represents the familiar lossless permittivity given by the product of the free space permittivity and the relative real permittivity, or ε′ = ε0ε′r. The loss tangent is then defined as the ratio of the reaction to the electric field E in the curl equation to the lossless reaction. For dielectrics with small loss, this angle is ≪1 and tan δ ≈ δ. Also, a similar analysis could be applied to the magnetic permeability where μ = μ ′ − j μ ″, the electric loss tangent can be similarly defined, tan δ e = ε ″ ε ′, upon introduction of an effective dielectric conductivity. For discrete electrical circuit components, a capacitor is made of a dielectric placed between conductors. The lumped element model of a capacitor includes an ideal capacitor in series with a resistor termed the equivalent series resistance. The ESR represents losses in the capacitor, in a low-loss capacitor the ESR is very small, and in a lossy capacitor the ESR can be large. Note that the ESR is not simply the resistance that would be measured across a capacitor by an ohmmeter, the ESR is a derived quantity representing the loss due to both the dielectrics conduction electrons and the bound dipole relaxation phenomena mentioned above. In a dielectric, one of the electrons or the dipole relaxation typically dominates loss in a particular dielectric. For the case of the electrons being the dominant loss, then E S R = σ ε ′ ω2 C. The loss tangent is then tan δ = E S R | X c | = ω C ⋅ E S R = σ ε ′ ω. Since the same AC current flows through both ESR and Xc, the tangent is also the ratio of the resistive power loss in the ESR to the reactive power oscillating in the capacitor. For this reason, a capacitors loss tangent is sometimes stated as its dissipation factor, or the reciprocal of its quality factor Q, as follows tan δ = D F =1 Q
18.
Electric power transmission
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Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. The interconnected lines which facilitate this movement are known as a transmission network and this is distinct from the local wiring between high-voltage substations and customers, which is typically referred to as electric power distribution. The combined transmission and distribution network is known as the grid in North America. In the United Kingdom, the network is known as the National Grid, for example, there are four major interconnections in North America, and one large grid for most of continental Europe. Most transmission lines are high-voltage three-phase alternating current, although single phase AC is sometimes used in railway electrification systems, high-voltage direct-current technology is used for greater efficiency over very long distances. HVDC technology is used in submarine power cables, and in the interchange of power between grids that are not mutually synchronized. HVDC links are used to large power distribution networks where sudden new loads, or blackouts, in one part of a network can result in synchronization problems. Electricity is transmitted at high voltages to reduce the loss which occurs in long-distance transmission. Power is usually transmitted through overhead power lines, underground power transmission has a significantly higher installation cost and greater operational limitations, but reduced maintenance costs. Underground transmission is used in urban areas or environmentally sensitive locations. A lack of energy storage facilities in transmission systems leads to a key limitation. Electrical energy must be generated at the rate at which it is consumed. A sophisticated control system is required to ensure that the power generation very closely matches the demand, if the demand for power exceeds supply, the imbalance can cause generation plant and transmission equipment to automatically disconnect and/or shut down to prevent damage. In the worst case, this may lead to a series of shut downs. Examples include the US Northeast blackouts of 1965,1977,2003, Transmission companies determine the maximum reliable capacity of each line to ensure that spare capacity is available in the event of a failure in another part of the network. High-voltage overhead conductors are not covered by insulation, the conductor material is nearly always an aluminum alloy, made into several strands and possibly reinforced with steel strands. Copper was sometimes used for transmission, but aluminum is lighter, yields only marginally reduced performance. Overhead conductors are a commodity supplied by companies worldwide
19.
AC power
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Power in an electric circuit is the rate of flow of energy past a given point of the circuit. In alternating current circuits, energy storage such as inductors and capacitors may result in periodic reversals of the direction of energy flow. The portion of power that, averaged over a cycle of the AC waveform. The portion of power due to stored energy, which returns to the source in each cycle, is known as reactive power, in a simple alternating current circuit consisting of a source and a linear load, both the current and voltage are sinusoidal. If the load is resistive, the two quantities reverse their polarity at the same time. At every instant the product of voltage and current is positive or zero, in this case, only active power is transferred. If the load is purely reactive, then the voltage and current are 90 degrees out of phase, There is no net energy flow over each half cycle. In this case, only reactive power flows, There is no net transfer of energy to the load, however electrical power does flow along the wires and returns by flowing in reverse along the same wires. During its travels both from the source to the reactive load and back to the power source, this purely reactive power flow loses energy to the line resistance. Practical loads have resistance as well as inductance, and/or capacitance, Power engineers analyse the apparent power as being the magnitude of the vector sum of active and reactive power. Apparent power is the product of the rms values of voltage, conductors, transformers and generators must be sized to carry the total current, not just the current that does useful work. Another consequence is that adding the apparent power for two loads will not accurately give the power unless they have the same phase difference between current and voltage. Conventionally, capacitors are treated as if they generate reactive power, if a capacitor and an inductor are placed in parallel, then the currents flowing through the capacitor and the inductor tend to cancel rather than add. The result of this is that capacitive and inductive circuit elements tend to each other out. Current lagging voltage, current leading voltage and these are all denoted in the diagram to the right. In the diagram, P is the power, Q is the reactive power, S is the complex power. Reactive power does not do any work, so it is represented as the axis of the vector diagram. Active power does do work, so it is the real axis, the unit for all forms of power is the watt, but this unit is generally reserved for active power
20.
Volt
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The volt is the derived unit for electric potential, electric potential difference, and electromotive force. One volt is defined as the difference in potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points. It is also equal to the difference between two parallel, infinite planes spaced 1 meter apart that create an electric field of 1 newton per coulomb. Additionally, it is the difference between two points that will impart one joule of energy per coulomb of charge that passes through it. It can also be expressed as amperes times ohms, watts per ampere, or joules per coulomb, for the Josephson constant, KJ = 2e/h, the conventional value KJ-90 is used, K J-90 =0.4835979 GHz μ V. This standard is typically realized using an array of several thousand or tens of thousands of junctions. Empirically, several experiments have shown that the method is independent of device design, material, measurement setup, etc. in the water-flow analogy sometimes used to explain electric circuits by comparing them with water-filled pipes, voltage is likened to difference in water pressure. Current is proportional to the diameter of the pipe or the amount of water flowing at that pressure. A resistor would be a reduced diameter somewhere in the piping, the relationship between voltage and current is defined by Ohms Law. Ohms Law is analogous to the Hagen–Poiseuille equation, as both are linear models relating flux and potential in their respective systems, the voltage produced by each electrochemical cell in a battery is determined by the chemistry of that cell. Cells can be combined in series for multiples of that voltage, mechanical generators can usually be constructed to any voltage in a range of feasibility. High-voltage electric power lines,110 kV and up Lightning, Varies greatly. Volta had determined that the most effective pair of metals to produce electricity was zinc. In 1861, Latimer Clark and Sir Charles Bright coined the name volt for the unit of resistance, by 1873, the British Association for the Advancement of Science had defined the volt, ohm, and farad. In 1881, the International Electrical Congress, now the International Electrotechnical Commission and they made the volt equal to 108 cgs units of voltage, the cgs system at the time being the customary system of units in science. At that time, the volt was defined as the difference across a conductor when a current of one ampere dissipates one watt of power. The international volt was defined in 1893 as 1/1.434 of the emf of a Clark cell and this definition was abandoned in 1908 in favor of a definition based on the international ohm and international ampere until the entire set of reproducible units was abandoned in 1948. Prior to the development of the Josephson junction voltage standard, the volt was maintained in laboratories using specially constructed batteries called standard cells
21.
Ferranti effect
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In electrical engineering, the Ferranti effect is an increase in voltage occurring at the receiving end of a long transmission line, above the voltage at the sending end. This occurs when the line is energized, but there is a light load or the load is disconnected. The capacitive line charging current produces a voltage drop across the inductance that is in-phase with the sending-end voltage. Therefore both line inductance and capacitance are responsible for this phenomenon, the Ferranti Effect will be more pronounced the longer the line and the higher the voltage applied. The relative voltage rise is proportional to the square of the line length, the Ferranti effect is much more pronounced in underground cables, even in short lengths, because of their high capacitance. It was first observed during the installation of cables in Sebastian Ziani de Ferrantis 10,000 volt distribution system in 1887
22.
Undergrounding
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Undergrounding is the replacement of overhead cables providing electrical power or telecommunications, with underground cables. Undergrounding can increase the costs of electric power transmission and distribution. Telegraph cable undergrounding was considered in Northern Germany as early as 1870, the aerial cables that carry high-voltage electricity and are supported by large pylons are generally considered an unattractive feature of the countryside. Underground cables can transmit power across densely populated or areas where land is costly or environmentally or aesthetically sensitive, underground and underwater crossings may be a practical alternative for crossing rivers. Less subject to damage from weather conditions Reduced range of electromagnetic fields emission. However depending on the depth of the cable, greater emf may be experienced. Underground cables pose no hazard to low flying aircraft or to wildlife, much less subject to conductor theft, illegal connections, sabotage, and damage from armed conflict. Above ground lines cost around $10 per foot and underground lines cost in the range of $20 to $40 per foot, in highly urbanized areas the cost of underground transmission can be 10-14 times as expensive as overhead. Whereas finding and repairing overhead wire breaks can be accomplished in hours, underground repairs can take days or weeks, underground cable locations are not always obvious, which can lead to unwary diggers damaging cables or being electrocuted. Operations are more difficult since the reactive power of underground cables produces large charging currents. Transmission and distribution companies generally future-proof underground lines by installing the cables while being still cost-effective. Underground cables are subject to damage by ground movement. The advantages can in some cases outweigh the disadvantages of the investment cost. Most electrical power in Japan is still provided by aerial cables, in Tokyos 23 wards, according to Japans Construction and Transport Ministry, just 7.3 percent of cables were laid underground as of March 2005. The UK regulator Office of Gas and Electricity Markets permits transmission companies to recoup the cost of some undergrounding in their prices to consumers, the undergrounding must be in National Parks or designated Areas of Outstanding Natural Beauty to qualify. The most visually intrusive overhead cables of the transmission network are excluded from the scheme. Some undergrounding projects are funded by the proceeds of the national lottery, all low and medium voltage electrical power in the Netherlands is now supplied underground. Other EU countries such as the UK and Germany are undergrounding a portion of their cables each year, in the United States, the California Public Utilities Commission Rule 20 permits the undergrounding of electrical power cables under certain situations
23.
Ethernet
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Ethernet /ˈiːθərnɛt/ is a family of computer networking technologies commonly used in local area networks, metropolitan area networks and wide area networks. It was commercially introduced in 1980 and first standardized in 1983 as IEEE802.3, over time, Ethernet has largely replaced competing wired LAN technologies such as token ring, FDDI and ARCNET. The original 10BASE5 Ethernet uses coaxial cable as a medium, while the newer Ethernet variants use twisted pair. Over the course of its history, Ethernet data transfer rates have increased from the original 2.94 megabits per second to the latest 100 gigabits per second. The Ethernet standards comprise several wiring and signaling variants of the OSI physical layer in use with Ethernet, systems communicating over Ethernet divide a stream of data into shorter pieces called frames. As per the OSI model, Ethernet provides services up to, since its commercial release, Ethernet has retained a good degree of backward compatibility. Features such as the 48-bit MAC address and Ethernet frame format have influenced other networking protocols, the primary alternative for some uses of contemporary LANs is Wi-Fi, a wireless protocol standardized as IEEE802.11. Ethernet was developed at Xerox PARC between 1973 and 1974 and it was inspired by ALOHAnet, which Robert Metcalfe had studied as part of his PhD dissertation. In 1975, Xerox filed a patent application listing Metcalfe, David Boggs, Chuck Thacker, in 1976, after the system was deployed at PARC, Metcalfe and Boggs published a seminal paper. Metcalfe left Xerox in June 1979 to form 3Com and he convinced Digital Equipment Corporation, Intel, and Xerox to work together to promote Ethernet as a standard. The so-called DIX standard, for Digital/Intel/Xerox, specified 10 Mbit/s Ethernet, with 48-bit destination and source addresses and it was published on September 30,1980 as The Ethernet, A Local Area Network. Data Link Layer and Physical Layer Specifications, version 2 was published in November,1982 and defines what has become known as Ethernet II. Formal standardization efforts proceeded at the time and resulted in the publication of IEEE802.3 on June 23,1983. Ethernet initially competed with two largely proprietary systems, Token Ring and Token Bus, in the process, 3Com became a major company. 3Com shipped its first 10 Mbit/s Ethernet 3C100 NIC in March 1981, an Ethernet adapter card for the IBM PC was released in 1982, and, by 1985, 3Com had sold 100,000. Parallel port based Ethernet adapters were produced for a time, with drivers for DOS, by the early 1990s, Ethernet became so prevalent that it was a must-have feature for modern computers, and Ethernet ports began to appear on some PCs and most workstations. This process was sped up with the introduction of 10BASE-T and its relatively small modular connector. Since then, Ethernet technology has evolved to meet new bandwidth, in addition to computers, Ethernet is now used to interconnect appliances and other personal devices
24.
Category 5 cable
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Category 5 cable, commonly referred to as Cat 5, is a twisted pair cable for carrying signals. This type of cable is used in structured cabling for computer networks such as Ethernet, the cable standard provides performance of up to 100 MHz and is suitable for 10BASE-T, 100BASE-TX, 1000BASE-T, and 2. 5GBASE-T. Cat 5 is also used to other signals such as telephony. This cable is connected using punch-down blocks and modular connectors. Most Category 5 cables are unshielded, relying on the balanced twisted pair design. Category 5 was superseded by the Category 5e specification, and later category 6 cable, the specification for category 5 cable was defined in ANSI/TIA/EIA-568-A, with clarification in TSB-95. These documents specify performance characteristics and test requirements for frequencies up to 100 MHz, cable types, connector types and cabling topologies are defined by TIA/EIA-568-B. Nearly always, 8P8C modular connectors are used for connecting category 5 cable, the cable is terminated in either the T568A scheme or the T568B scheme. The two schemes work equally well and may be mixed in an installation so long as the scheme is used on both ends of each cable. Each of the four pairs in a Cat 5 cable has differing precise number of twists per meter to minimize crosstalk between the pairs, although cable assemblies containing 4 pairs are common, category 5 is not limited to 4 pairs. Backbone applications involve using up to 100 pairs and this use of balanced lines helps preserve a high signal-to-noise ratio despite interference from both external sources and crosstalk from other pairs. The cable is available in both stranded and solid conductor forms, the stranded form is more flexible and withstands more bending without breaking. Permanent wiring is solid-core, while patch cables are stranded, the specific category of cable in use can be identified by the printing on the side of the cable. Most Category 5 cables can be bent at any radius exceeding approximately four times the diameter of the cable. The maximum length for a segment is 100 m per TIA/EIA 568-5-A. If longer runs are required, the use of hardware such as a repeater or switch is necessary. The specifications for 10BASE-T networking specify a 100-meter length between active devices and this allows for 90 meters of solid-core permanent wiring, two connectors and two stranded patch cables of 5 meters, one at each end. The category 5e specification improves upon the category 5 specification by revising and introducing new specifications to further mitigate the amount of crosstalk
25.
USB
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It is currently developed by the USB Implementers Forum. USB was designed to standardize the connection of peripherals to personal computers. It has become commonplace on other devices, such as smartphones, PDAs, USB has effectively replaced a variety of earlier interfaces, such as serial ports and parallel ports, as well as separate power chargers for portable devices. Also, there are 5 modes of USB data transfer, in order of increasing bandwidth, Low Speed, Full Speed, High Speed, SuperSpeed, USB devices have some choice of implemented modes, and USB version is not a reliable statement of implemented modes. Modes are identified by their names and icons, and the specifications suggests that plugs, unlike other data buses, USB connections are directed, with both upstream and downstream ports emanating from a single host. This applies to power, with only downstream facing ports providing power. Thus, USB cables have different ends, A and B, therefore, in general, each different format requires four different connectors, a plug and receptacle for each of the A and B ends. USB cables have the plugs, and the corresponding receptacles are on the computers or electronic devices, in common practice, the A end is usually the standard format, and the B side varies over standard, mini, and micro. The mini and micro formats also provide for USB On-The-Go with a hermaphroditic AB receptacle, the micro format is the most durable from the point of view of designed insertion lifetime. The standard and mini connectors have a lifetime of 1,500 insertion-removal cycles. Likewise, the component of the retention mechanism, parts that provide required gripping force, were also moved into plugs on the cable side. A group of seven companies began the development of USB in 1994, Compaq, DEC, IBM, Intel, Microsoft, NEC, a team including Ajay Bhatt worked on the standard at Intel, the first integrated circuits supporting USB were produced by Intel in 1995. The original USB1.0 specification, which was introduced in January 1996, Microsoft Windows 95, OSR2.1 provided OEM support for the devices. The first widely used version of USB was 1.1, the 12 Mbit/s data rate was intended for higher-speed devices such as disk drives, and the lower 1.5 Mbit/s rate for low data rate devices such as joysticks. Apple Inc. s iMac was the first mainstream product with USB, following Apples design decision to remove all legacy ports from the iMac, many PC manufacturers began building legacy-free PCs, which led to the broader PC market using USB as a standard. The USB2.0 specification was released in April 2000 and was ratified by the USB Implementers Forum at the end of 2001.1 specification, the USB3.0 specification was published on 12 November 2008. Its main goals were to increase the transfer rate, decrease power consumption, increase power output. USB3.0 includes a new, higher speed bus called SuperSpeed in parallel with the USB2.0 bus, for this reason, the new version is also called SuperSpeed
26.
HDMI
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HDMI is a digital replacement for analog video standards. HDMI implements the EIA/CEA-861 standards, which video formats and waveforms, transport of compressed, uncompressed, and LPCM audio, auxiliary data. CEA-861 signals carried by HDMI are electrically compatible with the CEA-861 signals used by the visual interface. No signal conversion is necessary, nor is there a loss of quality when a DVI-to-HDMI adapter is used. The CEC capability allows HDMI devices to each other when necessary. Several versions of HDMI have been developed and deployed since initial release of the technology but all use the same cable and connector. Other than improved audio and video capacity, performance, resolution and color spaces, newer versions have optional advanced features such as 3D, Ethernet data connection, production of consumer HDMI products started in late 2003. In Europe either DVI-HDCP or HDMI is included in the HD ready in-store labeling specification for TV sets for HDTV, HDMI began to appear on consumer HDTV camcorders and digital still cameras in 2006. As of January 6,2015, over 4 billion HDMI devices have been sold, the HDMI founders are Hitachi, Panasonic, Philips, Silicon Image, Sony, Thomson, RCA and Toshiba. Digital Content Protection, LLC provides HDCP for HDMI, HDMI has the support of motion picture producers Fox, Universal, Warner Bros. and Disney, along with system operators DirecTV, EchoStar and CableLabs. The HDMI founders began development on HDMI1.0 on April 16,2002, at the time, DVI-HDCP and DVI-HDTV were being used on HDTVs. HDMI1.0 was designed to improve on DVI-HDTV by using a connector and adding audio capability and enhanced YCbCr capability. The first Authorized Testing Center, which tests HDMI products, was opened by Silicon Image on June 23,2003, in California, the first ATC in Japan was opened by Panasonic on May 1,2004, in Osaka. The first ATC in Europe was opened by Philips on May 25,2005, in Caen, the first ATC in China was opened by Silicon Image on November 21,2005, in Shenzhen. The first ATC in India was opened by Philips on June 12,2008, the HDMI website contains a list of all the ATCs. According to In-Stat, the number of HDMI devices sold was 5 million in 2004,17.4 million in 2005,63 million in 2006, and 143 million in 2007. HDMI has become the de facto standard for HDTVs, and according to In-Stat, In-Stat has estimated that 229 million HDMI devices were sold in 2008. On April 8,2008 there were over 850 consumer electronics, on January 7,2009, HDMI Licensing, LLC announced that HDMI had reached an installed base of over 600 million HDMI devices
27.
IEEE 1394
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IEEE1394 is an interface standard for a serial bus for high-speed communications and isochronous real-time data transfer. It was developed in the late 1980s and early 1990s by Apple, the 1394 interface is also known by the brand i. LINK, and Lynx. The copper cable it uses in its most common implementation can be up to 4.5 metres long, power is also carried over this cable allowing devices with moderate power requirements to operate without a separate power supply. FireWire is also available in wireless, Cat 5, fiber optic, the 1394 interface is comparable to USB though USB requires a master controller and has greater market share. IEEE1394 replaced parallel SCSI in many applications, because of lower implementation costs, FireWire is Apples name for the IEEE1394 High Speed Serial Bus. IEEE1394 is a bus architecture for high-speed data transfer. FireWire is a bus, meaning that information is transferred one bit at a time. Parallel buses utilize a number of different physical connections, and as such are more costly and typically heavier. IEEE1394 fully supports both isochronous and asynchronous applications, Apple intended FireWire to be a serial replacement for the parallel SCSI bus while providing connectivity for digital audio and video equipment. Apples development began in the late 1980s, later presented to the IEEE, in 2007, IEEE1394 was a composite of four documents, the original IEEE Std. 1394-1995, the IEEE Std. 1394a-2000 amendment, the IEEE Std, 1394b-2002 amendment, and the IEEE Std. 1394c-2006 amendment. On June 12,2008, all these amendments as well as errata and some technical updates were incorporated into a superseding standard, Apple first included FireWire in some of its 1999 Macintosh models, and most Apple Macintosh computers manufactured in the years 2000 through 2011 included FireWire ports. However, in February 2011 Apple introduced the first commercially available computer with Thunderbolt, Apple released its last computers featuring FireWire late 2012. By 2014 Thunderbolt had become a feature across Apples entire line of computers effectively becoming the spiritual successor to FireWire in the Apple ecosystem. This style was added into the 1394a amendment. This port is sometimes labeled S100 or S400 to indicate speed in Mbit/s, the system was commonly used to connect data storage devices and DV cameras, but was also popular in industrial systems for machine vision and professional audio systems. Many users preferred it over the more common USB2.0 for its then greater effective speed, benchmarks show that the sustained data transfer rates are higher for FireWire than for USB2.0, but lower than USB3.0. Results are marked on Apple Mac OS X but more varied on Microsoft Windows, implementation of IEEE1394 is said to require use of 261 issued international patents held by 10 corporations
28.
Video Graphics Array
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Video Graphics Array is the display hardware first introduced with the IBM PS/2 line of computers in 1987. Today, the VGA analog interface is used for high definition video, including resolutions of 1080p, while the transmission bandwidth of VGA is high enough to support even higher resolution playback, there can be picture quality degradation depending on cable quality and length. How discernible this degradation is depends on the individuals eyesight and the display, though it is noticeable when switching to. The VGA supports both All Points Addressable graphics modes, and alphanumeric text modes, the other color modes defaulted to standard EGA or CGA compatible palettes, but could still be redefined if desired using VGA-specific programming. g. 400×600 or 360×480, and thin pixels,16 colors and the 70 Hz refresh rate with e. g. 736×410 mode. Its single-chip implementation allowed the VGA to be placed directly on a PC′s motherboard with a minimum of difficulty, since it only required video memory, timing crystals, the original VGA specifications are as follows,256 KB Video RAM 16-color and 256-color paletted display modes. 262, 144-color global palette Selectable 25.175 MHz or 28.322 MHz master pixel clock Usual line rate fixed at 31, compatibility is almost full at BIOS level, but even at register level, a very high value of compatibility is reached. The formula for the VGA horizontal frequency is thus ×525 kHz =4500 ÷143 kHz ≈31.4685 kHz, All other frequencies used by the VGA card are derived from this value by integer multiplication or division. Since the exactness of quartz oscillators is limited, real cards will have higher or lower frequency. All derived VGA timings can be varied widely by software that bypasses the VGA firmware interface and communicates directly with the VGA hardware, the use of other timings may in fact damage such monitors and thus was usually avoided by software publishers. For the most common VGA mode, the timings are. The figures shown in this image may be inaccurate and not match the above table exactly. The same general layout applies, merely at a lower frequency and these timings are the same in the higher frequency mode, but all pixel counts are correspondingly multiplied by 9/8ths – thus,720 active pixels,900 total per line, and a 54 pixel back porch. The monitor is triggered into synchronising at the higher frame rate by use of a positive-polarity VSync pulse. Depending on manufacturer, the details of active period and front/back porch widths, particularly in the horizontal domain. 640×400 @70 Hz is traditionally the video used for booting most VGA-compatible x86 personal computers which show a graphical boot screen. 640×480 @60 Hz is the default Windows graphics mode, up to Windows 2000 and it remains an option in XP and later versions via the boot menu low resolution video option and per-application compatibility mode settings. 320×200 @70 Hz is the most common mode for VGA-era PC games, using exactly the same timings as the 640×400 mode, the actual timings vary slightly from the defined standard
29.
DisplayPort
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DisplayPort is a digital display interface developed by the Video Electronics Standards Association. The interface is used to connect a video source to a display device such as a computer monitor, though it can also be used to carry audio, USB. VESA designed it to replace VGA, DVI, and FPD-Link, DisplayPort is backwards compatible with VGA, DVI and HDMI through the use of passive and active adapters. DisplayPort is the first display interface to rely on packetized data transmission, a form of communication found in technologies including Ethernet, USB. The use of data packets also allows DisplayPort to be extensible, DisplayPort can be used to transmit audio and video simultaneously, but each one is optional and can be transmitted without the other. A bi-directional, half-duplex auxiliary channel carries device management and device control data for the Main Link, such as VESA EDID, MCCS, in addition, the interface is capable of carrying bi-directional USB signals. The DisplayPort LVDS signal protocol is not compatible with DVI or HDMI, analog VGA and dual-link DVI require powered active adapters to convert the protocol and signal levels and do not rely on dual mode. VGA adapters are powered by the DisplayPort connector, while dual-link DVI adapters may rely on a power source. The first version,1.0, was approved by VESA on 3 May 2006, version 1. 1a was ratified on 2 April 2007. DisplayPort 1.0 allows a maximum of 8.64 Gbit/s data rate over a 2-meter cable and it also includes HDCP in addition to DisplayPort Content Protection. The DisplayPort 1. 1a specification can be downloaded for free from the VESA website, DisplayPort version 1.2 was approved on 22 December 2009. Also Apple Inc. s Mini DisplayPort connector, which is smaller and designed for laptop computers. DisplayPort version 1. 2a may optionally include VESAs Adaptive Sync, aMDs FreeSync utilizes the DisplayPort Adaptive-Sync feature for operation. 2a. As it is a feature, support for Adaptive-Sync is not required for a display to be DisplayPort 1. 2a-compliant. DisplayPort version 1.3 was approved on 15 September 2014 and this bandwidth is enough for a 4K UHD display at 120 Hz, a 5K display at 60 Hz, or an 8K UHD display at 30 Hz, with 24-bit RGB color. Using Multi-Stream Transport, it can support two 4K UHD displays at 60 Hz, or up to four WQXGA displays at 60 Hz in 24-bit RGB mode. The new standard includes mandatory Dual-mode support for DVI and HDMI adapters, with support for the HDMI2.0 standard and HDCP2.2 content protection. The Thunderbolt 3 connection standard was originally to support for DisplayPort 1.3
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Digital Visual Interface
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Digital Visual Interface is a video display interface developed by the Digital Display Working Group. The digital interface is used to connect a source, such as a video display controller, to a display device. It was developed with the intention of creating a standard for the transfer of digital video content. The interface is designed to transmit uncompressed digital video and can be configured to support multiple modes such as DVI-A, featuring support for analog connections, the DVI specification is compatible with the VGA interface. This compatibility, along with other advantages, led to its widespread acceptance over competing digital display standards Plug and Display, although DVI is predominantly associated with computers, it is sometimes used in other consumer electronics such as television sets and DVD players. DVIs digital video format is based on panelLink, a serial format developed by Silicon Image that utilizes a high-speed serial link called transition minimized differential signaling. Like modern analog VGA connectors, the DVI connector includes pins for the data channel. A newer version of DDC called DDC2 allows the graphics adapter to read the monitors extended display identification data, if a display supports both analog and digital signals in one DVI-I input, each input method can host a distinct EDID. Since the DDC can only support one EDID, there can be a problem if both the digital and analog inputs in the DVI-I port detect activity and it is up to the display to choose which EDID to send. When a source and display are connected, the source first queries the displays capabilities by reading the monitor EDID block over an I²C link, the EDID block contains the displays identification, color characteristics, and table of supported video modes. The table can designate a preferred mode or native resolution, for backward compatibility with displays using analog VGA signals, some of the contacts in the DVI connector carry the analog VGA signals. To ensure a level of interoperability, DVI compliant devices are required to support one baseline video mode. Digitally encoded video pixel data is transported using multiple TMDS links, at the electrical level, these links are highly resistant to electrical noise and other forms of analog distortion. A single link DVI connection consists of four TMDS links, each link transmits data from the source to the device over one twisted wire pair. Three of the links represent the RGB components – red, green, the fourth link carries the pixel clock. The binary data is encoded using 8b10b encoding, DVI does not use packetization, but rather transmits the pixel data as if it were a rasterized analog video signal. As such, the frame is drawn during each vertical refresh period. The full active area of each frame is transmitted without compression
31.
PCI Express
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PCI Express, officially abbreviated as PCIe or PCI-e, is a high-speed serial computer expansion bus standard, designed to replace the older PCI, PCI-X, and AGP bus standards. More recent revisions of the PCIe standard provide hardware support for I/O virtualization, format specifications are maintained and developed by the PCI-SIG, a group of more than 900 companies that also maintain the conventional PCI specifications. PCIe 3.0 is the latest standard for expansion cards that are in production, conceptually, the PCI Express bus is a high-speed serial replacement of the older PCI/PCI-X bus. In contrast, PCI Express is based on point-to-point topology, with separate serial links connecting every device to the root complex. Due to its bus topology, access to the older PCI bus is arbitrated. Furthermore, the older PCI clocking scheme limits the bus clock to the slowest peripheral on the bus, in contrast, a PCI Express bus link supports full-duplex communication between any two endpoints, with no inherent limitation on concurrent access across multiple endpoints. In terms of bus protocol, PCI Express communication is encapsulated in packets, the work of packetizing and de-packetizing data and status-message traffic is handled by the transaction layer of the PCI Express port. Radical differences in electrical signaling and bus protocol require the use of a different mechanical form factor and expansion connectors, PCI slots, the PCI Express link between two devices can consist of anywhere from one to 32 lanes. In a multi-lane link, the data is striped across lanes. The lane count is automatically negotiated during device initialization, and can be restricted by either endpoint, for example, a single-lane PCI Express card can be inserted into a multi-lane slot, and the initialization cycle auto-negotiates the highest mutually supported lane count. The link can dynamically down-configure itself to use fewer lanes, providing a failure tolerance in case bad or unreliable lanes are present, the PCI Express standard defines slots and connectors for multiple widths, ×1, ×4, ×8, ×12, ×16 and ×32. As a point of reference, a PCI-X device and a PCI Express 1.0 device using four lanes have roughly the same peak single-direction transfer rate of 1064 MB/s, PCI Express devices communicate via a logical connection called an interconnect or link. A link is a point-to-point communication channel between two PCI Express ports allowing both of them to send and receive ordinary PCI requests and interrupts, at the physical level, a link is composed of one or more lanes. Low-speed peripherals use a link, while a graphics adapter typically uses a much wider and faster 16-lane link. A lane is composed of two differential signaling pairs, with one pair for receiving data and the other for transmitting, thus, each lane is composed of four wires or signal traces. Conceptually, each lane is used as a byte stream. Physical PCI Express links may contain one to 32 lanes. Lane counts are written with an × prefix, with ×16 being the largest size in common use, despite being transmitted simultaneously as a single word, signals on a parallel interface have different travel duration and arrive at their destinations at different times
32.
Nominal impedance
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Nominal impedance in electrical engineering and audio engineering refers to the approximate designed impedance of an electrical circuit or device. The term is applied in a number of different fields, most often being encountered in respect of, The nominal value of the characteristic impedance of a cable or other form of transmission line. The nominal value of the input, output or image impedance of a port of a network, especially a network intended for use with a transmission line, such as filters, equalisers and amplifiers. The nominal value of the impedance of a radio frequency antenna The actual impedance may vary quite considerably from the nominal figure with changes in frequency. In the case of cables and other lines, there is also variation along the length of the cable. Depending on the field of application, nominal impedance is implicitly referring to a point on the frequency response of the circuit under consideration. This may be at low-frequency, mid-band or some other point, in most applications, there are a number of values of nominal impedance that are recognised as being standard. The nominal impedance of a component or circuit is often assigned one of these standard values, the item is assigned the nearest standard value. Nominal impedance first started to be specified in the days of telecommunications. At first amplifiers were not available and when they did become available they were expensive and it was consequently necessary to achieve maximum power transfer from the cable at the receiving end in order to maximise the lengths of cables that could be installed. It also became apparent that reflections on the line would severely limit the bandwidth that could be used or the distance that it was practicable to transmit. Matching equipment impedance to the impedance of the cable reduces reflections. To this end, all cables and equipment started to be specified to a nominal impedance. The earliest, and still the most widespread, standard is 600 Ω and it has to be said that the choice of this figure had more to do with the way telephones were interfaced into the local exchange than any characteristic of the local telephone cable. Telephones connect to the exchange through twisted pair cabling, each leg of the pair is connected to a relay coil which detect the signalling on the line. The other end of one coil is connected to a supply voltage, a telephone exchange relay coil is around 300 Ω so the two of them together are terminating the line in 600 Ω. The wiring to the subscriber in telephone networks is generally done in twisted pair cable and its impedance at audio frequencies, and especially at the more restricted telephone band frequencies, is far from constant. It is possible to manufacture this kind of cable to have a 600 Ω characteristic impedance and this might be quoted as a nominal 600 Ω impedance at 800 Hz or 1 kHz
33.
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
34.
Microwave
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Microwaves are a form of electromagnetic radiation with wavelengths ranging from one meter to one millimeter, with frequencies between 300 MHz and 300 GHz. Different sources define different frequency ranges as microwaves, the broad definition includes both UHF and EHF bands. A more common definition in radio engineering is the range between 1 and 100 GHz, in all cases, microwaves include the entire SHF band at minimum. Frequencies in the range are often referred to by their IEEE radar band designations, S, C, X, Ku, K, or Ka band. The prefix micro- in microwave is not meant to suggest a wavelength in the micrometer range and it indicates that microwaves are small, compared to waves used in typical radio broadcasting, in that they have shorter wavelengths. The boundaries between far infrared, terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study. At the high end of the band they are absorbed by gases in the atmosphere, microwaves are extremely widely used in modern technology. Although at the low end of the band they can pass through building walls enough for useful reception, therefore on the surface of the Earth microwave communication links are limited by the visual horizon to about 30 -40 miles. Microwaves are absorbed by moisture in the atmosphere, and the attenuation increases with frequency, beginning at about 40 GHz, atmospheric gases also begin to absorb microwaves, so above this frequency microwave transmission is limited to a few kilometers. A spectral band structure causes absorption peaks at specific frequencies, in a microwave beam directed at an angle into the sky, a small amount of the power will be randomly scattered as the beam passes through the troposphere. A sensitive receiver beyond the horizon with a high gain antenna focused on that area of the troposphere can pick up the signal. This technique has been used at frequencies between 0.45 and 5 GHz in tropospheric scatter communication systems to communicate beyond the horizon and their short wavelength allows narrow beams of microwaves to be produced by conveniently small high gain antennas from a half meter to 5 meters in diameter. Therefore beams of microwaves are used for point-to-point communication links, an advantage of narrow beams is that they allow frequency reuse by nearby transmitters. Parabolic antennas are the most widely used directive antennas at microwave frequencies, flat microstrip antennas are being increasingly used in consumer devices. Where omnidirectional antennas are required, for example in wireless devices and Wifi routers for wireless LANs, small monopoles, dipole, or patch antennas are used. Due to the high cost and maintenance requirements of waveguide runs, the term microwave also has a more technical meaning in electromagnetics and circuit theory. As a consequence, practical microwave circuits tend to away from the discrete resistors, capacitors. Open-wire and coaxial transmission lines used at lower frequencies are replaced by waveguides and stripline, high-power microwave sources use specialized vacuum tubes to generate microwaves
35.
Video
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Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video systems vary greatly in the resolution of the display and refresh rate, video can be carried on a variety of media, including radio broadcast, tapes, DVDs, computer files etc. Video was originally exclusively a live technology, charles Ginsburg led an Ampex research team developing one of the first practical video tape recorder. In 1951 the first video tape recorder captured live images from television cameras by converting the electrical impulses. Video recorders were sold for $50,000 in 1956, however, prices gradually dropped over the years, in 1971, Sony began selling videocassette recorder decks and tapes into the consumer market. The use of techniques in video created digital video, which allowed higher quality and, eventually. After the invention of the DVD in 1997 and Blu-ray Disc in 2006, sales of videotape, the advent of digital broadcasting and the subsequent digital television transition is in the process of relegating analog video to the status of a legacy technology in most parts of the world. PAL standards and SECAM specify 25 frame/s, while NTSC standards specify 29.97 frames, film is shot at the slower frame rate of 24 frames per second, which slightly complicates the process of transferring a cinematic motion picture to video. The minimum frame rate to achieve a comfortable illusion of an image is about sixteen frames per second. Video can be interlaced or progressive, analog display devices reproduce each frame in the same way, effectively doubling the frame rate as far as perceptible overall flicker is concerned. NTSC, PAL and SECAM are interlaced formats, abbreviated video resolution specifications often include an i to indicate interlacing. For example, PAL video format is specified as 576i50, where 576 indicates the total number of horizontal scan lines, i indicates interlacing. In progressive scan systems, each refresh period updates all scan lines in each frame in sequence, when displaying a natively progressive broadcast or recorded signal, the result is optimum spatial resolution of both the stationary and moving parts of the image. Deinterlacing cannot, however, produce video quality that is equivalent to true progressive scan source material, aspect ratio describes the dimensions of video screens and video picture elements. All popular video formats are rectilinear, and so can be described by a ratio between width and height, the screen aspect ratio of a traditional television screen is 4,3, or about 1.33,1. High definition televisions use a ratio of 16,9. The aspect ratio of a full 35 mm film frame with soundtrack is 1.375,1. Therefore, a 720 by 480 pixel NTSC DV image displayes with the 4,3 aspect ratio if the pixels are thin, the popularity of viewing video on mobile phones has led to the growth of vertical video
36.
Maxwell's equations
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Maxwells equations are a set of partial differential equations that, together with the Lorentz force law, form the foundation of classical electromagnetism, classical optics, and electric circuits. They underpin all electric, optical and radio such as power generation, electric motors, wireless communication, cameras, televisions. Maxwells equations describe how electric and magnetic fields are generated by charges, currents, one important consequence of the equations is the demonstration of how fluctuating electric and magnetic fields can propagate at the speed of light. This electromagnetic radiation manifests itself in ways from radio waves to light. The equations have two major variants, the microscopic Maxwell equations have universal applicability but are unwieldy for common calculations. They relate the electric and magnetic fields to total charge and total current, including the complicated charges, the macroscopic Maxwell equations define two new auxiliary fields that describe the large-scale behaviour of matter without having to consider atomic scale details. However, their use requires experimentally determining parameters for a description of the electromagnetic response of materials. The term Maxwells equations is used for equivalent alternative formulations. The space-time formulations, are used in high energy and gravitational physics because they make the compatibility of the equations with special and general relativity manifest. In many situations, though, deviations from Maxwells equations are immeasurably small, exceptions include nonclassical light, photon-photon scattering, quantum optics, and many other phenomena related to photons or virtual photons. In the electric and magnetic field there are four equations. The two inhomogeneous equations describe how the fields vary in space due to sources, Gausss law describes how electric fields emanate from electric charges. Gausss law for magnetism describes magnetic fields as closed field lines not due to magnetic monopoles, the two homogeneous equations describe how the fields circulate around their respective sources. A separate law of nature, the Lorentz force law, describes how the electric and magnetic field act on charged particles, a version of this law was included in the original equations by Maxwell but, by convention, is no longer. The precise formulation of Maxwells equations depends on the definition of the quantities involved. Conventions differ with the systems, because various definitions and dimensions are changed by absorbing dimensionful factors like the speed of light c. This makes constants come out differently, the vector calculus formulation below has become standard. For formulations using tensor calculus or differential forms, see alternative formulations, for relativistically invariant formulations, see relativistic formulations
37.
Space cloth
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Space cloth is a hypothetical infinite plane of conductive material having a resistance of η ohms per square, where η is the Impedance of free space. For example, a pad surrounded by a ring on a printed circuit board is similar to the cross section of a coaxial cable transmission line. The figure to the shows a coaxial cable terminated by space cloth. In the case of a structure like a coaxial cable. The computation of resistance between the conductors can be computed with 2D electromagnetic field solver methods including the relaxation method, in the case of a coaxial cable, there is a closed form solution. The resistive surface is considered to be a series of infinitesimal annular rings, each having a width of dρ, the resistance between the inner electrode and the outer electrode is just the integral over all such rings. R = ∫ r 1 r 2 η2 π ρ d ρ = η2 π ln r 2 r 1 This is exactly the equation for the impedance of a coaxial cable in free space. The structure has two transmission eigen-modes which are the mode and the common mode. In general, the eigen-modes have different characteristic impedances, if w >> h1, h2 >> t, then the field in region IV and V and can be ignored. The common mode characteristic impedance is the resistance of region II in parallel with region III. Z C M = R I I2 = η h 22 w In the differential mode, Z D M = R I +2 R I I = η w 2 h 2 h 1 h 1 +2 h 2
38.
International Standard Book Number
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The International Standard Book Number is a unique numeric commercial book identifier. An ISBN is assigned to each edition and variation of a book, for example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, the method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country. The initial ISBN configuration of recognition was generated in 1967 based upon the 9-digit Standard Book Numbering created in 1966, the 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108. Occasionally, a book may appear without a printed ISBN if it is printed privately or the author does not follow the usual ISBN procedure, however, this can be rectified later. Another identifier, the International Standard Serial Number, identifies periodical publications such as magazines, the ISBN configuration of recognition was generated in 1967 in the United Kingdom by David Whitaker and in 1968 in the US by Emery Koltay. The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108, the United Kingdom continued to use the 9-digit SBN code until 1974. The ISO on-line facility only refers back to 1978, an SBN may be converted to an ISBN by prefixing the digit 0. For example, the edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has SBN340013818 -340 indicating the publisher,01381 their serial number. This can be converted to ISBN 0-340-01381-8, the check digit does not need to be re-calculated, since 1 January 2007, ISBNs have contained 13 digits, a format that is compatible with Bookland European Article Number EAN-13s. An ISBN is assigned to each edition and variation of a book, for example, an ebook, a paperback, and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, a 13-digit ISBN can be separated into its parts, and when this is done it is customary to separate the parts with hyphens or spaces. Separating the parts of a 10-digit ISBN is also done with either hyphens or spaces, figuring out how to correctly separate a given ISBN number is complicated, because most of the parts do not use a fixed number of digits. ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency that is responsible for country or territory regardless of the publication language. Some ISBN registration agencies are based in national libraries or within ministries of culture, in other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded. In Canada, ISBNs are issued at no cost with the purpose of encouraging Canadian culture. In the United Kingdom, United States, and some countries, where the service is provided by non-government-funded organisations. Australia, ISBNs are issued by the library services agency Thorpe-Bowker
39.
General Services Administration
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The General Services Administration is an independent agency of the United States government, established in 1949 to help manage and support the basic functioning of federal agencies. GSA employs about 12,000 federal workers and has an operating budget of roughly $26.3 billion. GSA oversees $66 billion of procurement annually and it contributes to the management of about $500 billion in U. S. federal property, divided chiefly among 8,300 owned and leased buildings and a 210,000 vehicle motor pool. GSAs business lines include the Federal Acquisition Service, the Public Buildings Service, the GSA is member of the Procurement G6, an informal group leading the use of framework agreements and e-procurement instruments in public procurement. In 1947 President Harry Truman asked former President Herbert Hoover to lead what became known as the Hoover Commission to make recommendations to reorganize the operations of the federal government, one of the recommendations of the commission was the establishment of an Office of the General Services. This proposed office would combine the responsibilities of the following organizations, General Jess Larson, Administrator of the War Assets Administration, was named GSAs first Administrator. The first job awaiting Administrator Larson and the newly formed GSA was a renovation of the White House. The structure had fallen into such a state of disrepair by 1949 that one inspector of the time said the structure was standing “purely from habit. Everything, except the four walls without a roof, was stripped down. GSA completed the renovation in 1952, GSA headquarters, located at Eighteenth and F Streets, NW, was U. S. General Services Administration Building listed on the National Register of Historic Places in 1986 as Interior Department Offices, in 1960, GSA created the Federal Telecommunications System, a government-wide intercity telephone system. In 1970, the Nixon administration created the Consumer Product Information Coordinating Center, the Federal Buildings Fund was initiated in 1974, which allowed the GSA to issue rent bills to federal agencies. In 1972, the GSA established the Automated Data and Telecommunications Service, in 1973, the GSA created the Office of Federal Management Policy. GSA’s Office of Acquisition Policy centralized procurement policy in 1978, in 1984, GSA introduced the federal government to the use of charge cards, known as the GMA SmartPay system. The National Archives and Records Administration was spun off into an independent agency in 1985, the same year, the GSA began to provide governmentwide policy oversight and guidance for federal real property management as a result of an Executive Order signed by President Ronald Reagan. In 2003, the Federal Protective Service was moved to the Department of Homeland Security, in 2005, GSA reorganized to merge the Federal Supply Service and Federal Technology Service business lines into the Federal Acquisition Service. On April 3,2009, President Barack Obama nominated Martha N. Johnson to serve as the GSA Administrator, after a 9-month delay, the United States Senate confirmed her nomination on February 4,2010. In July 1991, GSA contractors began the excavation of what is now the Ted Weiss Federal Building in New York City, when initial excavation disturbed burials, destroying skeletons and artifacts, GSA sent archaeologists to excavate—but hid their findings from the public
40.
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
41.
History of telecommunication
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The history of telecommunication began with the use of smoke signals and drums in Africa, the Americas and parts of Asia. In the 1790s, the first fixed semaphore systems emerged in Europe and this article details the history of telecommunication and the individuals who helped make telecommunication systems what they are today. The history of telecommunication is an important part of the history of communication. Early telecommunications included smoke signals and drums, talking drums were used by natives in Africa, New Guinea and South America, and smoke signals in North America and China. Contrary to what one might think, these systems were used to do more than merely announce the presence of a military camp. In Rabbinical Judaism a signal was given by means of kerchiefs or flags at intervals along the way back to the high priest to indicate the goat for Azazel had been pushed from the cliff, greek hydraulic semaphore systems were used as early as the 4th century BC. The hydraulic semaphores, which worked with water filled vessels and visual signals, however, they could only utilize a very limited range of pre-determined messages, and as with all such optical telegraphs could only be deployed during good visibility conditions. During the Middle Ages, chains of beacons were 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, french engineer Claude Chappe began working on visual telegraphy in 1790, using pairs of clocks whose hands pointed at different symbols. These did not prove quite viable at long distances, and Chappe revised his model to use two sets of jointed wooden beams, operators moved the beams using cranks and wires. He built his first telegraph line between Lille and Paris, followed by a line from Strasbourg to Paris, in 1794, a Swedish engineer, Abraham Edelcrantz built a quite different system from Stockholm to Drottningholm. As opposed to Chappes system which involved pulleys rotating beams of wood, however semaphore as a communication system suffered from the need for skilled operators and expensive towers often at intervals of only ten to thirty kilometres. As a result, the last commercial line was abandoned in 1880, experiments on communication with electricity, initially unsuccessful, started in about 1726. Scientists including Laplace, Ampère, and Gauss were involved, both their designs employed multiple wires in order to visually represent almost all Latin letters and numerals. Thus, messages could be conveyed electrically up to a few kilometers, the telegraph receivers operator would visually observe the bubbles and could then record the transmitted message, albeit at a very low baud rate. The first working telegraph was built by Francis Ronalds in 1816, Charles Wheatstone and William Fothergill Cooke patented a five-needle, six-wire system, which entered commercial use in 1838. It used the deflection of needles to represent messages and started operating over twenty-one kilometres of the Great Western Railway on 9 April 1839, both Wheatstone and Cooke viewed their device as an improvement to the electromagnetic telegraph not as a new device
This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C".
