The hybrid system (tube pre-amps, solid-state power amps) can drive headphones of four different impedances: 275, 21960, 275, and 120 ohms.
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The hybrid system (tube pre-amps, solid-state power amps) can drive headphones of four different impedances: 0.1, 33, 19603, and 120 ohms.
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For the most part, audio systems both professional and domestic, have their components interconnected with low impedance outputs connected to high impedance inputs. These impedances are poorly defined and nominal impedances are not usually assigned for this kind of connection. The exact impedances make little difference to performance as long as the latter is many times larger than the former.Eargle & Foreman, p.83.
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The behaviour of sound waves encountering a different medium is dictated by the differing acoustic impedances. As with electrical impedances, there are matches and mismatches and energy will be transferred for certain frequencies (up to nearly 100%) whereas for others it could be mostly reflected (again, up to very large percentages). In amplifier and loudspeaker design electrical impedances, mechanical impedances, and acoustic impedances of the system have to be balanced such that the frequency and phase response least alter the reproduced sound across a very broad spectrum whilst still producing adequate sound levels for the listener. Modelling acoustical systems using the same (or similar) techniques long used in electrical circuits gave acoustical designers a new and powerful design tool.
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The equations given here are valid for complex as well as real impedances.
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400px A network of impedances with more than two terminals cannot be reduced to a single impedance equivalent circuit. An n-terminal network can, at best, be reduced to n impedances (at worst nC2). For a three terminal network, the three impedances can be expressed as a three node delta (Δ) network or four node star (Y) network. These two networks are equivalent and the transformations between them are given below.
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The voltage around a loop must sum up to zero, so the voltage drops must be divided evenly in a direct relationship with the impedance. To be specific, if two or more impedances are in parallel, the current that enters the combination will be split between them in inverse proportion to their impedances (according to Ohm's law). It also follows that if the impedances have the same value the current is split equally.
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The equations below are expressed as resistances but apply equally to the general case with impedances.
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It is necessary for antimetry that the terminating impedances are also the dual of each other, but in many practical cases the two terminating impedances are resistors and are both equal to the nominal impedance R0. Hence, they are both symmetric and antimetric at the same time.
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The image analysis starts with a calculation of the input and output impedances (the image impedances) and the transfer function of a section in an infinite chain of identical sections. This can be shown to be equivalent to the performance of a section terminated in its image impedances.Lee, p.825, Laplante, p.341.
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The difficulty that he was trying to overcome was that the image impedance techniques being used to design filter sections only gave the mathematically predicted response if they were terminated in their respective image impedances. Technically, this was easy to do within the filter as it could always be arranged that adjacent filter sections had matching image impedances (one of the characteristics of m-type sections is that one side or the other of the m-type section will have an image impedance identical to the equivalent constant k section). However, the terminating impedances are a different story.
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The symmetrical network is bisected along its plane of symmetry. One half is impedance-scaled to the input impedance and the other is scaled to the output impedance. The response shape of the filter remains the same. This does not amount to an impedance matching network, the impedances looking in to the network ports bear no relationship to the termination impedances.
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Speaker L pads are designed to match the impedance of the speaker, so they were commonly available with 4, 8, and 16 Ω impedances.
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The combination is a wideband transmission line with considerable delay per unit length. Both ends of the delay cable require matched impedances to avoid reflections.
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A low pass ladder filter and an implementation using frequency dependent negative resistors (FDNR). Ra and Rb are added for practical reasons. If all the impedances (including the source and load impedances) of a passive ladder filter are divided by sk, the transfer function is not changed. The effect of this division is to transform resistors into capacitors, inductors into resistors and capacitors into FDNRs.
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The nodes of the signal-flow graph will include both voltages and currents. The branch gains will include impedances and admittances. :4. Convert all nodes of the signal-flow graph to voltages and all impedances to dimensionless transmittances. This is accomplished by dividing all impedance elements by R, an arbitrary resistance and multiplying all admittance elements by R. This scaling does not change the frequency response. :5.
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A matched amplifier, in this case, refers to a condition in which the input and output impedances are conjugately matched to the source and load, respectively.
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The Laplace transform is often used in circuit analysis, and simple conversions to the -domain of circuit elements can be made. Circuit elements can be transformed into impedances, very similar to phasor impedances. Here is a summary of equivalents: : -domain equivalent circuits Note that the resistor is exactly the same in the time domain and the -domain. The sources are put in if there are initial conditions on the circuit elements.
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Julius Futterman pioneered a type of amplifier known as "output transformerless" (OTL). These use paralleled valves to match with speaker impedances (typically 8 ohms). This design require numerous valves, run hot, and because they attempt to match impedances in a way fundamentally different from a transformer, they often have a unique sound quality. 6080 triodes, designed for regulated power supplies, were low- impedance types sometimes pressed into transformerless use.
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Such circuits can be converted to all shunt components in the same step used to space the components with the first two identities. The third and fourth identities allow characteristic impedances to be scaled down or up respectively. These can be useful for transforming impedances that are impractical to implement. However, they have the disadvantage of requiring the addition of an ideal transformer with a turns ratio equal to the scaling factor.
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This is called the nominal impedance. Amplifiers can therefore be safely specified to operate into a load that has this nominal impedance (or higher, but not lower). Typical nominal impedances for speakers include 4, 6, 8 and 16Ω (ohms), with 4Ω being most common in in- car loudspeakers, and 8Ω being most common elsewhere. A loudspeaker with an 8Ω nominal impedance may exhibit actual impedances ranging from approximately 5 to 100Ω depending on frequency.
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The widespread idea that 50 Ω and 75 Ω cable nominal impedances arose in connection with the input impedance of various antennae is a myth. It is true, however, that several common antennae are easily matched to cables with these nominal impedances. A quarter wavelength monopole in free space has an impedance of 36.5 Ω,Chen, pp.574–575. and a half wavelength dipole in free space has an impedance of 72 Ω.Gulati, p.424.
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A system one- line diagram is the basis to build a mathematical model of the generators, loads, buses, and transmission lines of the system, and their electrical impedances and ratings.
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A general network with an arbitrary number of nodes cannot be reduced to the minimum number of impedances using only series and parallel combinations. In general, Y-Δ and Δ-Y transformations must also be used. For some networks the extension of Y-Δ to star-polygon transformations may also be required. For equivalence, the impedances between any pair of terminals must be the same for both networks, resulting in a set of three simultaneous equations.
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One simply needs to know the input impedance Rp and to choose the output impedance Rs. Or conversely know Rs and choose Rp. Keep in mind that Rp must be larger than Rs. Because reactance is frequency dependent the L network will only transform the impedances at one frequency. Inclusion of two L networks back to back creates what is known as a T-network. T-networks work well for matching an even greater range of impedances.
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The input impedance of the differential pair highly depends on the input mode. At common mode, the two parts behave as common-collector stages with high emitter loads; so, the input impedances are extremely high. At differential mode, they behave as common-emitter stages with grounded emitters; so, the input impedances are low. The output impedance of the differential pair is high (especially for the improved differential pair with a current mirror as shown in Figure 3).
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Power amplifier by Skyworks Solutions in a Smartphone. A power amplifier is an amplifier designed primarily to increase the power available to a load. In practice, amplifier power gain depends on the source and load impedances, as well as the inherent voltage and current gain. A radio frequency (RF) amplifier design typically optimizes impedances for power transfer, while audio and instrumentation amplifier designs normally optimize input and output impedance for least loading and highest signal integrity.
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Simple 'L' network with series impedance Z and shunt admittance Y. Image impedances Zi 1 and Zi 2 are shown Showing how a T section is made from two cascaded L half sections. Zi 2 is facing Zi 2 to provide matching impedances Showing how a Π section is made from two cascaded L half sections. Zi 1 is facing Zi 1 to provide matching impedances As an example, the derivation of the image impedances of a simple 'L' network is given below. The L network consists of a series impedance, Z, and a shunt admittance, Y. The difficulty here is that in order to find Zi 1 it is first necessary to terminate port 2 with Zi 2. However, Zi 2 is also an unknown at this stage. The problem is solved by terminating port 2 with an identical network: port 2 of the second network is connected to port 2 of the first network and port 1 of the second network is terminated with Zi 1.
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The transformed network will have shunt admittances that are dual networks of the series impedances if they were duals in the starting network - which is the case with series inductors and shunt capacitors.
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Any balun placed on the output (antenna) side of a tuner must be built to withstand high voltage and current stresses, because of the wide range of impedances it must handle. For a wide range of frequencies and impedances it may not be possible to build a robust balun that is adequately efficient. For a narrow range of frequencies, using transmission line stubs or sections for impedance transforms (described above) may well be more feasible and will certainly be more efficient.
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J. 22, 269 (1943). for the evaluation of X. Such an implementation of the TTC allows finding a feedback topology even in a network consisting of a voltage source and two impedances in series.
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Currently, headsets are available incorporating dry electrodes with up to 30 channels. Such designs are able to compensate for some of the signal quality degradation related to high impedances by optimizing pre-amplification, shielding and supporting mechanics.
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Several L half-sections may be cascaded to form a composite filter. The most important rule when constructing a composite image filter is that the image impedances must always face an identical impedance; like must always face like. T sections must always face T sections, Π sections must always face Π sections, k-type must always face k-type (or the side of an m-type which has the k-type impedance) and m-type must always face m-type. Furthermore, m-type impedances of different values of m cannot face each other.
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Dual Miller theorem is usually implemented by an arrangement consisting of two voltage sources supplying the grounded impedance Z through floating impedances (see Fig. 3). The combinations of the voltage sources and belonging impedances form the two current sources – the main and the auxiliary one. As in the case of the main Miller theorem, the second voltage is usually produced by a voltage amplifier. Depending on the kind of the amplifier (inverting, non- inverting or differential) and the gain, the circuit input impedance may be virtually increased, infinite, decreased, zero or negative.
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Valves are high voltage/low current devices in comparison with transistors. Tetrode and pentode valves have very flat anode current vs. anode voltage indicating high anode output impedances. Triodes show a stronger relationship between anode voltage and anode current.
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Frequency-dependent impedances may be analyzed by considering the quantities power spectral density and the associated field quantities via the Fourier transform, which allows elimination of the frequency dependence in the analysis by analyzing the system at each frequency independently.
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Ismini Scouras, EE Times. "Variable gain amplifier drives low impedances from one power supply." February 11, 2008. Retrieved July 15, 2011.Ismini Scouras, EE Times. "RF/IF variable-gain amplifier fits wireless infrastructure apps." February 1, 2006. Retrieved July 15, 2011.
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By observing changes in the strength of reflectors, seismologists can infer changes in the seismic impedances. In turn, they use this information to infer changes in the properties of the rocks at the interface, such as density and elastic modulus.
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Feedline impedances are essentially constant for all frequencies up to a very high cut-off frequency far above HF and VHF, where the wavelength becomes ~10× the spacing between the conductors in the line, or smaller. Antenna impedances, however, swing by factors well over 1000:1, with changing frequency, as the antenna passes through an almost evenly-spaced sequence of resonances and "anti-"resonances at different frequencies.Antennas with many different-sized elements can have multiple intermeshed sequences of resonances. The same issue arises if different-sized metal objects are close enough to the antenna or the feedline to couple inductively with either.
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Another drawback of microstrip is that it is more limited than other types in the range of characteristic impedances that it can achieve. Some circuit designs require characteristic impedances of or more. Microstrip is not usually capable of going that high so either those circuits are not available to the designer or a transition to another type has to be provided for the component requiring the high impedance. Microstrip inverted-F antenna The tendency of microstrip to radiate is generally a disadvantage of the type, but when it comes to creating antennae it is a positive advantage.
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Sometimes also antimetrical networks are of interest. These are networks where the input and output impedances are the duals of each other.Matthaei et al, pp. 70-72. ;Lossless network: A lossless network is one which contains no resistors or other dissipative elements.
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It is important that these are connected to a circuit capable of dealing with impedances in the appropriate range and assigning a nominal impedance is a convenient way of quickly determining likely incompatibilities. Loudspeakers and microphones are dealt with in separate sections below.
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Because the transverse deflection can be described with polar coordinates, one may define a deflection or polarization angle using the transverse acceleration voltage components. Polar coordinates are used because it is possible to add up voltage components like vectors, but not shunt impedances.
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The 500 MHz Tektronix TDS510A input impedance is 1M and 10 pF. This allows the use of standard oscilloscope probes.Probes are designed for a specific input impedance. They have compensation adjustments with a limited range, so they often cannot be used on different input impedances.
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If the impedances Za and Zb are duals, and normalised, so that :Z_a.Z_b = 1 then the image impedance ZI becomes a pure resistance. A symmetrical lattice fulfilling this condition is a ‘constant resistance lattice’. Such a lattice, terminated in 1 ohm, is shown below.
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A symmetrical lattice is a two-port electrical wave filter in which diagonally-crossed shunt elements are present - a configuration which sets it apart from ladder networks. The component arrangement of the lattice is shown in the diagram below. The filter properties of this circuit were first developed using image impedance concepts, but later the more general techniques of network analysis were applied to it. There is a duplication of components in the lattice network as the "series impedances" (instances of Za) and "shunt impedances" (instances of Zb) both occur twice, an arrangement that offers increased flexibility to the circuit designer with a variety of responses achievable.
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A multicore cable able to support 25 unbalanced transmission lines In electrical engineering, an unbalanced line is a transmission line, often coaxial cable, whose conductors have unequal impedances with respect to ground; as opposed to a balanced line. Microstrip and single-wire lines are also unbalanced lines.
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An actual wide-band L pad used to match 50 ohms to 75 ohms. An L pad is a network composed of two impedances that typically resemble the letter capital "L" when drawn on a schematic. It is commonly used for attenuation and for impedance matching.
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These impedances will induce wakefields (a strong warping of the electromagnetic field of the beam) that can interact with later particles. Since this interaction may have negative effects, it is studied to determine its magnitude, and to determine any actions that may be taken to mitigate it.
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Valves normally match much higher impedances than that of a loudspeaker. Low-impedance valve types and purpose-designed circuits are required. Reasonable efficiency and moderate Zout (damping factor) can be achieved. These effects mean that OTLs have selective speaker load requirements, just like any other amplifier.
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A taper is a transmission line with a gradual change in cross-section. It can be considered the limiting case of the stepped impedance structure with an infinite number of steps.Zhurbenko, p. 310 Tapers are a simple way of joining two transmission lines of different characteristic impedances.
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The input ports of CMOS oscillators have high impedances, and are thus very susceptible to transient disturbances. According to Ohm's law, high impedance causes high voltage differences. They also are very sensitive to short circuit from moisture or dust. One typical failure is when the oscillators' stability is affected.
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Sony compact disc player CDP- XB930 Operating Instructions. (1). Specifications, p.20. This implies that the input of an average tube amplifier is a problem-free load for music signal sources. By contrast, some transistor amplifiers for home use have lower input impedances, as low as 15 kΩ.
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A different (unrelated) configuration is an impedance matching connection in which the source and load impedances are either equal or complex conjugates. Such a configuration serves to either prevent reflections when transmission lines are involved, or to maximize power delivered to the load given an unchangeable source impedance.
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The passive components containing resistors, capacitors and inductors can be expressed as combination of several impedances or admittances. Another expression method is to regard the passive components of the power converter as a two-port network and use a Y-matrix or Z-matrix to describe the characteristics of passive components.
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The requirement for better matching to the end impedances is one of the main motivations for using composite filters. A section designed to give good matching is used at the ends but something else (for instance stopband rejection or passband to stopband transition) is designed for the body of the filter.
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For instance force/velocity is mechanical impedance. The mobility analogy does not preserve this analogy between impedances across domains, but it does have another advantage over the impedance analogy. In the mobility analogy the topology of networks is preserved, a mechanical network diagram has the same topology as its analogous electrical network diagram.
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If one chooses R1 = R2 and C1 = C2 then Rf = 2 Rb. In practice, the values of R and C will never be exactly equal, but the equations above show that for fixed values in the Z1 and Z2 impedances, the bridge will balance at some ω and some ratio of Rb/Rf.
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In 1980s and early 1990s coaxial cable was also used in computer networking, most prominently in Ethernet networks, where it was later in late 1990s to early 2000s replaced by UTP cables in North America and STP cables in Western Europe, both with 8P8C modular connectors. Micro coaxial cables are used in a range of consumer devices, military equipment, and also in ultra-sound scanning equipment. The most common impedances that are widely used are 50 or 52 ohms, and 75 ohms, although other impedances are available for specific applications. The 50 / 52 ohm cables are widely used for industrial and commercial two-way radio frequency applications (including radio, and telecommunications), although 75 ohms is commonly used for broadcast television and radio.
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The remaining power is converted to heat. The UniValve and BiValve-30 amplifiers have Hot Plates built into them; the Flexi-50 has a foot-switchable master volume control in lieu of a Hot Plate. The Hot Plate is manufactured in five different colors; each color corresponds to the specific amplifier impedance that the Hot Plate is optimized for (the impedances should be matched.) The colors and impedances are: gold- 2 ohms, green- 2.7 ohms, red- 4 ohms, purple- 8 ohms, and blue- 16 ohms. The Hot Plate has a Line Out jack, which can be used to send a DI signal to the mixer, or to insert equalization, time effects, and possibly a solid- state amplifier between the distorting tube power amp and the guitar speaker.
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In telecommunications and professional audio, a balanced line or balanced signal pair is a transmission line consisting of two conductors of the same type, each of which have equal impedances along their lengths and equal impedances to ground and to other circuits.Young EC, The Penguin Dictionary of Electronics, 1988, The chief advantage of the balanced line format is good rejection of external noise when fed to a differential amplifier. Common forms of balanced line are twin-lead, used for radio frequency signals and twisted pair, used for lower frequencies. They are to be contrasted to unbalanced lines, such as coaxial cable, which is designed to have its return conductor connected to ground, or circuits whose return conductor actually is ground.
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As a result of the maximum power theorem, devices transfer maximum power to a load when running at 50% electrical efficiency. This occurs when the load resistance (of the device in question) is equal to the internal Thevenin equivalent resistance of the power source. This is valid only for non-reactive source and load impedances.
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The issue is complex, as part of the change in impedance is due to acoustic loading changes across a driver's passband. On the negative side, passive networks may be bulky and cause power loss. They are not only frequency specific, but also impedance specific. This prevents their interchangeability with speaker systems of different impedances.
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The total impedance of many simple networks of components can be calculated using the rules for combining impedances in series and parallel. The rules are identical to those for combining resistances, except that the numbers in general are complex numbers. The general case, however, requires equivalent impedance transforms in addition to series and parallel.
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He received his S.B. in electrical engineering from MIT in 1941, and upon graduation joined the staff of the MIT Radiation Laboratory. After World War II, Fano continued on to complete his Sc.D. in electrical engineering from MIT in 1947. His thesis, titled "Theoretical Limitations on the Broadband Matching of Arbitrary Impedances", was supervised by Ernst Guillemin.
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The circuit diagrams in this article follow the usual conventions in electronics;Tooley, pp. 258–264 lines represent conductors, filled small circles represent junctions of conductors, open small circles represent terminals for connection to the outside world. In most cases, impedances are represented by rectangles. A practical circuit diagram would use the specific symbols for resistors, inductors, capacitors etc.
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It is not simply double because the noise sources are random and there is some partial cancellation in the combined noise. The noise figure is then 1.414, or 1.5 dB. For higher impedances, such as 250 kΩ, the EF86's voltage noise is 1/101/2 lower than the sources's own noise, and the noise figure is ~1 dB.
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The monopole aspects are relatively fixed. The characteristic dimension L2 of the tube is fixed; the characteristic speed c0 is fixed. The effective length of the tube is fixed, since the radiation impedances at each end are fixed. Unlike the pipe organ, however, these instruments have side ports to change the resonance frequency and thus the acoustical Strouhal number.
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In telecommunication, the term conditioning equipment has the following meanings: # At junctions of circuits, equipment used to obtain desired circuit characteristics, such as matched transmission levels, matched impedances, and equalization between facilities. # Corrective networks used to improve data transmission, such as equalization of the insertion loss-vs.-frequency characteristic and the envelope delay distortion over a desired frequency range.
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The figure below illustrates the problem. A lattice filter, equivalent to two sections of constant-k low-pass filter, has been derived by image methods. (The network is normalised, with and so and . The left-hand figure gives the lattice circuit and the right-hand figure gives the insertion loss with the network terminated (1) resistively, and (2) in its correct characteristic impedances.
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DC calculating boards used resistors and DC sources to represent an AC network. A resistor was used to model the inductive reactance of a circuit, while the actual series resistance of the circuit was neglected. The principle disadvantage was the inability to model complex impedances. However, for short-circuit fault studies, the effect of the resistance component was usually small.
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The copper cables used in SSA configurations are round bundles of two or four twisted pairs, up to 25 metres long and terminated with 9-pin micro-D connectors. Impedances are 75 ohm single-ended, and 150 ohm differential. For longer-distance connections, it is possible to use fiber-optic cables up to 10 km (6 mi) in length. Signals are differential TTL.
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20 There are two other power conjugate systems on the same variables that are in use. The mobility analogy maps mechanical force to electric current instead of voltage. This analogy is widely used by mechanical filter designers and frequently in audio electronics also. The mapping has the advantage of preserving network topologies across domains but does not maintain the mapping of impedances.
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If these impedances are not matched, the antenna will reflect some of the power back toward the transmitter, so not all the power will be radiated. The antenna's radiation resistance is usually the main part of its input resistance, so it determines what impedance matching is necessary and what types of transmission line would be well matched to the antenna.
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Transformers, autotransformers, and baluns are sometimes incorporated into the design of narrow band antenna tuners and antenna cabling connections. They will all usually have little effect on the resonant frequency of either the antenna or the narrow band transmitter circuits, but can widen the range of impedances that the antenna tuner can match, and/or convert between balanced and unbalanced cabling where needed.
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An orthomode transducer (a variety of duplexer) with stepped impedance matching Cascaded lines are lengths of transmission line where the output of one line is connected to the input of the next. Multiple cascaded lines of different characteristic impedances can be used to construct a filter or a wide-band impedance matching network. This is called a stepped impedance structure.Lee, p.
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In addition to this, the tone of a guitar amplifier is generally more defined if the guitar is going direct into the input of the preamplifier. The second advantage is to match impedances of equipment. For example, most guitar rack equipment works better at line-level, and not instrument level. By placing the effects after the preamp, signal loss due to impedance mismatch is avoided.
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Resonant circuits can generate very high voltages. A tesla coil is a high-Q resonant circuit. Electrical resonance occurs in an electric circuit at a particular resonant frequency when the impedances or admittances of circuit elements cancel each other. In some circuits, this happens when the impedance between the input and output of the circuit is almost zero and the transfer function is close to one.
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This is particularly a problem with printed technologies, such as microstrip, when implementing high characteristic impedances. High impedance requires narrow lines and there is a minimum size that can be printed. Very wide lines, on the other hand, allow the possibility of undesirable transverse resonant modes to form. A different length of UE, with a different Z0, may be chosen to overcome these problems.
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RF transformers sometimes used a third coil (called a tickler winding) to inject feedback into an earlier (detector) stage in antique regenerative radio receivers. In RF and microwave systems, a quarter-wave impedance transformer provides a way of matching impedances between circuits over a limited range of frequencies, using only a length of transmission line. The line may be coaxial cable, waveguide, stripline, or microstrip.
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The Miller theorem refers to the process of creating equivalent circuits. It asserts that a floating impedance element, supplied by two voltage sources connected in series, may be split into two grounded elements with corresponding impedances. There is also a dual Miller theorem with regards to impedance supplied by two current sources connected in parallel. The two versions are based on the two Kirchhoff's circuit laws.
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Network synthesis on the other hand, takes care of the termination impedances simply by incorporating them into the network being designed.Matthaei, pp.83–84 The development of network analysis needed to take place before network synthesis was possible. The theorems of Gustav Kirchhoff and others and the ideas of Charles Steinmetz (phasors) and Arthur Kennelly (complex impedance)Arthur E. Kennelly, 1861 – 1939 IEEE biography, retrieved 13 June 2009 laid the groundwork.
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So every two-wire balanced transmission line has two modes which are nominally called the differential and common modes. The circuit shown on the bottom only models the differential mode. In the top circuit, the voltage doublers, the difference amplifiers and impedances Z(s) account for the interaction of the transmission line with the external circuit. This circuit, as depicted, is also fully symmetric, and also not drawn that way.
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In resonant coupling, the source and receiver are tuned to resonate at the same frequency and are given similar impedances. This allows power as well as information to flow from the source to the receiver. Such coupling via the magnetoquasistatic field is called resonant inductive coupling and can be used for wireless energy transfer. Applications include induction cooking, induction charging of batteries and some kinds of RFID tag.
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There are two principle classes of analogy in use. The impedance analogy (also called the Maxwell analogy) preserves the analogy between mechanical, acoustical and electrical impedance but does not preserve the topology of networks. The mechanical network is arranged differently to its analogous electrical network. The mobility analogy (also called the Firestone analogy) preserves network topologies at the expense of losing the analogy between impedances across energy domains.
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An example of a 3-terminal network transform that is not restricted to 2-ports is the Y-Δ transform. This is a particularly important transform for finding equivalent impedances. Its importance arises from the fact that the total impedance between two terminals cannot be determined solely by calculating series and parallel combinations except for a certain restricted class of network. In the general case additional transformations are required.
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Their output impedances have been intentionally developed to approach zero. Due to the nature of vacuum tubes and audio transformers, the output impedance of an average tube amplifier is usually considerably higher than the modern audio amplifiers produced completely without vacuum tubes or audio transformers. Most tube amplifiers with their higher output impedance are less ideal voltage amplifiers than the solid state voltage amplifiers with their smaller output impedance.
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The oscillator is based on a bridge circuit originally developed by Max Wien in 1891 for the measurement of impedances. The bridge comprises four resistors and two capacitors. The oscillator can also be viewed as a positive gain amplifier combined with a bandpass filter that provides positive feedback. Automatic gain control, intentional non-linearity and incidental non-linearity limit the output amplitude in various implementations of the oscillator.
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Example of airborne and structure-borne transmission of sound, where Lp is sound pressure level, A is attenuation, P is acoustical pressure, S is the area of the wall [m²], and τ is the transmission coefficient Acoustic transmission is the transmission of sounds through and between materials, including air, wall, and musical instruments. The degree to which sound is transferred between two materials depends on how well their acoustical impedances match.
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Distribution networks are usually made of a variety of conductor types, and terminating into loads of different impedances, which also vary over time. Such infrastructure results in a communication channel which has a time dependent amplitude and phase response that varies with frequency. Interference and impulsive noise produced by motors, switching power supplies and halogen lamps reduces the reliability of communication signals. Due to line attenuation, the noise is location dependent.
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The basic configuration of the symmetrical lattice is shown in the left-hand diagram. A commonly used short-hand version is shown on the right, with dotted lines indicating the presence the second pair of matching impedances. center It is possible with this circuit to have the characteristic impedance specified independently of its transmission properties,Zverev A.I., "Handbook of Filter Synthesis", Wiley N.Y., 1967, (p.6) a feature not available to ladder filter structures.
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IEC 60958 Type II defines an unbalanced electrical or optical interface for consumer electronics applications. The precursor of the IEC 60958 Type II specification was the Sony/Philips Digital Interface, or S/PDIF. Both were based on the original AES/EBU work. S/PDIF and AES3 are interchangeable at the protocol level, but at the physical level, they specify different electrical signalling levels and impedances, which may be significant in some applications.
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By keeping output impedances low, Serge largely avoided the need for screened cables. 3.5 mm sockets were used for some audio interfacing to external equipment. Serge modules did not separate audio signal and control voltage jacks, all signals were patched from module to module via banana patch cords. Banana cables are most flexible in electronic patching and offer quick patching with a secure connection, most banana jacks can be stacked as well.
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An advantage of using mm'-types for impedance matching is that these type of end sections will have a fast transition anyway (much more so than m=0.6 m-type) because mm'=0.3 for impedance matching. So the need for sections in the body of the filter to do this may be dispensed with. Typical example of a composite image filter in block diagram form. The image impedances and how they match are shown.
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For this to be feasible, the 5V source impedance and 3.3V input impedance must be negligible, or they must be constant and the divider resistor values must account for their impedances. If the input impedance is capacitive, a purely resistive divider will limit the data rate. This can be roughly overcome by adding a capacitor in series with the top resistor, to make both legs of the divider capacitive as well as resistive.
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Zobel found that using these impedances constructed out of small filter chains as components in a greater network allowed him to build realistic line simulators. These were not in any sense intended as practical filters in the field, but rather the intention was to construct good controllable line simulators without having the inconvenience of miles of cable to contend with.Zobel, O J, Selective Constant-Resistance Network, , filed 13 April 1928, issued 20 Aug 1929.
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He realized very early on that mismatched impedances inevitably meant reflections, and reflections meant a loss of signal. Improving the impedance match, conversely, would automatically improve a filter's pass-band response. This impedance matching approach not only led to better filters but the techniques developed could be used to construct circuits whose sole purpose was to match together two disparate impedances.Zobel, O J, Electrical Wave Filter, , filed 9 June 1923, issued 25 Jan 1927.
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In June 1926 Cauer presented his thesis paper, The realisation of impedances of specified frequency dependence, at the Institute of Applied Mathematics and Mechanics of the Technical University of Berlin. This paper is the beginning of modern network synthesis.Belevitch, p850 In 1927 Cauer went to work as a research assistant at Richard Courant's Institute of Mathematics at the University of Göttingen. In 1928 he obtained his habilitation and became an external university lecturer.
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Active filters have good isolation between stages, and can provide high input impedance and low output impedance; this makes their characteristics independent of the source and load impedances. Multiple stages can be cascaded when desired to improve characteristics. In contrast, design of multiple-stage passive filters must take into account each stage's frequency-dependent loading of the preceding stage. It is feasible to make active filters tunable over a wide range, compared with passive filters.
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The electric power systems analysis could be conducted using network theory from two main points of view: (1) an abstract perspective (i.e., as a graph consists from nodes and edges), regardless of the electric power aspects (e.g., transmission line impedances). Most of these studies focus only on the abstract structure of the power grid using node degree distribution and betweenness distribution, which introduces substantial insight regarding the vulnerability assessment of the grid.
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When using the method of symmetrical components, separate one-line diagrams are made for each of the positive, negative and zero-sequence systems. This simplifies the analysis of unbalanced conditions of a polyphase system. Items that have different impedances for the different phase sequences are identified on the diagrams. For example, in general a generator will have different positive and negative sequence impedance, and certain transformer winding connections block zero-sequence currents.
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Usually analysis of a three-phase system is simplified by assuming balanced loading of all three phases. Steady-state operation is assumed, with no transient changes in power flow or voltage due to load or generation changes. The system frequency is also assumed to be constant. A further simplification is to use the per-unit system to represent all voltages, power flows, and impedances, scaling the actual target system values to some convenient base.
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The two stimulation methods may result in significantly different results. Few studies have attempted to correlate chronaxie times with sensory perception, although understanding the neural elements that are involved in a subjective percept, such as tingling, has important physiological implications. The measurements were taken with different types of electrodes and with stimulators having unknown output impedances. The chronaxie values for human arm sensory nerves range from 0.35 to 1.17 ms, a ratio of 3.3.
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In contrast to two-element L-networks, the circuits described below all have three or more components, and hence have many more choices for inductance and capacitance that will produce an impedance match. The radio operator must experiment, test, and use judgement to choose among the many adjustments that match the same impedances. This section discusses circuit designs for unbalanced lines; it is followed by a section that discusses tuners for balanced lines.
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An SWR meter does not measure the actual impedance of a load (the resistance and reactance), but only the mismatch ratio. To measure the actual impedance requires an antenna analyzer or other similar RF measuring device. For accurate readings, the SWR meter itself must also match the line's impedance (typically 50 or 75 Ohms). To accommodate multiple impedances, some SWR meters have switches that select the impedance appropriate for the sense lines.
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Filters are required to operate at many different frequencies, impedances and bandwidths. The utility of a prototype filter comes from the property that all these other filters can be derived from it by applying a scaling factor to the components of the prototype. The filter design need thus only be carried out once in full, with other filters being obtained by simply applying a scaling factor. Especially useful is the ability to transform from one bandform to another.
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From a T-section, the series Z and shunt Y are multiplied by an arbitrary parameter m . An additional impedance is then inserted in series with Y whose value is that which restores the original image impedance. The half-sections resulting from splitting the T-section, however, will show a different image impedance at the split, `ZiΠm`. Two such half-sections cascaded with the `ZiT` impedances facing, will form a `Π`-section with image impedance `ZiΠm`.
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This will most usually mean termination with the system nominal impedance which, in turn, is usually chosen to equal the nominal characteristic impedance of the system transmission lines. This is the impedance the circuit is expected to be connected to in operation and impedance matching is of some importance in telecommunications. In some design contexts a more theoretical impedance is considered such as image impedance. A symmetric network will have two equal input impedances, Zi1 and Zi2.
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The electrical signal generated by the coil travels back along the speaker cable to the amplifier. Well-designed amplifiers have low output impedance so that this generated signal has little effect on the amplifier. Characteristically, solid state amplifiers have had much lower output impedances than tube amplifiers. So much so that differences in practice between a 16 ohm nominal impedance driver and a 4 ohm nominal impedance driver have not been important enough to adjust for.
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Consequently, the overall insertion loss of a cascade of constant resistance sections is simply to sum total of the individual sections. Conversely, a given complicated transfer impedance may be decomposed into multiplicative factors, whose individual lattice realizations, when connected in cascade, represent a synthesis of that transfer impedance. So, although it is possible to synthesize a single lattice with complicated impedances Za and Zb, it is practically easier to construct and align a cascade of simpler circuits.
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In practice, systems rarely have perfectly balanced loads, currents, voltages and impedances in all three phases. The analysis of unbalanced cases is greatly simplified by the use of the techniques of symmetrical components. An unbalanced system is analysed as the superposition of three balanced systems, each with the positive, negative or zero sequence of balanced voltages. When specifying wiring sizes in a three-phase system, we only need to know the magnitude of the phase and neutral currents.
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Wilhelm Cauer The field of network synthesis was founded by German mathematician and scientist Wilhelm Cauer (1900–1945). The first hint towards a theory came from American mathematician Ronald M. Foster (1896–1998) when he published A reactance theorem in 1924. Cauer immediately recognised the importance of this work and set about generalising and extending it. His thesis in 1926 was on "The realisation of impedances of specified frequency dependence" and is the beginning of the field.
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The image method, therefore, relies on each filter section being terminated with the correct image impedance. This is easy enough to do with the internal sections of a multiple section filter, because it is only necessary to ensure that the sections facing the one in question have identical image impedances. However, the end sections are a problem. They will usually be terminated with fixed resistances that the filter cannot match perfectly except at one specific frequency.
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One-element-kind networks can be thought of as a special case of two-element-kind. It is possible to use the transformations in this section on a certain few 3-element-kind networks by substituting a network of elements for element Zn. However, this is limited to a maximum of two impedances being substituted; the remainder will not be a free choice. All the transformation equations given in this section are due to Otto Zobel.Zobel, 1923.
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The Wilkinson power divider solves the matching problem of the simple T-junction: it has low VSWR at all ports and high isolation between output ports. The input and output impedances at each port are designed to be equal to the characteristic impedance of the microwave system. This is achieved by making the line impedance \scriptstyle \sqrt 2 of the system impedance – for a system the Wilkinson lines are approximately Dyer, p.480 Räisänen and Lehto, p.
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This can be advantageous because precision resistors of the value of the system impedance are always available for most system nominal impedances. The tee circuit has the benefits of simplicity, low cost, and intrinsically wide bandwidth. It has two major drawbacks; first, the circuit will dissipate power since it is resistive: an equal split will result in insertion loss instead of . The second problem is that there is directivity leading to very poor isolation between the output ports.
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A feedback voltage amplifier using an op amp with finite gain but infinite input impedances and zero output impedance.See, for example, Figure 1.4, p. 7 Ideal op amp model in or The operational amplifier was originally developed as a building block for the construction of analog computers, but is now used almost universally in all kinds of applications including audio equipment and control systems. Operational amplifier circuits typically employ negative feedback to get a predictable transfer function.
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Changing inverter impedances can change voltage fluctuations of DG, meaning inverters have the ability to control DG voltage output. To reduce the effect of DG integration on mechanical grid equipment, transformers and load tap changers have the potential to implement specific tap operation vs. voltage operation curves mitigating the effect of voltage irregularities due to DG. That is, load tap changers respond to voltage fluctuations that last for a longer period than voltage fluctuations created from DG equipment.
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Longer antennas may have impedances that are more advantageous unless the electrical height exceeds about of a wavelength. In any case, an electrical network at the base of the tower matches the antenna to its transmission line. If the tower is very short, it will have its capacitive reactance tuned out by this matching network. This network and tower combination often results in a narrow bandwidth, severely limiting the audio frequency fidelity of the radio station.
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The hot and cold connections are often shown as In+ and In− ("in plus" and "in minus") on circuit diagrams. The term balanced comes from the method of connecting each wire to identical impedances at source and load. This means that much of the electromagnetic interference will induce an equal noise voltage in each wire. Since the amplifier at the receiving end measures the difference in voltage between the two signal lines, noise that is identical on both wires is rejected.
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There are many methods used to determine passive elements. The conventional method is to switch off the power converter and measure the impedance with an impedance analyzer, or measure the scattering parameters by a vector network analyzer and compute the impedance afterwards. These conventional methods assume that the impedances of power converter is the same in the operating condition and switched-off condition. Many state-of-art methods are investigated to measure the impedance when the power converter is in operating condition.
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These networks arise often in 3-phase power circuits as they are the two most common topologies for 3-phase motor or transformer windings. Figure 1.6An example of this is the network of figure 1.6, consisting of a Y network connected in parallel with a Δ network. Say it is desired to calculate the impedance between two nodes of the network. In many networks this can be done by successive applications of the rules for combination of series or parallel impedances.
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The resonance frequency is defined as the frequency at which the impedance of the circuit is at a minimum. Equivalently, it can be defined as the frequency at which the impedance is purely real (that is, purely resistive). This occurs because the impedances of the inductor and capacitor at resonance are equal but of opposite sign and cancel out. Circuits where L and C are in parallel rather than series actually have a maximum impedance rather than a minimum impedance.
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Schematic view of the interior of Earth. The core–mantle boundary (CMB in the parlance of solid earth geophysicists) of the Earth lies between the planet's silicate mantle and its liquid iron-nickel outer core. This boundary is located at approximately 2891 km (1796 mi) depth beneath the Earth's surface. The boundary is observed via the discontinuity in seismic wave velocities at that depth due to the differences between the acoustic impedances of the solid mantle and the molten outer core.
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The second is to find the canonical (minimal) forms of these functions and the relationships (transforms) between different forms representing the same transfer function. Finally, it is not, in general, possible to find an exact finite-element solution to an ideal transfer function - such as zero attenuation at all frequencies below a given cutoff frequency and infinite attenuation above. The third task is therefore to find approximation techniques for achieving the desired responses. Initially, the work revolved around one-port impedances.
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The more sections there are in the coupler, the higher is the ratio of impedances of the branch lines. High impedance lines have narrow tracks and this usually limits the design to three sections in planar formats due to manufacturing limitations. A similar limitation applies for coupling factors looser than ; low coupling also requires narrow tracks. Coupled lines are a better choice when loose coupling is required, but branch-line couplers are good for tight coupling and can be used for hybrids.
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Not only does it take better account of the terminal impedances but the designer has additional degrees of freedom allowing improved matching. The size and gaps of the teeth are tapered in this method of design. That is, the teeth can be different sizes according to their position in the filter, compared with an image design where all sections are identical. With this approach, the original specification for passband and stopband can be kept while simultaneously improving the impedance matching.
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Loudspeaker impedances are kept relatively low compared with other audio components so that the required audio power can be transmitted without using inconveniently (and dangerously) high voltages. The most common nominal impedance for loudspeakers is 8 Ω. Also used are 4 Ω and 16 Ω.Ballou, p.523. The once common 16 Ω is now mostly reserved for high frequency compression drivers since the high frequency end of the audio spectrum does not usually require so much power to reproduce.Vasey, pp.34–35.
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A half-wavelength folded dipole, commonly seen on television antennae, on the other hand, has a 288 Ω impedance - four times that of a straight-line dipole. The ½ λ dipole and the ½ λ folded dipole are commonly taken as having nominal impedances of 75 Ω and 300 Ω, respectively.Gulati, p.426. An installed antenna’s feed-point impedance varies above and below the quoted value, depending on its installation height above the ground and the electrical properties of the surrounding earth.
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When a pulse is launched into the microstrip by the transmitter, its amplitude depends on the ratio of the impedances of the transmitter and the microstrip. The impedance of the transmitter is simply its output resistance. The impedance of the microstrip is its characteristic impedance, which depends on its dimensions and on the materials used in the backplane's construction. As the leading edge of the pulse (the incident wave) passes the receiver, it may or may not have sufficient amplitude to be detected.
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In polyphase electrical systems, generally phase-to-phase, phase-to-ground (earth), and phase-to-neutral faults are examined, as well as a case where all three phases are short-circuited. Because impedances of cables or devices varies between phases, the prospective short-circuit current varies depending on the type of fault. Protection devices in the system must respond to all three cases. The method of symmetrical components is used to simplify analysis of unsymmetrical faults in three-phase systems.
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This makes accurate analysis of results from a small number of electrodes difficult and unreliable. Identifying zones with specific impedances can provide greater certainty regarding the factors behind the impedance. Conventional Four Electrode or Tetra-polar Impedance Measurement (TPIM) is simple, but the zone of sensitivity is not well defined and may include organs other that those of interest, making interpretation difficult and unreliable. On the other hand, Electrical impedance tomography (EIT) offers reasonable resolution, but is complex and require many electrodes.
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The illustration shows two versions of essentially the same circuit: Series cap with taps and an alternate configuration For low-Z lines. Series cap with taps (middle, left) adds a series capacitor to the input side of the Fixed link with taps. The input capacitor allows fine adjustment with fewer taps on the main coil. An alternate connection (middle, right) for the series cap circuit is useful for low impedances only, but avoids the taps (For low-Z lines in the illustration).
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In the video, the green LED shows the dial impulse pulses and the red LED shows the dial's off-normal contact function. Off-normal contacts typically serve two additional functions. They may implement a shunt across the transmitter circuit and induction coil to maximize the pulsing signal of the dial by eliminating all internal impedances of the telephone set. Another function is to short-circuit the telephone receiver during dialing, to prevent audible clicking noise from being heard by the telephone user.
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In direct coupled OTL designs, both the necessary blocking of DC and matching of impedances are accomplished, respectively, through the topology of the amplifier's output section and the selection of vacuum tube types with sufficiently low impedance to allow effective power transfer to the loudspeaker. Typically, direct coupled OTL amplifiers will have a user- adjustable DC offset control, which allows the user to trim off any residual DC voltage residing at the amplifier's output terminals prior to operation. Servo-controlled variants also exist.
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The original electronic apex locators operated on the direct current principle. A problem with these devices was that conductive fluids such as hemorrhage, exudate, or irrigant in the canal would permit current flow and therefore a false reading. Newer devices are impedance-based, using alternating current of two frequencies;these measure and compare two electrical impedances that change as the file moves apically. The benefit is that these devices are much less affected by fluid conductive media in the canal.
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Slotline variants: A, standard, B, antipodal, C, bilateral Antipodal slotline is used where very low characteristic impedances are required. With dielectric lines, low impedance means narrow lines (the opposite of the case with conducting lines) and there is a limit to the thinness of line that can be achieved because of the printing resolution. With the antipodal structure, the conductors can even overlap without any danger of short-circuiting. Bilateral slotline has advantages similar to those of bilateral air stripline.
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It is also free of radiation since it is completely enclosed in the rectangular waveguide. A metal insert device has an even lower loss because it is air dielectric, but has very limited circuit complexity. A full waveguide solution for a complex design retains the low loss of air dielectric, but it would be much bulkier than finline and significantly more expensive to manufacture. A further advantage of finline is that it can achieve a particularly wide range of characteristic impedances.
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An ideal current source has an infinite output impedance in parallel with the source. A real- world current source has a very high, but finite output impedance. In the case of transistor current sources, impedances of a few megohms (at low frequencies) are typical. An ideal current source cannot be connected to an ideal open circuit because this would create the paradox of running a constant, non-zero current (from the current source) through an element with a defined zero current (the open circuit).
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Antimetrical, in this context, means that the filter image impedances and terminations at each end are the dual of each other. This will be the case if the filter has a series and shunt section of the same type, respectively, at each end. Symmetrical filters have an even number of half-sections and antimetrical filters have an odd number of half-sections. In the vast majority of cases the filter design will be either symmetrical or antimetrical and one of these reduced expressions will apply.
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However, a single length of transmission line can only be precisely λ/4 long at its resonant frequency and there is consequently a limit to the bandwidth over which it will work. There are more complex kinds of inverter circuit that more accurately invert impedances. There are two classes of inverter, the J-inverter, which transforms a shunt admittance into a series impedance, and the K-inverter which does the reverse transformation. The coefficients J and K are respectively the scaling admittance and impedance of the converter.
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Damping factor (ratio of output impedance (amplifier) to input impedance (driver voice coil)) are adequate in either case for well- designed amplifiers. Tube amplifiers have sufficiently higher output impedances that they normally included multi-tap output transformers to better match to the driver impedance. Sixteen ohm drivers (or loudspeakers systems) would be connected to the 16-ohm tap, 8 ohm to the 8 ohm tap, etc. This is significant since the ratio between the loudspeaker impedance and the amplifier's impedance at a particular frequency provides damping (i.e.
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An example of a transmission line modeled by this circuit would be a balanced transmission line such as a telephone line. The impedances Z(s), the voltage dependent current sources (VDCSs) and the difference amplifiers (the triangle with the number "1") account for the interaction of the transmission line with the external circuit. The T(s) blocks account for delay, attenuation, dispersion and whatever happens to the signal in transit. One of the T(s) blocks carries the forward wave and the other carries the backward wave.
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The other leg is the unknown – either an antenna or a reactive component. To measure impedance, the bridge is adjusted, so that the two legs have the same impedance. When the two impedances are the same, the bridge is balanced. Using this circuit it is possible to either measure the impedance of the antenna connected between ANT and GND, or it is possible to adjust an antenna, until it has the same impedance as the network on the left side of the diagram below.
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An alternating current power-flow model is a model used in electrical engineering to analyze power grids. It provides a nonlinear system which describes the energy flow through each transmission line. The problem is non-linear because the power flow into load impedances is a function of the square of the applied voltages. Due to nonlinearity, in many cases the analysis of large network via AC power-flow model is not feasible, and a linear (but less accurate) DC power-flow model is used instead.
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Aperture theory is important for waveguide cavity filters, which were first developed at Rad Lab. Their work was published after the war in 1948 and includes an early description of dual-mode cavities by Fano and Lawson. Theoretical work following the war included the commensurate line theory of Paul Richards. Commensurate lines are networks in which all the elements are the same length (or in some cases multiples of the unit length), although they may differ in other dimensions to give different characteristic impedances.
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This line is intended for use with RF circuits, particularly antennae. Transmission of a signal over a balanced line reduces the influence of noise or interference due to external stray electric fields. Any external signal sources tend to induce only a common mode signal on the line, and the balanced impedances to ground minimizes differential pickup due to stray electric fields. The conductors are sometimes twisted together to ensure that each conductor is equally exposed to any external magnetic fields that could induce unwanted noise.
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Classically, both dynamic and condenser microphones used transformers to provide a differential-mode signal. While transformers are still used in the large majority of modern dynamic microphones, more recent condenser microphones are more likely to use electronic drive circuitry. Each leg, irrespective of any signal, should have an identical impedance to ground. Pair cable (or a pair-derivative such as star quad) is used to maintain the balanced impedances and close twisting of the cores ensures that any interference is common to both conductors.
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An impedance analyzer is a type of electronic test equipment used to measure complex electrical impedance as a function of test frequency. Impedance is an important parameter used to characterize electronic components, electronic circuits, and the materials used to make components. Impedance analysis can also be used to characterize materials exhibiting dielectric behavior such as biological tissue, foodstuffs or geological samples. Impedance analyzers come in three distinct hardware implementations, and together these three implementations can probe from ultra low frequency to ultra high frequency and can measure impedances from µΩ to TΩ.
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Transmission lines and certain types of filter design use the image method to determine their transfer parameters. In this method, the behaviour of an infinitely long cascade connected chain of identical networks is considered. The input and output impedances and the forward and reverse transmission functions are then calculated for this infinitely long chain. Although the theoretical values so obtained can never be exactly realised in practice, in many cases they serve as a very good approximation for the behaviour of a finite chain as long as it is not too short.
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Linear array transducer Ultrasonography (sonography) uses a probe containing multiple acoustic transducers to send pulses of sound into a material. Whenever a sound wave encounters a material with a different density (acoustical impedance), part of the sound wave is reflected back to the probe and is detected as an echo. The time it takes for the echo to travel back to the probe is measured and used to calculate the depth of the tissue interface causing the echo. The greater the difference between acoustic impedances, the larger the echo is.
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For any given desired bandform there are two classes of mn transformation that can be applied, namely, the mid-series and mid-shunt derived sections; this terminology being more fully explained in the m-derived filter article. Another feature of m-type filters that also applies in the general case is that a half section will have the original k-type image impedance on one side only. The other port will present a new image impedance. The two transformations have equivalent transfer functions but different image impedances and circuit topology.
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This method is based on the two assumptions mentioned in section Assumption, so the system is regarded as linear time-invariant system. Based on these assumptions, the equivalent circuit could be derived from several equations of different operating conditions. The equivalent circuit model is defined containing three impedances and two current sources, where five unknown parameters needs to be determined. Three sets of different operating conditions are built up by changing external impedance and the corresponding currents and voltages at the terminals of the power converter are measured or simulated as known parameters.
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All high-order lattice networks can be replaced by a cascade of simpler lattices, provided their characteristic impedances are all equal to that of the original and the sum of their propagation functions equals the original. In the particular case of all-pass networks (networks which modify the phase characteristic only), any given network can always be replaced by a cascade of second-order lattices together with, possibly, one single first order lattice. Whatever the filter requirements being considered, the reduction process results in simpler filter structures, with less stringent demands on component tolerances.
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Matthaei et al., pp. 3-5 The designer first prescribes the frequency band over which the matching network is to operate, and then designs a band-pass filter for that band. The only essential difference between a standard filter and a matching network is that the source and load impedances are not equal.Matthaei et al., p. 681 However, there are differences in which parameters are important. Unless the network has a dual function, the designer is not too concerned over the behaviour of the impedance matching network outside the passband.
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One of E-meter's primary components is a Wheatstone bridge, an electrical circuit configuration invented in 1833"The Genesis of the Wheatstone Bridge" by Stig Ekelof discusses Christie's and Wheatstone's contributions, and why the bridge carries Wheatstone's name. Published in "Engineering Science and Education Journal", volume 10, no 1, February 2001, pages 37-40. that enables the detection of very small differences between two electrical impedances (in this case, resistances). The E-meter is constructed so that one resistance is the subject's body and the other is a rheostat controlled by the operator.
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Particularly with a transmitting antenna, the antenna feed is a critical component that must be adjusted to function compatibly with the antenna and transmitter. Each type of transmission line and each type of antenna has a specific characteristic impedance, which is the ratio of voltage to current that is the "favorite" of the antenna, or line, or radio. Typically the impedances of radios and feedlines are constant.Only the rate of power loss in transmission lines noticeably changes with frequency: The ratio of voltage to current remains constant, even as the power-loss piles up.
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If these impedances are not matched it can cause a condition called standing waves on the feed line, in which the RF energy is reflected back toward the transmitter, wasting energy and possibly overheating the transmitter. This adjustment is done with a device called an antenna tuner in the transmitter, and sometimes a matching network at the antenna. The degree of mismatch between the feedline and the antenna is measured by an instrument called an SWR meter (standing wave ratio meter), which measures the standing wave ratio (SWR) on the line.
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In 1933, Brune was working on his doctoral thesis entitled, Synthesis of Passive Networks and Cauer suggested that he provide a proof of the necessary and sufficient conditions for the realisability of multi-port impedances. Cauer himself had found a necessary condition but had failed to prove it to be sufficient. The goal for researchers then was "to remove the restrictions implicit in the Foster-Cauer realisations and find conditions on Z equivalent to realisability by a network composed of arbitrary interconnections of positive-valued R, C and L."Willems et al., p.
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Karl Willy Wagner (22 February 1883 – 4 September 1953) was a German pioneer in the theory of electronic filters. He is noted by Hendrik Bode as being one of two Germans whose;Bode, H W, Network Analysis and Feedback Amplifier Design, Robert E Krieger Publishing, 1975. The other German being referred to is Wilhelm Cauer. Wagner was the second referee on Cauer's milestone 1926 thesisCauer, W, "Die Verwirklichung der Wechselstromwiderstände vorgeschriebener Frequenzabhängigkeit" ("The realisation of impedances of specified frequency dependence"), Archiv für Elektrotechnic, vol 17, pp355-388, 1926.
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Commensurate lines are networks in which all the elements are the same length (or in some cases multiples of the unit length), although they may differ in other dimensions to give different characteristic impedances. Richards' transformation allows a lumped element design to be taken "as is" and transformed directly into a distributed-element design using a very simple transform equation.Levy and Cohn, p.1056. The difficulty with Richards' transformation from the point of view of building practical filters was that the resulting distributed-element design invariably included series connected elements.
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By the time the waveform is completed and returns to zero, the signal will be out of phase. The main advantage to this approach is that the shift in phase will occur even if the load exactly matches the supply in terms of Ohm's law - the NDZ is based on power factors of the island, which are very rarely 1. The downside is that many common events, like motors starting, also cause phase jumps as new impedances are added to the circuit. This forces the system to use relatively large thresholds, reducing its effectiveness.
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Just as the acoustic energy was transmitted through the air as pressure differentials (or deformations), the acoustic energy travels through the material which makes up the wall in the same manner. Deformation causes mechanical losses via conversion of part of the sound energy into heat, resulting in acoustic attenuation, mostly due to the wall's viscosity. Similar attenuation mechanisms apply for the air and any other medium through which sound travels. The fraction of sound absorbed is governed by the acoustic impedances of both media and is a function of frequency and the incident angle.
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The lines have the same impedance to ground, so the interfering fields or currents induce the same voltage in both wires. Since the receiver responds only to the difference between the wires, it is not influenced by the induced noise voltage. If a balanced line is used in an unbalanced circuit, with different impedances from each conductor to ground, currents induced in the separate conductors will cause different voltage drops to ground, thus creating a voltage differential, making the line more susceptible to noise. Examples of twisted pairs include category 5 cable.
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Most explanations of balanced lines assume symmetric (antiphase) signals but this is an unfortunate confusion—signal symmetry and balanced lines are quite independent of each other. Essential in a balanced line is matched impedances in the driver, line and receiver. These conditions ensure that external noise affects each leg of the differential line equally and thus appears as a common mode signal that is removed by the receiver. There are balanced drive circuits that have excellent common-mode impedance matching between "legs" but do not provide symmetric signals.
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A popular form of specifying the small signal equivalent circuit amongst transistor manufacturers is to use the two-port network parameters known as [h] parameters. These are a matrix of four parameters as with the [z] parameters but in the case of the [h] parameters they are a hybrid mixture of impedances, admittances, current gains and voltage gains. In this model the three terminal transistor is considered to be a two port network, one of its terminals being common to both ports. The [h] parameters are quite different depending on which terminal is chosen as the common one.
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Primarily in abdominal imaging, tissue harmonic imaging (THI) gets more and more valued and used additionally to conventional ultrasonography. THI involves the use of harmonic frequencies that originate within the tissue as a result of nonlinear wave front propagation and are not present in the incident beam. These harmonic signals may arise differently at anatomic sites with similar impedances and thus lead to higher contrast resolution.” Along with higher contrast resolution it has an elevated signal-to-noise ratio and significantly reduced inter- and intraobserver variability compared with conventional US. Additionally it is possible to nearly eliminate ordinary US artifacts, i.e.
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Often a feasibility study using the wells logs will indicate whether separation of the desired lithotype can be achieved with P-impedance alone or whether S-impedance is also required. This will dictate whether a pre- or post-stack inversion is needed. Simultaneous Inversion (SI) is a pre-stack method that uses multiple offset or angle seismic sub-stacks and their associated wavelets as input; it generates P-impedance, S-impedance and density as outputs (although the density output resolution is rarely as high as the impedances). This helps improve discrimination between lithology, porosity and fluid effects.
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Figure 4: NPN voltage follower with current source biasing suitable for integrated circuits The low output impedance allows a source with a large output impedance to drive a small load impedance; it functions as a voltage buffer. In other words, the circuit has current gain (which depends largely on the hFE of the transistor) instead of voltage gain, because of its characteristics it is preferred in many electronic devices. A small change to the input current results in much larger change in the output current supplied to the output load. One aspect of buffer action is transformation of impedances.
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In the power systems analysis field of electrical engineering, a per-unit system is the expression of system quantities as fractions of a defined base unit quantity. Calculations are simplified because quantities expressed as per-unit do not change when they are referred from one side of a transformer to the other. This can be a pronounced advantage in power system analysis where large numbers of transformers may be encountered. Moreover, similar types of apparatus will have the impedances lying within a narrow numerical range when expressed as a per-unit fraction of the equipment rating, even if the unit size varies widely.
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The characteristic impedance of the cable (Z_0) is determined by the dielectric constant of the inner insulator and the radii of the inner and outer conductors. In radio frequency systems, where the cable length is comparable to the wavelength of the signals transmitted, a uniform cable characteristic impedance is important to minimize loss. The source and load impedances are chosen to match the impedance of the cable to ensure maximum power transfer and minimum standing wave ratio. Other important properties of coaxial cable include attenuation as a function of frequency, voltage handling capability, and shield quality.
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Provided that the source and receiver impedances in a circuit are equal (it is balanced), external electromagnetic interference tends to affect both conductors identically. Since the receiving circuit only detects the difference between the wires, the technique resists electromagnetic noise compared to one conductor with an un-balanced reference (low-Ω connection to ground). Contrary to popular belief, differential signalling does not affect noise cancellation. Balanced lines with differential receivers will reject noise regardless of whether the signal is differential or single-ended, but since balanced line noise rejection requires a differential receiver anyway, differential signalling is often used on balanced lines.
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Zobel, O J, Electrical Network, , filed 9 Sept 1926, issued 16 July 1929.Zobel, O J, Electrical Network, , filed 15 Dec 1922, issued 6 July 1926. Zobel used a design technique based on his theoretical discovery that the impedance looking into the end of a filter chain was practically the same (within the limits of component tolerances) as the theoretical impedance of an infinite chain after only a small number of sections had been added to the chain. These "image" impedances have a mathematical characterization impossible to construct simply out of discrete components, and can only ever be approximated.
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94 Transducers have (at leastPiezoelectric transducers are frequently modelled as three-port devices, one electrical and two mechanical, because mechanical vibrations are induced on both sides of the crystal (Cheeke, pp. 213-214).) two ports, one port in the mechanical domain and one in the electrical domain, and are analogous to electrical two-port networks. This is to be compared to the elements discussed so far which are all one-ports. Two-port networks can be represented as a 2×2 matrix, or equivalently, as a network of two dependent generators and two impedances or admittances.
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A bright spot primarily results from the increase in acoustic impedance contrast when a hydrocarbon (with a lower acoustic impedance) replaces the brine-saturated zone (with a higher acoustic impedance) that underlies a shale (with a higher acoustic impedance still), increasing the reflection coefficient. The effect decreases with depth because compaction for sands and shales occurs at different rates and the acoustic impedance relationship stated above will not hold after a certain depth/age. Below this depth, there will be a crossover of shale and sand acoustic impedances and a dim spot is more useful to hydrocarbon exploration.
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Dipoles whose length is approximately half the wavelength of the signal are called half-wave dipoles and are widely used as such or as the basis for derivative antenna designs. These have a radiation resistance which is much greater, closer to the characteristic impedances of available transmission lines, and normally much larger than the resistance of the conductors, so that their efficiency approaches 100%. In general radio engineering, the term dipole, if not further qualified, is taken to mean a center-fed half-wave dipole. Feedpoint impedance of (near-) half-wave dipoles versus electrical length in wavelengths.
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A digital horn analyzer performs a frequency sweep while monitoring the current flowing through the device under test, in order to detect the resonance and anti-resonance frequencies and their respective electrical impedances. The anti-resonance is the frequency at which the current encounters maximum impedance, and the resonance is the frequency of minimum impedance. In analog microampere-meter-based horn analyzers, the user identifies the frequencies manually, using the meter to detect the points of minimum and maximum current while sweeping the driving frequency. In digital analyzers, frequency detection and impedance calculation are performed automatically through embedded software.
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Other technical drawbacks of mercury included its weight, its cost, and its toxicity. Moreover, to get the acoustic impedances to match as closely as possible, the mercury had to be kept at a constant temperature. The system heated the mercury to a uniform above-room temperature setting of 40 °C (104 °F), which made servicing the tubes hot and uncomfortable work. (Alan Turing proposed the use of gin as an ultrasonic delay medium, claiming that it had the necessary acoustic properties.) A considerable amount of engineering was needed to maintain a "clean" signal inside the tube.
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The operation of the DA can perhaps be most easily understood when explained in terms of the traveling-wave tube amplifier (TWTA). The DA consists of a pair of transmission lines with characteristic impedances of Z0 independently connecting the inputs and outputs of several active devices. An RF signal is thus supplied to the section of transmission line connected to the input of the first device. As the input signal propagates down the input line, the individual devices respond to the forward traveling input step by inducing an amplified complementary forward traveling wave on the output line.
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The limiting factor for this method is the input impedance of the voltage buffer, the JFET or CMOS op-amps typically used may have input impedances of many teraohms which is sufficient for most applications. Care must also be taken to ensure there are no unexpected paths by which leakage current may be encountered as this will defeat the system, and extra care must be taken in the design of the amplifier/buffer circuit to prevent oscillation as the guard, especially if it is used over a coaxial cable, may have a strong capacitive coupling to the input.
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In analog systems (including systems that use digital recording but make the copy over an analog connection), generation loss is mostly due to noise and bandwidth issues in cables, amplifiers, mixers, recording equipment and anything else between the source and the destination. Poorly adjusted distribution amplifiers and mismatched impedances can make these problems even worse. Repeated conversion between analog and digital can also cause loss. Generation loss was a major consideration in complex analog audio and video editing, where multi-layered edits were often created by making intermediate mixes which were then "bounced down" back onto tape.
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Cross section of a three conductor transmission line composed of two parallel plates and a rectangular shield. The figure shows the cross section of a three conductor transmission line. The structure has two transmission eigen-modes which are the differential mode (conductors a and b driven with equal amplitude but opposite phase voltages with respect to conductor c) and the common mode (conductors a and b driven with the same voltages with respect to conductor c). 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.
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Following the establishment of NRS 453, broad language in the statute prevented the erection of a state licensure program for commercial businesses. Personal cultivation of marijuana for private medicinal use was the only available means of consumption, with a maximum of 12 plants allowed Following the passage of NRS 453, medical marijuana advocates and commercial business owners criticized the Nevada's slow handling of the legislative and regulatory process. One 42 year-old Las Vegas resident even filed a class-action lawsuit alleging that Nevada's medical marijuana registration program was unconstitutional for its excessive impedances and delays.
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The impedance of a particular antenna design can vary due to a number of factors that cannot always be clearly identified. This includes the transmitter frequency (as compared to the antenna's design or resonant frequency), the antenna's height above and quality of the ground, proximity to large metal structures, and variations in the exact size of the conductors used to construct the antenna. When an antenna and feed line do not have matching impedances, the transmitter sees an unexpected impedance, where it might not be able to produce its full power, and can even damage the transmitter in some cases.
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Half of such a `"T"` or `"Π"` section is (unsurprisingly) called a half-section. The image impedances of the half section are dissimilar on the input and output ports but are equal to the mid-series `ZiT` on the side presenting the series element and the mid-shunt `ZiΠ` on the side presenting the shunt element. A mid-series derived section (that is, a series m-type filter) has precisely the same image impedance, `ZiT`, as a k-type mid- series "`T`" filter. However, the image impedance of a half-section of such a filter (on the shunt side) is not the same and is designated `ZiΠm`.
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The difference between the non-inverting input voltage and the inverting input voltage is amplified by the op-amp. This connection forces the op-amp to adjust its output voltage simply equal to the input voltage (Vout follows Vin so the circuit is named op-amp voltage follower). The impedance of this circuit does not come from any change in voltage, but from the input and output impedances of the op-amp. The input impedance of the op-amp is very high (1 MΩ to 10 TΩ), meaning that the input of the op-amp does not load down the source and draws only minimal current from it.
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The revolving magnetic field produced with a two-phase system allowed electric motors to provide torque from zero motor speed, which was not possible with a single-phase induction motor (without an additional starting means). Induction motors designed for two-phase operation use a similar winding configuration as capacitor start single-phase motors. However, in a two-phase induction motor, the impedances of the two windings are identical. Two-phase circuits also have the advantage of constant combined power into an ideal load, whereas power in a single-phase circuit pulsates at twice the line frequency due to the zero crossings of voltage and current.
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Linear four-terminal circuits in which a signal is applied to one pair of terminals and an output is taken from another, are often modeled as two-port networks. These can be represented by simple equivalent circuits of impedances and dependent sources. To be analyzed as a two port network the currents applied to the circuit must satisfy the port condition: the current entering one terminal of a port must be equal to the current leaving the other terminal of the port. By linearizing a nonlinear circuit about its operating point, such a two-port representation can be made for transistors: see hybrid pi and h-parameter circuits.
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Figure 4: Current amplifier as a bilateral two-port network; feedback through dependent voltage source of gain β V/V Figure 3 and the associated discussion refers to a unilateral amplifier. In a more general case where the amplifier is represented by a two port, the input resistance of the amplifier depends on its load, and the output resistance on the source impedance. The loading factors in these cases must employ the true amplifier impedances including these bilateral effects. For example, taking the unilateral current amplifier of Figure 3, the corresponding bilateral two-port network is shown in Figure 4 based upon h-parameters.
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For a dim spot to occur, the shale has to have a lower acoustic impedance than both the water sand and the oil/gas sand, which is the opposite situation required for a bright spot to occur. This is possible because compaction causes the acoustic impedances of sands and shales to increase with age and depth but it does not happen uniformly – younger shales have a higher acoustic impedance than younger sands, but this reverses at depth, with older shales having a lower acoustic impedance than older sands.Brown, Alistar. R., (2010), “Dim Spots in Seismic Images as Hydrocarbon Indicators”, AAPG Search and Discovery Article #40514.
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Impedances, on the other hand, are deliberately not matched from output to input. The impedance of a line input is typically around . When driven by a line output's usual low impedance of 100 to 600 ohms, this forms a "bridging" connection in which most of the voltage generated by the source (the output) is dropped across the load (the input), and minimal current flows due to the load's relatively high impedance. Although line inputs have a high impedance compared to that of line outputs, they should not be confused with so-called "Hi-Z" inputs (Z being the symbol for impedance) which have an impedance of to over .
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This permits a loudspeaker to be used with an amplifier having a low internal impedance and a flat frequency response is realized for the combined amplifier/loudspeaker system. However, an amplifier with a low internal impedance delivers more electrical output power when the load impedance reduces (until the impedances become approximately matched). Such high power levels could cause damage to either the amplifier or the amplifier's power supply, or the circuit connected to the amplifier's output (including the loudspeaker). Therefore, an additional convention exists whereby loudspeaker manufacturers specify a conservative estimate of the average impedance that the loudspeaker will present while playing typical music.
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Independent analysis published in December 1950 proved that the revised Williamson amplifier remained prone to both infrasonic and ultrasonic oscillations. According to the analysis, infrasonic open-loop response of the Williamson amplifier is shaped by three high-pass filters: two interstage RC filters, each with a cutoff frequency of 6 Hz, and the output stage RL filter, formed by the valves' output impedances and the transformer's primary inductance. At zero input signal, the nonlinear RL filter has a cutoff frequency of 3 Hz. This combination of cutoff frequencies, wrapped inside a 2030dB frequency loop, is unstable. Williamson tried to suppress it with a compensation network, also serving as a smoothing filter.
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Signal terminators are designed to specifically match the characteristic impedances at both cable ends. For many systems, the terminator is a resistor, with a value chosen to match the characteristic impedance of the transmission line, and chosen to have acceptably low parasitic inductance and capacitance at the frequencies relevant to the system. Examples include 75-ohm resistors often used to terminate 75-ohm video transmission coaxial cables. Types of transmission line cables include balanced line such as ladder line, and twisted pairs (Cat-6 Ethernet, Parallel SCSI, ADSL, Landline Phone, XLR audio, USB, Firewire, Serial); and unbalanced lines such as coaxial cable (Radio antenna, CATV, 10BASE5 Ethernet).
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In power transmission systems and industrial power systems, often the short-circuit current is calculated from the nameplate impedances of connected equipment and the impedance of interconnecting wiring. For simple radial distribution systems with only a few elements, hand calculation is feasible, but computer software is generally used for more complex systems. Where rotating machines (generators and motors) are present in the system, the time-varying effect of their contribution to a short circuit may be evaluated. Stored energy in a generator may contribute much more current to a short circuit in the first few cycles than later on; this affects the interrupting rating selected for circuit breakers and fuses.
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The Miller theorem establishes that in a linear circuit, if there exists a branch with impedance Z, connecting two nodes with nodal voltages V1 and V2, we can replace this branch by two branches connecting the corresponding nodes to ground by impedances respectively Z/(1 − K) and KZ/(K − 1), where K = V2/V1. The Miller theorem may be proved by using the equivalent two-port network technique to replace the two-port to its equivalent and by applying the source absorption theorem. This version of the Miller theorem is based on Kirchhoff's voltage law; for that reason, it is named also Miller theorem for voltages.
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Every interaction over these interfaces comprised a 3-way handshake, which in the case of a processor accessing a memory module, consisted of send address, receive data, and send new data, a scheme well suited to the destructive read followed by rewrite required by magnetic-core memory of the time. These three phases were mediated by voltage edges rather than pulses, as this was thought to be faster. Furthermore, the input and output impedances of ECL were comparable to the characteristic impedance of ribbon cable. This, together with the small voltage swings between the "0" and "1" states made for low noise, reflection- free communication.
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Example of impedance and frequency scaling using a Π-section low- pass filter prototype. In the first transformation, the prototype is bisected and the cut-off frequency is rescaled from 1 rad/s to 105 rad/s (15.9 kHz). In the second transformation, the bisected network is rescaled on the left side to operate at 600 Ω and on the right side to operate at 50 Ω. There is an extension to Bartlett's theorem that allows a symmetrical filter network operating between equal input and output impedance terminations to be modified for unequal source and load impedances. This is an example of impedance scaling of a prototype filter.
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In telecommunications, a repeating coil is a voice-frequency transformer characterized by a closed magnetic core, a pair of identical balanced primary (line) windings, a pair of identical but not necessarily balanced secondary (drop) windings, and low transmission loss at voice frequencies. It permits transfer of voice currents from one winding to another by magnetic induction, matches line and drop impedances, and prevents direct conduction between the line and the drop. It is a special application of an isolation transformer, and is often used to prevent ground loops or earth loops, which cause humming or buzzing in audio circuits. It also prevents low direct current voltages from passing.
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Seismic waves are elastic waves that propagate through the Earth with a finite velocity, governed by the elastic properties of the rock in which they are travelling. At an interface between two rock types, with different acoustic impedances, the seismic energy is either refracted, reflected back towards the surface or attenuated by the medium. The reflected energy arrives at the surface and is recorded by geophones that are placed at a known distance away from the source of the waves. When a geophysicist views the recorded energy from the geophone, they know both the travel time and the distance between the source and the receiver, but not the distance down to the reflector.
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The cross section can then be calculated, using the diffraction coefficients, with the physical theory of diffraction or other high frequency method, combined with physical optics to include the contributions from illuminated smooth surfaces and Fock calculations to calculate creeping waves circling around any smooth shadowed parts. Optimization is in the reverse order. First one does high frequency calculations to optimize the shape and find the most important features, then small calculations to find the best surface impedances in the problem areas, then reflection calculations to design coatings. Large numerical calculations can run too slowly for numerical optimization or can distract workers from the physics, even when massive computing power is available.
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The audible aspect of this sort of electric hum is produced by amplifiers and loudspeakers. The other major source of hum in audio equipment is shared impedances; when a heavy current is flowing through a conductor (a ground trace) that a small-signal device is also connected to. All practical conductors will have a finite, if small, resistance, and the small resistance present means that devices using different points on the conductor as a ground reference will be at slightly different potentials. This hum is usually at the second harmonic of the power line frequency (100 Hz or 120 Hz), since the heavy ground currents are from AC to DC power supplies that rectify the mains waveform.
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8 Darlington's insertion-loss method is a generalisation of the procedure used by Norton. In Norton's filter it can be shown that each filter is equivalent to a separate filter unterminated at the common end. Darlington's method applies to the more straightforward and general case of a 2-port LC network terminated at both ends. The procedure consists of the following steps: #determine the poles of the prescribed insertion-loss function, #from that find the complex transmission function, #from that find the complex reflection coefficients at the terminating resistors, #find the driving point impedance from the short-circuit and open-circuit impedances, #expand the driving point impedance into an LC (usually ladder) network.
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Thus the design had to be revised because these new units had different impedances, technical characteristics and altered resonance patterns.[2][4] The tweeter was considered potentially fragile because it now had an exposed dome, so a suitable protection grille was found to cover and protect the dome. The tweeter was also surrounded by a thick felt rectangle to prevent interference pattern effects being created by the edge of the cabinet. The crossover also had to undergo change, and the LS3/5 became the LS3/5A in the early summer of 1974. The KEF B110 SP1003 is a 110mm speaker with a doped Bextrene (a proprietary type of polystyrene copolymer) cone and a neoprene surround.
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Graph theory has been used in the network analysis of linear, passive networks almost from the moment that Kirchhoff's laws were formulated. Gustav Kirchhoff himself, in 1847, used graphs as an abstract representation of a network in his loop analysis of resistive circuits.Kirchhoff, G. (1847) "Über die Auflösung der Gleichungen, auf welche man bei der Untersuchung der linearen Verteilung galvanischer Ströme geführt wird" (On the solution of the equations to which one is led during the investigation of the linear distribution of galvanic currents), Annalen der Physik und Chemie, 72 (12) : 497–508. This approach was later generalised to RLC circuits, replacing resistances with impedances. In 1873 James Clerk Maxwell provided the dual of this analysis with node analysis.
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Generally three conductors are required per AC 3-phase circuit, although single-phase and DC circuits are also carried on towers. Conductors may be arranged in one plane, or by use of several cross-arms may be arranged in a roughly symmetrical, triangulated pattern to balance the impedances of all three phases. If more than one circuit is required to be carried and the width of the line right-of-way does not permit multiple towers to be used, two or three circuits can be carried on the same tower using several levels of cross-arms. Often multiple circuits are the same voltage, but mixed voltages can be found on some structures.
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The two impedances form a voltage divider with a shunt element that is large relative to the size of the series element, which ensures that little of the signal is shunted to ground and that current requirements are minimized. Most of the voltage asserted by the output appears across the input impedance and almost none of the voltage is dropped across the output. The line input acts similarly to a high impedance voltmeter or oscilloscope input, measuring the voltage asserted by the output while drawing minimal current (and hence minimal power) from the source. The high impedance of the line in circuit does not load down the output of the source device.
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Modern solid state amplifiers, which use relatively high levels of negative feedback to control distortion, have extremely low output impedances—one of the many consequences of using feedback—and small changes in an already low value change overall damping factor by only a small, and therefore negligible, amount. Thus, high damping factor values do not, by themselves, say very much about the quality of a system; most modern amplifiers have them, but vary in quality nonetheless. Tube amplifiers typically have much lower feedback ratios, and in any case almost always have output transformers that limit how low the output impedance can be. Their lower damping factors are one of the reasons many audiophiles prefer tube amplifiers.
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In a sense this niche is a subset of OTLs however it merits treating separately because unlike an OTL for a loudspeaker, which has to push the extremes of a valve circuit's ability to deliver relatively high currents at low voltages into a low impedance load, some headphone types have impedances high enough for normal valve types to drive reasonably as OTLs, and in particular electrostatic loudspeakers and headphones which can be driven directly at hundreds of volts but minimal currents. Once more there are some safety issues associated with direct drive for electrostatic loudspeakers, which in extremis may use transmitting valves operating at over 1 kV. Such systems are potentially lethal.
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It should be born in mind that the characteristics of the filter predicted by the image method are only accurate if the section is terminated with its image impedance. This is usually not true of the sections at either end which are usually terminated with a fixed resistance. The further the section is from the end of the filter, the more accurate the prediction will become since the effects of the terminating impedances are masked by the intervening sections. It is usual to provide half half-sections at the ends of the filter with m = 0.6 as this value gives the flattest Z`i` in the passband and hence the best match in to a resistive termination.
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Although a preselector is placed in the same location as an antenna tuner, it serves a different purpose: An antenna tuner or “transmatch” connects two signal lines with different signal impedances and only blocks out-of-tune frequencies incidentally (if it blocks any at all). A transmatch matches transmitter impedance to feedline impedance, so that signal power from the radio transmitter smoothly transfers into the antenna’s feed cable; a properly adjusted transmatch prevents transmitted power from being reflected back into the transmitter (called ‘backlash current’). Some antenna tuner circuits can both impedance match and preselect, for example the Series Parallel Capacitor (SPC) tuner, and many circuits used in balanced line (BLT) tuners can be adjusted to also function as band-pass filters.
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In this case, actually working useful parameter is not the leakage inductance value but the short-circuit inductance value. Commercial and distribution transformers rated up to say 2,500 kVA are usually designed with short-circuit impedances of between about 3% and 6% and with a corresponding X/R ratio (winding reactance/winding resistance ratio) of between about 3 and 6, which defines the percent secondary voltage variation between no-load and full load. Thus for purely resistive loads, such transformers' full-to-no-load voltage regulation will be between about 1% and 2%. High leakage reactance transformers are used for some negative resistance applications, such as neon signs, where a voltage amplification (transformer action) is required as well as current limiting.
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Vereker also believed that a well- designed amplifier must be stable at all times when driving real-life loads, which are different from those achieved in lab conditions because loudspeakers' impedances vary with frequency. The inherent compromise between the pursuits for stability and sound quality means that Naim's power amplifiers are designed to work optimally with its own moderately priced speaker cable, and its predecessor . Product manuals warn users against using "high-definition wire or any other special cable between amplifier and loudspeaker". Whilst other manufacturers habitually employ Zobel networks (or an output filter which enhances amplifiers' stability) to protect against use with speakers and or cables with very high-capacitance, Naim amplifiers routinely omit these filters because of their adverse effect on sound quality.
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Launched in 1978 when the principal preoccupation of hi-fi manufacturers was power output, the sub-£80 (US$135) low-powered solid state amplifier, created and marketed by a then little-known manufacturer, gained a reputation for excellent sound quality and exceptional value. Stereophile magazine called the "ridiculously inexpensive". It was the first integrated amplifier built with convincing ability to drive difficult loudspeaker loads, and a sound quality that far exceeded other integrated amplifiers at its price point for the time. In an era when the NAD's rated power output of 20 watts per channel continuous into 8 ohms was considered anaemic, the manufacturer claimed it could deliver much stronger power output into lower impedances under dynamic conditions (music or peak power output).
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When reactive elements such as capacitors, inductors, or transmission lines are involved in a circuit to which AC or time-varying voltage or current is applied, the relationship between voltage and current becomes the solution to a differential equation, so Ohm's law (as defined above) does not directly apply since that form contains only resistances having value R, not complex impedances which may contain capacitance (C) or inductance (L). Equations for time-invariant AC circuits take the same form as Ohm's law. However, the variables are generalized to complex numbers and the current and voltage waveforms are complex exponentials. In this approach, a voltage or current waveform takes the form Ae, where t is time, s is a complex parameter, and A is a complex scalar.
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An isolated generator may be specially designed to ensure that it can source enough current on a short circuit to allow subordinate overcurrent protection devices to operate properly. Where an industrial system is fed from an electrical utility, the short circuit level at the point of connection may be specified, often with minimum and maximum values or values to be expected after system growth. This allows calculation by an industrial customer of its internal fault levels within its plant. If the prospective short-circuit current from the utility source is very large compared to the customer's system size, an "infinite bus" is assumed, with zero effective internal impedance; the only limit to the prospective short- circuit current is then the impedances after the defined "infinite bus".
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It is however, relatively easy these days to design an audio amplifier with any of a range of output impedances, even down to nearly zero. In a hypothetical situation with an amplifier having an output impedance much higher than zero, say 8Ω, then it is true that maximum power will be delivered if the loudspeaker also has an 8Ω impedance. This is assuming that the amplifier is modeled by VS and ZS as shown above, and that the VS between the two example amplifiers have the same value. The matched impedance situation is encountered much more in non-audio-related situations, for example in antenna design where the impedance at the antenna terminals takes on a set value due to requirements in its geometry.
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In circuit design, an active load is a circuit component made up of active devices, such as transistors, intended to present a high small-signal impedance yet not requiring a large DC voltage drop, as would occur if a large resistor were used instead. Such large AC load impedances may be desirable, for example, to increase the AC gain of some types of amplifier. Most commonly the active load is the output part of a current mirror and is represented in an idealized manner as a current source. Usually, it is only a constant-current resistor that is a part of the whole current source including a constant voltage source as well (the power supply VCC on the figures below).
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Only when all 3 input signals are 0 (low voltage) do the emitter-collector impedances of all 3 transistors remain very high. Then very little current flows, and the voltage- divider effect with the load impedance imposes on the collector point a high voltage very near to Vcc. The complementing property of these gate circuits may seem like a drawback when trying to implement a function in canonical form, but there is a compensating bonus: such a gate with only one input implements the complementing function, which is required frequently in digital logic. This example assumes the Apollo parts inventory: 3-input NOR gates only, but the discussion is simplified by supposing that 4-input NOR gates are also available (in Apollo, those were compounded out of pairs of 3-input NORs).
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Different make and model headphones have widely varying impedances, from as little as to a few hundred ohms; the lowest of these will have results similar to a speaker, while the highest may work acceptably if the line out impedance is low enough and the headphones are sensitive enough. Conversely, a headphone output generally has a source impedance of only a few ohms (to provide a bridging connection with 32 ohm headphones) and will easily drive a line input. For similar reasons, "wye"-cables (or "Y-splitters") should not be used to combine two line out signals into a single line in. Each line output would be driving the other line output as well as the intended input, again resulting in a much heavier load than designed for.
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An American T-12 Cloudmaker seismic bomb An explosion in air does not transfer much energy into a solid, as their differing acoustic impedances makes an impedance mismatch that reflects most of the energy. Due to the lack of accuracy of bombing in the face of anti-aircraft defences, air forces used area bombardment, dropping large numbers of bombs so that it would be likely that the target would be hit. Although a direct hit from a light bomb would destroy an unprotected target, it was comparatively easy to armour ground targets with many yards of concrete, and thus render critical installations such as bunkers essentially bombproof. If the bomb could be designed to explode in water, soil, or other less compressible materials, the explosive force would be transmitted more efficiently to the target.
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Seismic waves are mechanical perturbations that travel in the Earth at a speed governed by the acoustic impedance of the medium in which they are travelling. The acoustic (or seismic) impedance, Z, is defined by the equation: :Z=V\rho \ , where V is the seismic wave velocity and ρ (Greek rho) is the density of the rock. When a seismic wave travelling through the Earth encounters an interface between two materials with different acoustic impedances, some of the wave energy will reflect off the interface and some will refract through the interface. At its most basic, the seismic reflection technique consists of generating seismic waves and measuring the time taken for the waves to travel from the source, reflect off an interface and be detected by an array of receivers (or geophones) at the surface.
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The impedance of the meter varies depending on the basic sensitivity of the meter movement and the range which is selected. For example, a meter with a typical 20,000 Ω/V sensitivity will have an input resistance of 2 MΩ on the 100 V range (100 V × 20,000 Ω/V = 2,000,000 Ω). On every range, at full-scale voltage of the range, the full current required to deflect the meter movement is taken from the circuit under test. Lower sensitivity meter movements are acceptable for testing in circuits where source impedances are low compared to the meter impedance, for example, power circuits; these meters are more rugged mechanically. Some measurements in signal circuits require higher sensitivity movements so as not to load the circuit under test with the meter impedance.
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By expanding a one-line diagram to show the positive sequence, negative sequence, and zero sequence impedances of generators, transformers and other devices including overhead lines and cables, analysis of such unbalanced conditions as a single line to ground short-circuit fault is greatly simplified. The technique can also be extended to higher order phase systems. Physically, in a three phase system, a positive sequence set of currents produces a normal rotating field, a negative sequence set produces a field with the opposite rotation, and the zero sequence set produces a field that oscillates but does not rotate between phase windings. Since these effects can be detected physically with sequence filters, the mathematical tool became the basis for the design of protective relays, which used negative-sequence voltages and currents as a reliable indicator of fault conditions.
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The best coaxial cable impedances in high-power, high-voltage, and low-attenuation applications were experimentally determined at Bell Laboratories in 1929 to be 30, 60, and 77 Ω, respectively. For a coaxial cable with air dielectric and a shield of a given inner diameter, the attenuation is minimized by choosing the diameter of the inner conductor to give a characteristic impedance of 76.7 Ω. When more common dielectrics are considered, the best-loss impedance drops down to a value between 52–64 Ω. Maximum power handling is achieved at 30 Ω. The approximate impedance required to match a centre-fed dipole antenna in free space (i.e., a dipole without ground reflections) is 73 Ω, so 75 Ω coax was commonly used for connecting shortwave antennas to receivers. These typically involve such low levels of RF power that power-handling and high-voltage breakdown characteristics are unimportant when compared to attenuation.
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The line impedance must be matched to the impedance of the antenna at one end and the transmitter at the other to efficiently transfer power between the transmitter and its antenna. If the impedances at either end of the line do not match, it will cause a condition called "standing waves" on the feed line, in which the RF energy is reflected back toward the transmitter, wasting energy and possibly overheating the transmitter. The impedance is matched through a device called an antenna tuner or matching network, which can be in the transmitter, next to the transmitter, near the antenna, on the antenna, or any combination, including none. The degree of mismatch between the feedline and the antenna is measured by an instrument called an SWR meter (standing wave ratio meter), which measures the standing wave ratio (SWR) on the line: The ratio of the adjacent maximum and minimum voltage amplitudes, or adjacent maximum and minimum current amplitudes.
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Realistic STA-240 receiver Back of unit showing connections The TRM-800 was a Hi-End solid state integrated stereo amplifier made in Japan, using NEC power transistors, by Nikko. It was the top of the line model in the Nikko amplifier range of TRM's series; beautifully housed in a wooden walnut- finished cabinet and a handsome brushed aluminum front panel, was introduced in 1975hifiengine.com 2020, Nikko TRM-800 retrieved 29 June 2020. the same year as the Marantz 2235.hifiengine.com 2020, Marantz 2235, retrieved 29 June 2020.High Fidelity magazin August 1975, retrieved 29 June 2020 (scan at angelfire.com). It was a 2 channel amp; however, it had three sets of speaker connections; those powered selected by buttons. At 8 ohms, the amp could put out 65 Watts per channel RMS (90 Watts per channel RMS at 4 ohms), delivering superb high fidelity sound with exceptional tone quality. Unlike many amps of this time, however, the TRM-800 was stable at lower impedances than 8 ohms; down to 4 ohms.
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If there is still a high standing wave ratio (SWR) in the feedline beyond the ATU, any loss in that part of the feedline is typically increased by the transmitted waves reflecting back and forth between the tuner and the antenna, causing resistive losses in the wires and possibly the insulation of the transmission line. Even with a matching unit at both ends of the feedline - the near ATU matching the transmitter to the feedline and the remote ATU matching the feedline to the antenna - losses in the circuitry of the two ATUs will slightly reduce power delivered to the antenna. # The most efficient use of a transmitter's power is to use a resonant antenna, fed with a matched-impedance feedline; there are still small losses in any feedline even when all impedances match, but matching minimizes loss. # It is almost as efficient to feed a remote antenna tuner attached directly to the antenna, via a feedline matched to the transmitter and the ATU feed; the only extra losses are in the tuner circuitry, which can be kept small if the tuner is correctly adjusted and the line carefully tested at or near the antenna.
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Simplified diagram (omitting grid bias network) The electrical bridge of a circlotron is formed by a matched pair of triodes (V1, V2) and two floating power supplies ('B batteries'), B1+ and B2+. Grids of each triode are driven in opposite phases with a balanced, symmetrical input signal; differential current flows through the loudspeaker load and a simple, relatively high impedance, resistor network that ties floating supplies to the ground. Tubes are usually fixed biased with an external negative power supply ('C battery'); each side normally has independent bias adjustment to compensate for minor tube mismatch. Output impedance Z of a transformerless circlotron where each stage is a single triode with plate impedance of Rp and voltage gain of μ is defined by the formula :Z = R_p / (2 + \mu)See a comparison of OTL topologies and their output impedances Tube Lovers Anonymous The tubes best fitting the circlotron concept are triodes designed for use in power supplies as series regulators: 6080/6AS7, 6C33C, 6C19P. An amplifier with one 6AS7 dual triode per channel (Rp = 270 ohms,Actual Rp in a paralleled setting may be even higher due to conservative biasing μ = 2) will have a Z of about 67 ohms—sufficient to drive most headphones.
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