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Electrical Engineers, Proceedings of the Institution of

Issue 1 • Date January 1967

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Displaying Results 1 - 25 of 30
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  • Translating and transcoding between colour-television systems with common scanning standards

    Page(s): 23 - 29
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1020 KB)  

    The problems associated with the international exchange of colour-television programmes are discussed. The interchange of programmes between Europe and America would be possible, without conversion between the scanning standards, if dual standards were adopted in Europe, and an experiment is described in which the feasibility of dual-standard colour television is assessed from the point of view of the subcarrier frequency-changing or translating process. It now seems certain that different colour systems, operating on a common 625-line scanning standard, will be used within Europe, and investigations have been carried out into methods of transcoding between the proposed systems. These investigations show that both translating and transcoding operations between one colour system and another on the same scanning standard can be accomplished without serious impairment of the picture quality. View full abstract»

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  • Reradiation from masts and similar obstacles at radio frequencies

    Page(s): 30 - 42
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1666 KB)  

    Transmissions from v.h.f. and u.h.f. aerials may be distorted by reradiated signals if tall obstacles such as masts or towers are situated in the service area. The amplitudes of these reradiated signals are governed by factors discussed in the paper. View full abstract»

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  • On complex waves

    Page(s): 43 - 49
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (912 KB)  

    A widely used approximate technique for treating radiation problems involving a source-excited interface is derived from a saddle-point evaluation of the inverse transform-integral representation of the solution. The total solution is approximated to by the first saddle-point term plus residue terms in their respective wedges of contribution, i.e. space wave plus complex waves. The paper considers the well known approximation of space wave plus complex waves in the light of the modified saddle-point technique. The condition for validity of this approximation is shown to be that the numerical distance, a quantity involving both the distance from pole to saddle point and the distance from origin to observation point, should be greater in magnitude than ten. The discussion is numerically illustrated using the example of unidirectional travelling-leaky-wave and surface-wave aperture distributions. For these examples, graphs are compared of the approximate solutions and of solutions including the correction terms. Diagrams which show where in space the complex wave is a valid and significant part of the total solution are also constructed. The leaky-wave case is particularly interesting, since the correction terms are required in a rather large region of space. View full abstract»

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  • Generalised high-frequency network theory of field-effect transistors

    Page(s): 50 - 59
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1114 KB)  

    The paper is concerned with calculation of the small-signal admittance parameters of field-effect transistors in general. For this purpose, it is first shown that field-effect transistors can be effectively treated as a special class of analogue RC transmission lines, in which the resistance is uniformly distributed but the capacitance is nonuniformly distributed. The difficulty of analysing this type of transmission line is resolved by assuming piecewise uniformity as a good first-order approximation. The matrix method of analysis is employed. This has been found to be a simple and rapid means of calculating admittance parameters of field-effect transistors in a closed analytical form, which is particularly suitable for practical circuit analyses. These parameters lead naturally to the appropriate representation of device characteristics by equivalent circuits, valid over their entire useful frequency range. Calculation of both the forward- and reverse-transmission parameters under saturated-drain-current conditions has been the main object of the analysis, which is, however, in general terms throughout. View full abstract»

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  • Effects of amplifier imperfections in a particular RC-active circuit

    Page(s): 60 - 70
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1143 KB)  

    The performance of a particular RC-active circuit, using a modified parallel T with unity-gain amplifier, is analysed on the assumption that the amplifier is ideal. Approximate expressions are then derived which enable the effects of finite input impedance, nonzero output impedance and nonzero source impedance to be calculated. It is shown that some of these effects can be reduced in magnitude by the use of an infinite-gain, instead of a unity-gain, amplifier, and that a further improvement is possible by using the two types of amplifier together in one circuit. The analysis is extended to cover these two arrangements. View full abstract»

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  • Stability of passive time-variable circuits

    Page(s): 71 - 75
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (566 KB)  

    Lyapunov's second method is used to show that circuits composed of a finite connection of linear, passive, time-variable elements are necessarily stable. Such connections may involve transformers and gyrators as circuit elements, as well as the conventional resistors, inductors and capacitors. An equivalent structure is determined, using only time-variable gyrators to interconnect constant elements consisting of unit capacitors and unit resistors. Using this model, asymptotic stability and uniform asymptotic stability of the original circuit may be investigated. Examples are given to illustrate the methods and concepts. View full abstract»

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  • Pathfinding through a communication network

    Page(s): 76 - 78
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (345 KB)  

    A technique is proposed by which all paths of exactly q branches interconnecting a given source-sink node pair can be obtained. Using the proposed technique, paths of increasing length can be found sequentially. The method is based on a symbolic noncommutative multiplication among the entries of an Nmatrix which is a modified version of the vertex adjacency matrix. View full abstract»

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  • Design of tapped-potentiometer function generators

    Page(s): 79 - 85
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (876 KB)  

    A simple method is described for the design of tapped-potentiometer circuits to produce an output voltage which is any specified function of the shaft rotation. Functions of any complexity may be synthetised, the circuits requiring only one source of e.m.f. The design procedure may be carried out on a digital computer or alternatively a simple graphical method is presented. View full abstract»

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  • High-speed 3-phase thyristor convertor with several unusual features

    Page(s): 102 - 108
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    The paper describes a 3-phase thyristor convertor with good input/output-voltage linearity and compensation for mains fluctuations. A form of electronic protection is used which safeguards the controller from faults, yet allows a margin of overcurrent capability. The firing circuit of the controller consists of tristable transistor circuits which appear to be especially suited to driving a 3-phase system of thyristors. Details of performance are given. View full abstract»

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  • Steady-state thermal analysis of a 400 kV-cable through joint

    Page(s): 109 - 115
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    Temperature distributions in a 400kV through joint and associated cable, as used in directly buried transmission circuits, are obtained for natural cooling and various forms of artificial cooling. The joint, rather than the cable, is seen to limit the current rating for all forms of cooling. With the higher ratings resulting from artificial cooling, the joint limitation becomes more severe. In all the cases considered, including the use of water jackets around the glass-fibre box surrounding the joint, the conductor temperature at the centre of the joint is above 85°C when the rating is decided by the cable alone. A thermal resistivity of the soil of 120degCcm/W, and a maximum coolant-temperature rise of 20degC are assumed. Investigation into joint power factors in the. range 0.004¿0.008 shows a large temperature dependence with natural cooling, but small dependence with artificial cooling. View full abstract»

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  • Performance of suboptimal linear control systems

    Page(s): 124 - 128
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (593 KB)  

    It is shown that the calculation of the performance of a class of suboptimal linear control systems is similar to the calculation of the performance of an equivalent optimal system. The performances of both optimal and suboptimal linear systems have terms for cost owing to uncertainty about the initial state of the plant, a nonzero mean of the initial state, error in the estimate of the state, and error in control owing to additive noise at the input. A suboptimal system, in addition to having greater costs than the optimal system for each of these terms, has a cost term which vanishes if either optimal control or optimal estimation is used. View full abstract»

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  • Dynamic analysis of nonlinear control systems

    Page(s): 129 - 138
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1022 KB)  

    A method of transient analysis which applies to autonomous and nonautonomous nonlinear systems of any order or configuration is presented. After noting that the transients which occur in such systems may be represented by an exponentially damped sinewave with time-varying damping and frequency, it is shown, by assuming the damping and frequency to be piecewise constant, that the nonlinearity in the system may be adequately characterised by an equivalent gain for transient phenomena. The equation governing the damping and frequency is then derived and shown to be nonlinear. An approximate solution of this equation is obtained, and a method is then developed for calculating the error in the approximation. Application of the theory to a bang-bang position-control system and a position-control system with resetter backlash illustrates the technique for systems with single-valued and phase-shifting nonlinearities. It is shown that the accuracy of prediction is similar to that obtained when the describing-function technique is used to predict limit cycles. Finally the results from this method are compared with those based on the describing-function characterisation, and it is found that appreciable improvement in the accuracy of prediction is obtained. View full abstract»

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  • Ripple instability in closed-loop control systems with thyristor amplifiers

    Page(s): 139 - 152
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    In a simplified analysis of thyristor amplifiers in closed-loop control systems, the amplifier is represented at all frequencies by its d.c. gain, and the effect of the output ripple voltage is neglected. This approach is inadequate for wide-bandwidth systems, and fails to predict the occurrence of ripple instability. A more accurate analysis is made in the paper, taking into account the sampling action of the amplifier in the presence of alternating component voltages in the loop. Ripple instability is characterised by the generation of continuous oscillations at a subharmonic of the balanced-amplifier ripple frequency, and manifests itself in the amplifier as a periodic variation in the firing pattern. The behaviour of an m-phase amplifier in an otherwise linear system of any order is investigated, and an exact analysis is given for subharmortic oscillations of order ¿. At the ¿-order, and other, subharmonic frequencies, describing functions are derived, and the amplifier response is seen to differ markedly from the simple assumption of constant gain at all frequencies. The describing-function technique is extended to evaluate phase margins which must be satisfied at the various subharmonic frequencies to prevent ripple instability, thus allowing a straightforward design technique based on conventional frequency-response methods. The results of the analysis are compared with experimental results from regulated power-supply systems, and good agreement is reached. View full abstract»

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  • Note on Whiteley's a.c. compensating network

    Page(s): 153 - 155
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (212 KB)  

    Whiteley's demodulating compensating network for use in a.c. servomechanisms is analysed in a phase-lag mode of operation. The transfer function is derived, and the notch frequency is shown to be related to the reference carrier frequency. The criterion that (¿sT)2 ¿ 1 must be satisfied is discussed. View full abstract»

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  • Contrast-transfer characteristics of n tuple models of retinal receptive fields

    Page(s): 156 - 160
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    Contrast-transfer characteristics based on a simplified model of a retinal receptive field using a very limited number of receptors are described. The model is linear for given luminance levels. Of the many possible methods of switching these models, the one chosen uniformly changes the weighting coefficients associated with all receptors and is expressed as a change in static-transfer coefficient. Contrast-transfer characteristics are given as a function of optical-signal size (or spatial frequency) for various binary patterns. These characteristics may be used to select a compromise condition between the static- and contrast-transfer requirements of a pattern preprocessor, which in turn is a compromise between detectability and processing fidelity of signals. View full abstract»

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  • Automatic focusing of an optical system by extremum control

    Page(s): 161 - 165
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (645 KB)  

    A method is described for automatically focusing a high-power optical microscope using an extremum controller. The principle used is that of maximising the amplitudes of certain high-frequency components of a signal derived by scanning the object. The optimum bandpass filter required in selecting these frequency components is derived on the basis of expected power spectra, and the reasons for deviating, somewhat from this optimum are explained on the basis of the statistical variations in harmonic amplitudes of practical objects. A practicable system employing a peak-holding controller is described, in which the average hunting excursion about focus is less than the normally accepted depth of focus of the optical system. View full abstract»

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Aims & Scope

The Proceedings of the Institution of Electrical Engineers was published by the IET between 1963 and 1979.

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