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Electrical Engineers, Proceedings of the Institution of

Issue 8 • Date August 1969

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Displaying Results 1 - 25 of 30
  • Measurements on aircraft echoes using wideband pulse-compression radar

    Publication Year: 1969 , Page(s): 1293 - 1296
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (613 KB)  

    This paper describes measurements designed to study the effect of very short pulses on aircraft echoes. A method is described for making simultaneous comparative echoing-area measurements on aircraft in flight, for different pulse durations. Experimental results indicate a reduction in echoing area as the resolution cell becomes small compared with the aircraft dimensions. Photographs of high-resolution video responses are given for three types of aircraft. Separate radar returns from different parts of the airframe can be clearly distinguished. View full abstract»

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  • Propagation effects and lane-ambiguity resolution in OMEGA

    Publication Year: 1969 , Page(s): 1297 - 1303
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (844 KB)  

    Experimental data on v.l.f. propagation taken during aircraft flights from the United Kingdom over the North Atlantic have shown that, at night, waveguide-mode interference is appreciable at distances of at least 7000km from the transmitter, for frequencies between 10 and 14kHz. The implications of these propagation results on the lane-resolution ability of the OMEGA v.l.f. navigational aid is discussed. View full abstract»

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  • Ultimate communications capacity of the geostationary-satellite orbit

    Publication Year: 1969 , Page(s): 1304 - 1310
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1000 KB)  

    The geostationary-satellite orbit is uniquely useful for communication satellites. There is, however, an ultimate limit to the number of communications channels which the orbit can support in a given bandwidth owing to the effects of interference between adjacent satellites. By calculating the minimum separation angles between satellites, the capacity of a 10° arc of orbit and a 500 MHz bandwidth is determined as a function of earth-station-aerial diameter and satellite-transmitter power. Results are given for frequency modulation and pulse-code modulation for telephony, and for frequency modulation only for television. The effect on the results of variations in some of the basic assumptions made are discussed in some detail. These include the interference noise permitted, the interleaving of channel carrier frequencies, the use of narrow-beam satellite aerials, and the use of frequency bands higher than those at 4GHz and 6GHz which are used at present. It is shown that capacities of 2000 telephone circuits per degree of orbit might be expected using earth-station aerials 20¿30m in diameter. It is further concluded that one of the most significant ways to increase the efficient use of a given arc of orbit is to carefully co-ordinate the characteristics and methods of operation of systems using adjacent satellites. View full abstract»

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  • Selection of intermodulation-free frequencies for multiple-channel mobile radio systems

    Publication Year: 1969 , Page(s): 1311 - 1318
    Cited by:  Papers (9)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (798 KB)  

    The paper presents results which enable the designer of a mobile radio network to allocate channel frequencies which give freedom from interfering third- or fifth-order intermodulation products. The general rules for the selection of third- and fifth-order mutually compatible channels are developed, and Tables of channel-difference sequences are presented for direct use in channel allocation. An extension of the theory for immunity to higher-order products is also given. View full abstract»

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  • WISDOM: a method of synchronising distributed stations to a p.c.m. system

    Publication Year: 1969 , Page(s): 1319 - 1324
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (634 KB)  

    The principles of a method of random access for distributed static stations to a synchronised pulse-code-modulation multiplex system has been described. This paper explains the instrumentation used to build a model to demonstrate the automatic switching of stations to operate in a free channel, and the cross-connection required to apply a store-and-forward technique to pulse-coded signals. The system, which is adapted from one designed for operation with mobile outstations, has a number of limitations. These are considered, and an indication given of the solutions adopted to overcome them in a new demonstration model. The name WISDOM has been derived from `Wing's self-synchronising delayed-delta orthogonal-channel modulator¿. View full abstract»

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  • Methods for shaping vertical radiation patterns of v.h.f. and u.h.f. transmitting aerials

    Publication Year: 1969 , Page(s): 1325 - 1337
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1637 KB)  

    An important problem in the design of v.h.f. and u.h.f. transmitting aerials is the provision of a vertical radiation pattern, which gives an approximately uniform field strength over the prescribed service area. A good solution is provided by a beam-tilted cosecant-shaped radiation pattern. Several methods are described for synthetising radiation patterns of this type by varying either the amplitudes or the phases (or both) of the radiating currents in a linear column of equispaced elements. Some examples are given of the application of these techniques to the types of multitiered aerials employed at v.h.f. and u.h.f. broadcasting stations. Consideration is also given to the problems of realising the required current distributions, and important design factors such as aerial-impedance matching and pattern bandwidth are discussed. Recommendations are made for selecting v.r.p.-shaping techniques to satisfy a range of design requirements. View full abstract»

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  • Gramophone-record reproduction: development, performance and potential of the stereophonic pickup

    Publication Year: 1969 , Page(s): 1338 - 1344
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1151 KB)  

    This paper describes the development of the stereophonic gramophone pickup since 1958. The basic requirements for such a pickup are given. The characteristics of the early pickups and improvements over the past ten years are discussed. Emphasis is placed on tracing and tracking distortion, mistracking and frequency response. The paper concludes with a list of problems which must still be resolved. View full abstract»

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  • Analysis of transistor second breakdown

    Publication Year: 1969 , Page(s): 1345 - 1348
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (369 KB)  

    The phenomenon of second breakdown in transistors is analysed when the breakdown process is initiated by a thermal mechanism. An expression is developed relating the characteristic delay time to the power dissipated in the collector junction. For short delay times, a simple relationship is shown to exist between the parameters describing the breakdown. Experimental results are presented which indicate a reasonable correlation with the theoretical predictions. View full abstract»

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  • Transient response of networks employed in protective relaying

    Publication Year: 1969 , Page(s): 1349 - 1355
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (695 KB)  

    Series and parallel combinations of resistance and inductance are investigated theoretically under maximum-transient conditions, to find alternative representations of the replica impedance employed in distance-protection applications for which the line current is converted to an equivalent voltage. When the primary-system-impedance angle exceeds the replica-impedance angle, the parallel configuration is shown to develop a significantly reduced transient component of the output voltage, and a lower transient flux is required in the core of the energising current transformer. The parallel-tuned-filter circuit is employed in differential current-protection schemes to allow a reduction in the transient component of the relaying quantity derived via a current transformer. The circuit parameters are investigated with a view to minimising the transient-flux requirements of the current transformer and developing an output approaching proportionality with the a.c. component of the primary current. The treatment includes energisation at nonresonant frequencies. View full abstract»

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  • Theoretical aspects of thermomechanical forces in power cables

    Publication Year: 1969 , Page(s): 1356 - 1360
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (518 KB)  

    A theoretical treatment of the mechanical forces developed in power cable conductors as a result of temperature changes is presented, using equations based upon classical beam theory. From considerations of flexural rigidity, it is shown that, in most practical cases, such conductors should have very little bending stiffness and possess considerable longitudinal stiffness. It is also proposed that a joint may be effectively represented as a very stiff spring. For single-core cables, the theory is in good agreement with previously published work, under most practical conditions. A brief extension of the analysis to cover the mechanical behaviour of multicore cables is given. View full abstract»

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  • Rating of bare overhead conductors for intermittent and cyclic currents

    Publication Year: 1969 , Page(s): 1361 - 1376
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1550 KB)  

    Equations are derived and solutions given for determining the variation with time of the temperature of bare overhead conductors carrying intermittent and cyclic currents. The temperature variation depends on the rate of heat input, the heat capacity of the conductor and the rate of total heat transfer. The latter is proportional to (temperature rise)q. If the heat transfer by radiation can be neglected, q=1 for forced convection and approximately 1.25 for natural convection. If radiation is not negligible, q is greater than 1, the actual value being obtained from calculations or steady-state measurements. Thermal time constants can only be used when q=1, and they are then only approximations. Measured heating- and cooling-time constants agree reasonably well with calculated values. The significance of the difference between heating- and cooling-time constants is discussed. The importance of the heat source or sink formed by the core in steel-cored conductors is shown, and calculated values of the radial thermal conductivity are similar to those found from previous steady-state measurements. Calculated temperature/time characteristics for conductors in still air are in good agreement with measured characteristics. View full abstract»

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  • Insulation for high-voltage a.c. railway electrification in Great Britain

    Publication Year: 1969 , Page(s): 1377 - 1386
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1530 KB)  

    The paper traces the development of ceramic and synthetic insulators used on the high-voltage a.c. electrification schemes of British Railways (BR). Details are given of operating experience and the factors which led to each successive development. Most of the earlier difficulties were due to severe pollution from steam locomotives, and the paper describes the measures taken to overcome these difficulties, and also the innovations which are now possible owing to the cessation of steam traffic. Another important aspect of insulation is the air clearance required, since this has a great effect on the extent and expense of civil-engineering work. The paper details the original requirements for air clearances and arrangement of the overhead equipment at bridges and tunnels, and also the present reduced requirements and the tests which led to their adoption. View full abstract»

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  • Ignition phenomena in h.v. mercury-arc valves

    Publication Year: 1969 , Page(s): 1387 - 1394
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1095 KB)  

    A streamer mechanism is proposed to explain the ignition phenomena which are observed in multigrid high-voltage gas-filled valves. Theoretical treatment of the streamer shows it to propagate at higher velocity with increasing gas pressure and decreasing valve voltage, in accordance with observation. Some of the conditions necessary for normal reliable ignition are related theoretically to the avoidance of transient cutoff of the streamer. View full abstract»

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  • Saturated leakage reactances of cage induction motors

    Publication Year: 1969 , Page(s): 1395 - 1404
    Cited by:  Papers (6)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1200 KB)  

    The paper presents a method of predicting the saturation of the leakage reactances of cage induction motors. It commences with a discussion of leakage fluxes and reactances and the manner in which they are affected by magnetic saturation. The calculation of the components of leakage reactance under unsaturated conditions is described. The theory then progresses to the calculation of the magnitude and phase of the leakage-flux components likely to be affected by saturation, and to the determination of the leakage-flux paths. A general method is given for computing reduction factors, or saturation factors, to be applied to those components of leakage reactance with saturable associated fluxes. A logical system for dealing with complex magnetic circuits which contain combinations of fluxes in a number of saturable areas is described and explained by the use of examples. Saturable areas in the magnetic circuits of induction motors are defined for a number of alternative slot shapes. The variation of skew-leakage flux, and therefore of the saturation, as a function of axial position is treated by subdividing the core length into short sections and summing their reactances. Results of computations are compared with test results on 18 medium and large motors, and good correlations are shown for both unsaturated and saturated locked-rotor impedances. View full abstract»

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  • Performance and design of induction motors with square-wave excitation

    Publication Year: 1969 , Page(s): 1405 - 1411
    Cited by:  Papers (12)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (864 KB)  

    The paper investigates the reasons for loss of efficiency when conventional induction motors are supplied with square-wave voltages. A method of analysis using harmonic travelling current-density waves is developed and methods of design are described to produce induction motors with comparable efficiency and output to those of sinusoidally fed machines. The air-gap flux densities in these motors are discussed, and experimental values of iron losses are given to compare with conventional machines. View full abstract»

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  • Induction-excited alternator

    Publication Year: 1969 , Page(s): 1412 - 1418
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (901 KB)  

    The paper describes a new form of alternator excitation. No sliding contacts are used and no rectifiers rotating on the shaft are required. The rotor consists of N equally spaced rotor windings in which approximations to a square wave of current are induced. Over sections of the machine, when the rotor coils are carrying substantially constant current, the output windings behave like sections of a d.c.-excited alternator with 2N poles. Two experimental machines are described and a comparison is made between the induction-excited alternator and (a) a d.c.-excited alternator and (b) an inductor alternator. View full abstract»

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  • Methods of measurement of acoustic noise radiated by an electric machine

    Publication Year: 1969 , Page(s): 1419 - 1431
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1459 KB)  

    The acoustic field of an electric machine is described, and the basic measuring techniques and instrumentation for measuring noise are described. The results of sound-pressure measurements in free-field and semireverberant-field conditions, and measurements of sound pressure above a reflecting plane with various shapes of measuring surface are presented and discussed. From these measurements, the total sound power is calculated. The errors involved in using different numbers of sound-pressure sampling points in the power calculation, and of using approximate calculating procedures, are also investigated. Evidence is presented concerning the accuracy of methods of measurement and calculation. View full abstract»

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  • Generalisation of the equal-area criterion for synchronous machines

    Publication Year: 1969 , Page(s): 1431 - 1432
    Cited by:  Papers (1)
    Save to Project icon | PDF file iconPDF (160 KB)  
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  • Stability and control of distributed-parameter systems

    Publication Year: 1969 , Page(s): 1433 - 1438
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (605 KB)  

    A system described by a set of partial differential equations is considered, and control laws are generated so that a quadratic performance index takes on smaller values for the controlled system than the uncontrolled system. The controls are suboptimal, and are obtained from a linear system of partial differential equations. Both domain and boundary controls are considered, and the asymptotic stability of the controlled system is examined. The methods are applied to examples in which explicit results are obtained and comparisons made with the optimal controls. View full abstract»

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  • Analytical results on the use of reduced models in the control of linear dynamical systems

    Publication Year: 1969 , Page(s): 1439 - 1444
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    Two sets of first-order differential equations denoted by X and Xr are assumed to exist, where X and Xr govern the behaviour of the plant and the reduced model, respectively. The performance of the plant when it is controlled on the false assumption that its behaviour is governed by Xr is investigated. There optimal-control problems are considered: (a) fixed-target fixed-terminal-point minimum-energy problem (b) fixed-target free-terminal-point minimum-energy tracking problem (c) output-regulation problem. Explicit relations are obtained for the deterioration in performance in model control of the plant. In the first two problems, the interconnection between the error functional commonly adopted for the model-reduction problem and the deterioration in performance is demonstrated; the results are applied to reduced models obtained by the method of optimal projection along invariant subspaces. View full abstract»

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  • Method of closed-loop digital control

    Publication Year: 1969 , Page(s): 1445 - 1448
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (612 KB)  

    Between large complex digital-computer control systems and simple analogue process-control loops lies an area in which relatively simple digital electronic controllers are needed. The device described in the paper consists of a pulse-repetition-rate sensing device, a controller working on mathematical principles (which are analysed in some detail in the paper) and an output device which converts the correction signal into pneumatic form for use with conventional pneumatic positioning-control valves. The results of laboratory tests are also reported, and the unit is now undergoing field trials and further development. View full abstract»

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  • Use of power and energy concepts in the analysis of multivariable feedback controllers

    Publication Year: 1969 , Page(s): 1449 - 1452
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (487 KB)  

    The general linear-feedback multivariable-regulator problem is considered in terms of the injection of power into the controlled system by the controller. The concepts of power, energy, power decomposition, active power and reactive power are studied in this context and shown to give a physical insight into the techniques of modal control and spin-space mapping. An analogy is established between the energy exchanges of a system and its controller, and the energy-interchange effects in quantum mechanics. View full abstract»

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  • Dual-system methods in dynamical analysis. Part 1: Variational principles and their application to nonlinear-network theory

    Publication Year: 1969 , Page(s): 1453 - 1457
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (439 KB)  

    The feedback connection of a dynamical system and its dual, through nonlinear coupling elements, is shown to generate a pair of fundamental stationary principles. These provide a unified basis for both the classical Lagrangian and Hamiltonian treatments of dynamical systems aud modern work on nonlinear network theory and linear optimal-control theory. View full abstract»

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  • Dual-system methods in dynamical analysis. Part 2: Optimal regulators and optimal servomechanisms

    Publication Year: 1969 , Page(s): 1458 - 1462
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (446 KB)  

    Optimal-linear-regulator and servomechanism problems are treated in a unified and coherent way by the use of the variational properties of a pair of interconnected dual dynamical systems. View full abstract»

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  • Generalisation of D decomposition techniques

    Publication Year: 1969 , Page(s): 1463 - 1470
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1085 KB)  

    The technique of D decomposition has been generalised to provide what is believed to be the most powerful method presently available for the study, particularly the synthesis, of asymptotically stable, linearised, multiparameter autonomous systems. In particular, the method has been developed so that only one (any one) parameter need be restricted to appearing linearly in the characteristic equation. The other parameters may enter in any way whatsoever, so that it is virtually impossible to conceive of a practical system which does not fall within the scope of the method. Further, the method has been generalised so that not only the zero-damping case can be synthetised, but also the cases of arbitrarily specified degrees of absolute or relative stability. The method has been designed for use with a digital computer, and all essential algorithms required in its application are outlined. Special attention has been given to the general possibilities for the partitioning of an arbitrary characteristic equation, and as a result it has been found possible to develop procedures which permit the determination, in advance of any computation of the most efficient partitioning and parameter selection for any given problem. Comparisons are made with the Routh-Hurwitz method, and these show the Ddecomposition technique to be much the superior. Data has been published earlier showing the superiority of this method compared with root-locus methods. 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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