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Electrical Engineers, Proceedings of the Institution of

Issue 5 • Date May 1966

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Displaying Results 1 - 25 of 38
  • Class-AB amplifiers employing a complementary pair of transistors

    Page(s): 721 - 724
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (306 KB)  

    This paper describes a method of applying current negative feedback to transformerless audio class-AB transistor stages, and analyses the distortion problem in some detail. The output impedance of the circuit is very high, but the circuit may also be conveniently adapted to provide a matched output resistance, for example, for a 600¿ line. View full abstract»

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  • Theoretical assessment of the use of pulse compression in a panoramic receiver

    Page(s): 725 - 739
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1390 KB)  

    The paper presents a theoretical investigation of the application of the pulse-compression technique to a panoramic superheterodyne receiver. The sensitivity and resolution of such a system have been calculated and compared with those of a receiver without compression. Receivers having square-law or linear detectors, with both rectangular and Gaussian i.f. responses, have been considered. For the receiver without compression, the calculated sensitivity is that of the tangential setting; for the receiver with compression a similar calculation is made, based on the peak power of the compressed pulse. For a given receiver bandwidth, B1, and a sweep rate, R, the sensitivity improvement has a theoretical upper limit of approximately B21/R. Practical limitations to the magnitude of the increase are, however, set by the ability to design and construct suitable, dispersive delay networks operating over a wide frequency band, by unintentional variations in the sweep rate and by the possible difficulty of maintaining a good noise factor in a very wideband receiver where the i.f. extends to a very high frequency. In practice, improvements in sensitivity of up to 20dB should be possible. Information is also given for the design of a panoramic receiver without pulse compression. View full abstract»

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  • Effect of distortion on the Bessel-zero method of frequency-deviation measurement

    Page(s): 740 - 746
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (861 KB)  

    The Bessel-zero technique for f.m. deviation measurement is often used as the standard for the calibration of carrier-deviation and f.m.-signal-generator instruments. Error in the calculation of the deviation arises owing to harmonic distortion in the modulating signal, which results in a change in the value of the modulation index at which the carrier amplitude is zero. Similar errors occur when spurious amplitude modulation arises because of variation in the loading and dynamic impedance of the tuned circuit during frequency modulation. The paper examines quantitatively the effects of both types of distortion on the modulation index. It is considered that, in practice, zeros greater than, say, the 12th, are rarely used, and percentage distortions greater than 10% are very unlikely. Using these assumptions, `worst-case¿ errors are calculated. The largest error appears to arise from spurious amplitude modulation at the second harmonic of the modulating frequency, and is less than 4% for up to 10% distortion. The actual measurement of the errors is very difficult because they are extremely small. The theoretical analysis confirms this, and indicates the tolerable distortion for a given accuracy of the method. View full abstract»

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  • Groundwave propagation along three-section mixed paths

    Page(s): 747 - 751
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (643 KB)  

    Recent theoretical work on the propagation of groundwaves along 2-section mixed paths is extended to 3-section paths. A corroborating experiment was conducted at a microwave frequency of 4.29 Gc/s (¿ = 7 cm), using water to simulate imperfectly conducting mediums and aluminium plates to simulate perfectly conducting mediums. The experimental results show that the theoretical solutions are accurate to within a few per cent., provided that both aerials are at least a fraction of a wavelength from the separation boundaries. View full abstract»

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  • Propagation in isotropic plasma waveguides

    Page(s): 755 - 766
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1457 KB)  

    The paper considers the propagation behaviour of a circular waveguide enclosing either an axial or an annular column of isotropic plasma. The effect of the glass walls of the container required to enclose an actual gaseous plasma is exactly taken into account. The phase-change and attenuation coefficients of both structures are computed for a range of parameters relevant in microwave applications. It is evident that the circularly symmetric mode of the axial column has characteristics suited to devices employing forward waves, whereas the circularly symmetric mode of the annular structure is suited to devices employing the backward wave. A brief review of possible passive- and active-device applications of the structures is presented and some of the limitations on the realisation of these devices noted. An equivalent transverse-network representation for a radially stratified isotropic structure is presented in the Appendix, thereby making possible the computations described in the paper. View full abstract»

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  • Performance-defining parameters of radio-navigational aids

    Page(s): 767 - 774
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1002 KB)  

    In its broadest aspect, the object of the paper is to draw attention to the need for a formal theory of radiolocation. An approximate analogy is drawn between the time, about 20 years ago, when the ?knowhow? of the experienced communication engineer was being translated into a formal theory of communication, and the present time, when, despite the existence of a corresponding expertise in the field of radiolocation, no serious attempt has been made to define a formal theory. In radiolocation, the concept of trading ?aperture? or ?baseline? for accuracy, very closely allied to the concept of trading frequency bandwidth for suppression of noise in communication systems, is very well known, and has probably been fully exploited, but theoretical limits have not yet been defined. The further concept that the frequency bandwidth of a radiolocation signal can also be traded for error suppression, though not new, has probably not been fully explored, and certainly not fully exploited. It is therefore a major object of the present paper to draw attention to this important aspect. A complete assessment of the value of an increased frequency bandwidth is not attempted, and no attempt is made to define an ideal system. However, by analysing a comparatively simple and practicable system which employs wide-deviation frequency modulation, and lends itself to a simple mathematical treatment, it is shown that a great improvement is possible. A simple aircraft approach-path guidance system comprising two laterally spaced, synchronously frequency-modulated transmissions is shown to have a greatly improved error-suppression characteristic, compared with conventional systems. The concept of ?effective bandwidth?, as already used in communication theory, is introduced, showing that, though the frequency bandwidth used by a single location device may be very large, this may not be prohibitive, as a number of devices may share the same frequency band without mutual interference. This leads- to a suggestion for a new aircraft guidance system providing azimuth indication, as in VOR, approach-path guidance, distance-to-fly indication, glide path and distance along runway, all on a single radio-frequency channel. View full abstract»

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  • RC active synthesis procedure for polynomial filters

    Page(s): 777 - 782
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (538 KB)  

    The design procedure presented in the paper allows active RC realisation of transfer functions of the general type H/a0+a1+a2x2+¿+anxn where x = p, the complex transform frequency variable, or its reciprocal 1/p. The fundamental idea is to consider the required network as a matrix upon which the desired transfer function imposes certain constraints. The passive-RCnetwork-component values are defined by the matrix elements, which, in turn are derived from the roots of the approximation polynomial. The active devices used in this procedure are nonideal low-gain amplifiers, the precise specifications of which are obtained from the matrix in exactly the same way as the passive component values. Although an understanding of node and mesh matrix analysis is required for the theoretical part of the paper, a working knowledge of the actual synthesis procedures can be obtained from the fifth-order design example which runs parallel with the theory throughout. View full abstract»

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  • Synthesis with negative resistors

    Page(s): 783 - 787
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (527 KB)  

    In the realisation of networks for higher frequencies, the usual tendency of avoiding inductors is not always justifiable. In the paper, several realisation techniques for driving-point functions, using all three standard components (RLC) and a single negative resistor, are proposed. A realisation based on Darlington's procedure is applied to the synthesis of a broad class of functions, called negative real functions, It is shown how any real rational function may be converted into a negative real one by the techniques of predistortion and resistance padding. Some constraints are given for a function to be realisable by applying a tunnel diode instead of the negative resistor. A modification of an RC-n.i.c. synthesis procedure is presented, resulting in a transformerless realisation of any rational function by means of an RLC network with a single negative resistor. Synthesis of a function having either its zeros or its poles in the left half of the complex-frequency plane is shown to be possible through partial-fraction expansion, combined with the use of a negative resistor. The resulting network is transformerless, and presents a very simple topology. Constraints on functions realisable by RLC components and tunnel diodes are discussed. View full abstract»

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  • Dynamic simulation of h.v.d.c. transmission systems on digital computers

    Page(s): 793 - 802
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1010 KB)  

    The paper introduces and develops a new digital-computer technique for the dynamic study of an h.v.d.c. system. The authors have called this technique the `central-process¿ method, and it is based on the fact that the operation of an h.v.d.c. convertor consists of similar consecutive processes, each process having features which are common to all processes. In this method, each bridge convertor of an h.v.d.c. system is represented by a central process, and repetitive use of the latter simulates continuous convertor operation. These central processes are mathematically represented by a set of differential and Boolean equations. Any h.v.d.c. system may be represented by mathematical connection of central processes simulating the connection of bridges in a true system. This technique may be employed to obtain the waveforms of transient or steady-state voltages and currents anywhere in the d.c. system. To illustrate this method, an h.v.d.c. link is considered; the link which connects two independent a.c. systems comprises two convertors with their control systems, and a d.c. transmission line. As an example, the transient behaviour of the system is examined, following changes in the current settings of the control system. View full abstract»

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  • Dynamic-programming approach to the selection and timing of generation-plant additions

    Page(s): 803 - 811
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1215 KB)  

    Many basically different types of generating units, such as nuclear, hydroelectric, steam- and gas-turbine units, could be added to a generating system to meet constantly growing installed-capacity requirements. Since each of these types may also vary considerably in capital cost, size, efficiency, fuel and site location, there are a very large number of possible choices each time a new generating unit is needed. Moreover, once a unit is purchased, its known capital fixed charges continue for the life of the plant, while its fuel and operating costs will initially depend on the composition and characteristics of the system prior to the installation of the new unit, later depending also on the relative efficiencies of units added subsequently, since these will directly affect the future power and energy supplied by the new unit to the system. In order to evaluate the economic merits of a particular type and size of unit to be added to a particular system, it is therefore necessary to determine the total costs associated with this choice over the projected life of the unit, in conjunction with each of the many thousands of combinations of future units that might be added during this lifetime period to be studied. At any stage in the process of making these decisions, the correct choice cannot be made without considering all possible decisions that might have been made during earlier stages and that might be made in future stages. The paper describes a dynamic-programming application to this particular problem, which, by eliminating many alternatives during each stage or year of a long-range study period, reduces the number of possible choices to proportions that can be handled and evaluated by a medium-sized digital computer, when using relatively simple reserve-capacity-requirement and production-cost logic, but which can become an exceptionally accurate tool in system-planning studies when programmed for use on a large computer. View full abstract»

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  • Eddy-current shielding of transformer tanks

    Page(s): 815 - 818
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (375 KB)  

    Transformer-tank losses can be reduced by lining the tank with a nonferrous material. A method is presented whereby the eddy-current density and tank flux can be obtained for a transformer with any number of windings and any distribution of turns. As a special case, solutions are obtained for a 2-winding transformer with uniformly distributed turns. View full abstract»

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  • Digital computation of induction-motor transient torque patterns

    Page(s): 819 - 822
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (465 KB)  

    A general approach to the digital computation of induction-motor transients is outlined and applied to the evaluation of torque/time patterns for a 3-phase induction motor. Results are given for simultaneous and nonsimultaneous connection to the supply terminals at speeds of zero and 90% of synchronous value. These computed patterns are compared with corresponding experimental recordings, and it is suggested that any differences in the torque-peak magnitudes are mainly due to nonrigidity of the rotor. View full abstract»

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  • General theory of eddy-current couplings and brakes

    Page(s): 825 - 837
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1433 KB)  

    The general steady-state theory of eddy-current coupling is extended and new material included. The differences in operation between salient-pole and inductor-type eddy-current couplings are shown and the limitations of inductor couplings emphasised. The peak torque of the inductor coupling is shown to be roughly half that of the Lundell machine and to occur at a much higher slip, giving considerable difference in low-slip performance. Tests taken on an experimental model, which are given in some detail, are shown to verify the theory. The appendix discusses the optimisation of eddy-current couplings of all types, based on the theory given in the paper. This gives the best airgap configuration for maximum low-slip torque, taking into account saturation and the presence of a parasitic airgap. The best pole shapes for torque production are also derived. View full abstract»

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  • Electricity for grain drying

    Page(s): 838 - 846
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1546 KB)  

    Grain is the most important farm crop in England and Wales. Modern harvesting methods have made drying necessary in most seasons, if the grain is to be kept on the farm for long periods. To this end, 27000 driers are now in use. The grain driers can be electrically powered and heated; the paper outlines the principles of drying, describes the types of drier which have been developed and indicates how electricity can best be applied. Although much of the information given is concerned with the design and operation of equipment, the subject has been approached from the point of view of the electricity-supply engineer. Comparisons of load factor, maximum demand, consumption and revenue returns are given for various types of drier operating under different conditions. Developments in other methods of storing grain may supersede drying in the future, but present indications are that electricity will continue to be needed for ancillary purposes. 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.

Full Aims & Scope