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Electrical Engineers, Proceedings of the Institution of

Issue 5 • Date May 1967

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Displaying Results 1 - 25 of 25
  • Propagation measurements at 3.6 and 11Gc/s over a line-of-sight radio path

    Publication Year: 1967 , Page(s): 545 - 549
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (646 KB)  

    The results of signal-level recordings at 3.6Gc/s and 11Gc/s made simultaneously for a 12-month period over a 55km line-of-sight radio path are given. Two types of fading were encountered: that due to interference between two or more rays and that due to absorption caused by atmospheric precipitation. An attempt is made to correlate the latter with precipitation rate. A method of measuring the changes in elevation angle of received rays at 11Gc/s is described, the results given, and possible effects on gain degradation of narrow-beam aerials are assessed. View full abstract»

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  • Effect of irregular fields on aperture reception characteristics

    Publication Year: 1967 , Page(s): 550 - 552
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (294 KB)  

    Formulas are given which describe the receiving properties of an aperture when the incident radiation contains a spatially irregular component, as may arise after propagation through an irregular medium. Results are derived for the degradation of power gain, the variance of the power output and the correlation between the outputs from spaced apertures. Illustrative numerical data are given for the special case of a Gaussian autocorrelation function for the random component of the original signal. View full abstract»

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  • Diffraction by a deeply modulated random-phase screen

    Publication Year: 1967 , Page(s): 553 - 556
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (425 KB)  

    A study is made of the intensity fluctuations of waves diffracted by a random screen which imposes large phase changes on an incident plane wave. Numerical results are given for the magnitude of the fluctuations as a function of the distance from the screen; the focusing effect previously found by Mercier is further investigated, and its distance from the screen is related to the magnitude of the phase modulation. The way in which the correlation of the signal intensity varies with the distance from the screen is also studied. The scale of the intensity fluctuations is always less than the scale of the phase fluctuations in the screen, but it may increase or decrease with increasing distance according to the depth of the phase modulation. View full abstract»

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  • Prediction of attenuation by rainfall in the 10.7¿11.7 GHz communication band

    Publication Year: 1967 , Page(s): 557 - 565
    Cited by:  Papers (8)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1550 KB)  

    An empirical relationship relating the mean quasi-instantaneous rainfall rate along a microwave path and the signal attenuation over the path at 11 GHz has been obtained and is compared with a theoretical formula derived by Ryde. A relationship between the annual distributions of several measured point rainfall rates for periods of 2, 10, 20 and 60min has also been obtained. This has been used, in conjunction with the empirical rainfall-rate/attenuation relationship and hourly point rainfall-rate distributions measured at points on several experimental 11 GHz microwave paths, to synthetise annual distribution curves of quasi-instantaneous attenuation due to rainfall according to a method proposed by Bussey. These curves are compared with characteristics measured on the paths. A method developed by the UK Post Office for predicting attenuation by rainfall at microwave frequencies is also described. Distributions of attenuation determined by this method for the experimental paths are also compared with the measured distributions. Several published methods of predicting hourly point-rate distributions from generally available coarse rainfall statistics have been examined which, if satisfactory, would have provided a powerful means in conjunction with the Bussey method for predicting the effect of rainfall on a microwave path. It is shown, however, that these methods give results which, when compared with measured performance, are far from satisfactory. Of the methods for predicting attenuation by rainfall studied, the Post Office method appears to justify most confidence and to be the easiest to use. View full abstract»

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  • Corona and precipitation interference in v.h.f. television reception

    Publication Year: 1967 , Page(s): 566 - 576
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1661 KB)  

    An investigation has been made into a type of interference occurring during thundery weather which may mar reception on v.h.f. In particular, it causes a degradation of the quality of pictures received in Britain for rebroadcasting purposes. Both laboratory and field experiments are described, from which the mechanisms giving rise to corona interference and precipitation interference are deduced. Protective measures are described which suppress the interference on horizontally or vertically polarised aerials by about 30dB. View full abstract»

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  • Isotropic directional transponder beacon. Replying in a direction determined by the incoming signal

    Publication Year: 1967 , Page(s): 577 - 580
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (550 KB)  

    A 3-dimensional multielement transponder array is proposed which will give directional replies towards the sources of interrogating signals. The potentialities and limitations of the principle are briefly analysed, and a number of variants and extensions of the basic scheme are considered. View full abstract»

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  • Direction-finding performance of a wide-aperture sampling linear array

    Publication Year: 1967 , Page(s): 581 - 588
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (883 KB)  

    The statistical performance of a 225m sampling linear array in h.f. direction finding is presented. Several methods of processing the sampled data are employed to investigate various aspects of system performance. The equivalence of time and space sampling in reducing the variance in the estimated direction of arrival is deduced from the results. View full abstract»

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  • Maximisation of directive gain for circular and elliptical arrays

    Publication Year: 1967 , Page(s): 589 - 594
    Cited by:  Papers (14)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (662 KB)  

    The paper begins with a general formulation of the gain-optimisation procedure for an array with an arbitrary geometrical configuration. The formulation is then specialised to apply to a planar array. In particular, extensive computed data for the maximum obtainable directive gain of circular and elliptical arrays are presented and compared with those with a uniform amplitude and cophasal excitation. For small element separations, a supergain situation results under optimum-gain conditions. A main-beam radiation efficiency is defined, which serves as an additional performance index. In a supergain situation, a proper design represents a suitable compromise between the directive gain and the main-beam radiation efficiency. View full abstract»

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  • Technique of fabricating inhomogeneous mediums and the behaviour of a dipole in such a medium

    Publication Year: 1967 , Page(s): 595 - 603
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1147 KB)  

    It is shown that an inhomogeneous medium to be used for antenna experiments can be fabricated using the diffusion profile of NaCl into agar agar. Various problems relating to the construction of a 316gal agar agar tank are described. The production of a desired profile of the electrical properties of the medium is discussed, together with the experimentally determined driving-point admittance and current distribution of a dipole antenna when immersed in the inhomogeneous conducting medium. The measured electrical properties of the agar agar when dissolved in tap water are ¿r = 78 and tan ¿ = 0.13 at 114 Mc/s and a conductivity of 0.8 mmho/cm at 1000c/s; the diffusion constant D of NaCl into 1.3% agar agar is 0.8¿2.0 × 10¿5cm2/s at 25°C. The range of change in the loss tangent is large; one profile varied from tan ¿ = 0.13 to tan ¿ = 3.3, which corresponds to a factor of 25 in the distance of a wavelength. The periods of diffusion were 1¿3 weeks. The properties of a dipole antenna measured in an inhomogeneous conducting medium are compared with those in a homogeneous conducting medium. View full abstract»

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  • Waveguide structures for double-beam leaky-wave antennas

    Publication Year: 1967 , Page(s): 604 - 610
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (860 KB)  

    The behaviour of two types of leaky-wave antenna is described, where more than one mode of propagation is supported in the leaky waveguide. The radiation pattern of such antennas contains one main lobe for each mode of propagation, and the design of a double-beam antenna is studied in some detail. First, consideration is given to a slotted double-ridge waveguide. It is shown both theoretically and experimentally that the structure can be designed so that pairs of higher-order modes cause radiation of nearly independent beams at angles which are closely spaced. When H02 and H03 modes are used for this purpose, the structure has the disadvantage of also supporting, at the operating frequency, the H01 mode and a slot mode. These undesired modes may be eliminated if an inductive, rather than capacitive, form of coupling is used between the constituent waveguides and if the radiating waveguide wall also has an inductive reactance. The reactance is realised by means of circular-cross-section coupling holes spaced periodically along the waveguide. Theoretical and experimental results for this structure are shown to compare favourably, and problems associated with the extension of the principle to antennas radiating more than two independent beams are briefly mentioned. View full abstract»

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  • Noise in transistor mixers at low frequencies

    Publication Year: 1967 , Page(s): 611 - 618
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1000 KB)  

    The paper deals with the noise performance of transistor mixers at frequencies where reactive effects may be neglected (generally less than 0.1fT). The analysis involves the consideration of noise processes in a time-varying circuit, and the problem is treated by returning to the basic physical equations describing the transistor. The problem of noise in the transistor-base current is discussed in detail. The analysis allows a simple prediction of transistor-mixer noise figure at low frequencies, and the effects of variation in local-oscillator drive, source resistance, transistor parameters and operating current are readily predicted. The emphasis is on an engineering approach to the problem, and the results are presented in a form intended to facilitate the design of low-noise mixers. View full abstract»

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  • New international switching and transmission plan recommended by the CCITT for public telephony

    Publication Year: 1967 , Page(s): 619 - 627
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1407 KB)  

    In order to lay the foundation of a worldwide telephone network that will eventually provide fully automatic international subscriber dialling between any two subscribers anywhere in the world, the CCITT, at its 3rd Plenary Assembly in 1964, recommended the principles of new routing, numbering, switching and transmission plans for international public telephony. The paper briefly describes the routing plan and gives a more detailed explanation of the switching and transmission aspects of the new recommendations. View full abstract»

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  • Sensitivity optimisation in active RC-network synthesis

    Publication Year: 1967
    Save to Project icon | PDF file iconPDF (105 KB)  
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  • Representation of faults in the dynamic simulation of h.v. d.c. systems, by digital computer

    Publication Year: 1967 , Page(s): 629 - 638
    Cited by:  Papers (8)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1230 KB)  

    The paper introduces and develops digital-computer techniques for the representation of faults in the dynamic simulation of h.v. d.c. systems. The authors have employed the central-process method of representation, which is based on the fact that h.v. d.c. convertor operation consists of similar consecutive processes. This method enables convertor bridges, their control systems, the transmission line and the a.c. systems to be represented as a mathematical model by a set of differential, algebraic and Boolean equations. Repetitive use of the central-process technique enables continuous h.v. d.c. system operation to be represented under normal and abnormal conditions. The resulting digital-computer program, in which the system parameters are represented numerically, provides a versatile, accurate and inexpensive means of studying the response of an h.v. d.c. system to a specified condition. It is, for some purposes, an alternative to a physical model. The program described in the paper represents dynamically a complete 2-bridge h.v. d.c. system. Some of the transient waveforms of system voltages and currents resulting from convertor faults such as backfire, failure to fire, fire through, and commutation failure are given in the paper. View full abstract»

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  • Standardisation and approval of electrical equipment for use in hazardous atmospheres

    Publication Year: 1967 , Page(s): 639 - 644
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1108 KB)  

    As a result of the increasing use of electrical equipment in situations where there is a potential explosion hazard owing to flammable gases and vapours, there is considerable international activity in the preparation of new and revised standards for the design and use of such equipment. This review compares the present position in Britain with the position abroad, with regard both to methods of protection and application and to the equally important procedures of certification and approval of equipment. As it has recently been proposed that a new organisation should be set up to rationalise the procedures in Britain, the ways in which such an organisation can help to maintain the UK position in this field are examined. The review has been confined to the situation in the nonmining industries, although some of the matters discussed apply equally to the mining industry. View full abstract»

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  • Developments in the performance and theory of segmental-rotor reluctance motors

    Publication Year: 1967 , Page(s): 645 - 653
    Cited by:  Papers (25)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1216 KB)  

    The paper describes some of the improvements that have been achieved, both experimentally and theoretically, in reluctance motors with purely segmental rotors. These improvements result from incorporating a shallow axial channel in the centre of the air-gap face of each segment, filling of this channel with conducting material, shaping of the ends of the segments and optimisation of the significant design parameters. It is shown that, when synchronising duties are light, the maximum pullout torque of a reluctance machine can exceed the breakdown torque of the equivalent induction machine (so that its pullout power considerably exceeds the breakdown power of the induction machine) and that maximum power factors better than 0.8 are possible. Careful attention is given to the asynchronous-performance characteristics, with particular reference to the synchronisation of load inertias of two to three times the rotor inertia (the most usual values). It is found that pullin powers greater than 90% of the induction-motor full-load powers and power factors up to 0.74 are possible. Of considerable importance, particularly in connection with thyristor-invertor supplies, is the fact that starting currents are low?about four times full-load current. Efficiencies up to 90% may be expected, even in relatively small machines. The development on the theoretical side includes (a) the generalisation of earlier results to include the effects of the channel in, and the end shaping of, the magnetic segments, and (b) the elimination, through the consideration of harmonics of permeance and rotor potential, of the need for an empirical factor in calculation of the quadrature-axis reactance. Stator-winding harmonics are considered, but it is shown that their effects are small. It is also found that losses due to the generation of high-frequency currents are small. Calculated and measured values for both reactances and synchronous-performance characteristics are shown to agree very closely ove- r the whole range of parameters. The performances claimed here have been fully confirmed by tests on a commercial machine of approximately 10hp rating. View full abstract»

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  • Variable-characteristic d.c. machines

    Publication Year: 1967 , Page(s): 654 - 655
    Save to Project icon | PDF file iconPDF (302 KB)  
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  • Polyphase induction motor with single-phase rotor

    Publication Year: 1967 , Page(s): 655 - 656
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (204 KB)  

    First Page of the Article
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  • Characteristics of an arc discharge in sulphur hexafluoride

    Publication Year: 1967 , Page(s): 657 - 660
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (463 KB)  

    Voltage gradients and electrode-fall voltages have been measured for an SF6 arc burning in a 6.35mm-diameter tube. The voltage gradients are lower than those in a nitrogen arc, the reason being that the thermal conductivity of the SF6-arc plasma is lower, than that of a nitrogen plasma. Using previously calculated electrical and thermal conductivities the theoretical voltage gradients agree very closely with those measured. Also, the radial temperature distributions for various SF6 arcs have been calculated, the agreement with the measured distributions obtained by Maecker and Motschmann being very good. For low currents, the calculated temperature distributions show that the SF6 arc is very narrow and filamentary compared to an arc in nitrogen or air; this is in agreement with visual and photographic observations. The main reason for this is the dissociation of the SF6 molecule at a temperature of 21000°K, resulting in a large peak in the thermal conductivity. Thus the time constant of the SF6 arc is much lower than that of the nitrogen arc. This, coupled with the dastic reduction of the electron concentration below 5000°K by the formation of negative fluorine ions, results in the excellent arc-quenching properties of the gas. View full abstract»

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  • R.F. permeability measurements of ferrite aerial rods

    Publication Year: 1967 , Page(s): 661 - 664
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (568 KB)  

    Normally, the magnetic properties of ferrites, such as permeability and losses, are determined by measurements on ring samples. Extruded products, however, are mostly anisotropic, so that data obtained from rings cut out of the rods are not representative of the properties of the extrusions. The paper deals with the measurement of the initial permeability of ferrite rods at high frequencies (about 300kc/s). Rods with rectangular as well as circular cross-sections have been tested. In all cases, the initial permeability is determined by measuring the amplitude permeability in terms of peak magnetising force and peak magnetic flux density at low flux densities. The methods investigated are (a) measurement using a tangential-field coil, (b) an a.c. version of the Iliovici permeameter and (c) measurements by means of a magnetic potentiometer. View full abstract»

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  • Analogue of cylindrically symmetric fields using teledeltos paper

    Publication Year: 1967 , Page(s): 664 - 665
    Save to Project icon | PDF file iconPDF (268 KB)  
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  • Self-adjustable orthogonal digital filters for system identification and optimisation

    Publication Year: 1967 , Page(s): 666 - 670
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (546 KB)  

    The paper describes the application of orthogonal systems of functions to the problem of designing digital filters with independent adjustable parameters for the open-loop control of processes. A computational algorithm is given for designing the digital filter and is applied to the problems of process identification and the determination of discrete compensators for optimum closed-loop control systems. Digital-simulation methods are employed to obtain experimental results to illustrate the techniques. View full abstract»

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  • Overall station control at Hunterston A

    Publication Year: 1967 , Page(s): 671 - 678
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (893 KB)  

    Design or analysis of nuclear-power-plant overall-control systems involves transient representation the behaviour of the reactors, boilers, turbines and ancillary plant. The representation of 2-phase transient heat transfer in evaporators and the transient behaviour of steam drums is particularly important. Typical system representations may contain 150 ordinary differential equations, many of them nonlinear. These are solved on analogue or digital computers; the system general controllability is first established, suitable values for the control parameters are determined, and the system behaviour in normal operating and fault conditions is then studied in detail. Commissioning-test transients are simulated for guidance during system commissioning; the test results establish the suitability of the control system and the validity the analytical approach. In the paper the development of the representation of the overall plant-control system of the Hunterston nuclear generating station is outlined. Examples are given of transients predicted analytically and obtained in practice. The test results show that the system works satisfactorily, and suggest that an analytical approach of the complexity outlined enables the behaviour of the plant and control system to be predicted adequately from the practical point of view. View full abstract»

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  • Design and application of a stochastic analogue computer

    Publication Year: 1967 , Page(s): 679 - 688
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1164 KB)  

    It is shown that a fast analogue representation of Laplace's equation and the diffusion equation may be obtained using a Monte Carlo method, and a number of problems are examined involving various boundary configurations. An analysis of errors of solution is included, and the paper also presents a graphical technique for obtaining the switching points in a time-optimal problem for a distributed-parameter plant. View full abstract»

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  • Construction of the generalised functional matrix

    Publication Year: 1967
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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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