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Proceedings of the IEE  Part IV: Institution Mon...
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Volume 98
Issue 1
Proceedings of the IEE  Part IV: Institution Monographs
Volume 98, Issue 1, October 1951
Volume 98, Issue 1
October 1951
The effect of the Earth's magnetic field on shortwave communication by the ionosphere
 Author(s): G. Millington
 Source: Proceedings of the IEE  Part IV: Institution Monographs, Volume 98, Issue 1, p. 1 –14
 DOI: 10.1049/pi4.1951.0001
 Type: Article
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This paper is mainly a representation of the magnetoionic theory for oblique transmission through the ionosphere with special reference to numerical applications, but it is directed particularly to the problem of using ionospheric knowledge to plan shortwave longdistance communication. The quartic equation of the theory is solved graphically by the intersection of a straight line with a certain curve, and a chart is described for the construction of the latter for various values of the electronic density. By the method of stationary phase, simple expressions are obtained for the differential coefficients of the ray path, including the group time, lateral deviation and specific attenuation. Numerical integration along the ray path for a given density distribution is discussed with special reference to the relation of oblique to vertical transmission. Some preliminary results are given, but no detailed numerical survey is included, as this would more fittingly form the subject of a separate paper.
The dielectric breakdown of some simple organic liquids
 Author(s): B. Salvage
 Source: Proceedings of the IEE  Part IV: Institution Monographs, Volume 98, Issue 1, p. 15 –22
 DOI: 10.1049/pi4.1951.0002
 Type: Article
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The development of a method of measuring the electric strength of liquid dielectrics with direct current, alternating current and impulse voltages, is described.Experiments on normal hexane have shown that, when the electrode system is thoroughly cleaned and the liquid carefully filtered, the electric strength is independent of the form and duration of the applied voltage and the dielectric thickness. The electric strength cannot, however, be considered an intrinsic property of the liquid, since with direct current it is dependent on both the material and form of the electrodes.Investigations on a series of liquid normal paraffin hydrocarbons (pentane to nonane) have shown that the electric strength increases as the chain length of the molecule increases. The cyclic hydrocarbons, cyclohexane and benzene, have approximately the same electric strength as nhexane.The experimental results are discussed in relation to existing theories of dielectric breakdown in liquids and solids.
Application of the compensation theorem to certain radiation and propagation problems
 Author(s): G.D. Monteath
 Source: Proceedings of the IEE  Part IV: Institution Monographs, Volume 98, Issue 1, p. 23 –30
 DOI: 10.1049/pi4.1951.0003
 Type: Article
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The compensation theorem is often used to obtain the approximate effect of small changes in the elements of an electrical network. The paper describes an extension to a continuous system which includes, instead of a set of circuit elements, a boundarysurface exhibiting the property of surface impedance. The change in mutual impedance between two pairs of terminals situated outside this surface, due to a small change of surface impedance, is expressed as a surface integral. This result, which is deduced from an exact expression allied to Huygens's principle, simplifies the evaluation of the effect of imperfectly conducting ground upon the selfimpedance of an aerial placed above it, and enables account to be taken of the presence of an earth system. The effect of the earth system upon radiation from an aerial carrying a given current may also be obtained. Two propagation problems are considered, reflection at a land/sea boundary, and reflection at a cliff. An intermediate result is used in the case of cliff reflection, to which the concept of surface impedance is not applicable.
A general theory of sampling servo systems
 Author(s): D.F. Lawden
 Source: Proceedings of the IEE  Part IV: Institution Monographs, Volume 98, Issue 1, p. 31 –36
 DOI: 10.1049/pi4.1951.0004
 Type: Article
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A comprehensive mathematical theory of servo systems in which the difference between input and output quantities is examined discontinuously at the ends of equal intervals of time is developed, and general formulae are obtained from which the behaviour of any particular system may be deduced. These results are applied to obtain the fundamental equations of the two particular types of system which have been developed practically. Two examples of typical elementary systems are analysed. Recommendations for future work in this field are given.
Pulse distortion
 Author(s): S.H. Moss
 Source: Proceedings of the IEE  Part IV: Institution Monographs, Volume 98, Issue 1, p. 37 –42
 DOI: 10.1049/pi4.1951.0005
 Type: Article
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It is shown that for waveforms of simple shapes certain features may be defined: content, epoch, spread, skewness, squatness, etc., which are affected in a very simple way by passage through a linear system (which is regular^{*} at low frequencies). In fact, by proper definition, they are affected only additively by constants which are independent of the applied waveform, and characteristic only of the system. These invariants for the pulses and for the system, correspond to the cumulants used to describe statistical distributions.With due care, these results can be usefully generalized for a.c. wavepackets.
The relative advantages of coherent and incoherent detectors: a study of their output noise spectra under various conditions
 Author(s): R.A. Smith
 Source: Proceedings of the IEE  Part IV: Institution Monographs, Volume 98, Issue 1, p. 43 –54
 DOI: 10.1049/pi4.1951.0006
 Type: Article
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A comparison is made of the output spectra comprising signal and lowfrequency noise when a sinusoidal signal plus noise is applied to several types of detector. As typical of the incoherent type of detector the common squarelaw detector and the socalled linear detector have been studied. The coherent type is represented by the homodyne and commutator detectors. The comparison is made for input noise from several common types of filter.The signal/noise ratio at the output is calculated in terms of that at the input, and curves showing this relationship for the various types of detector are given, both for the case when no further bandwidth limitation is introduced other than the filtering out of the highfrequency components, and also for that when the detector is followed by a narrowband lowpass filter.It is shown that, provided certain precautions are taken, a very considerable gain in signal/noise ratio may be obtained by using the coherent detector when the input signal/noise ratio is somewhat less than unity. The actual amount of this gain for various circumstances may be read directly from the curves given in the text. This condition has not been of much practical importance until recently, but has now found many applications involving the detection of signals much below noise level by means of postdetector integration.The values of output signal/noise ratio for the various detectors are given for a range of values of the input signal/noise ratio in a series of figures, and the behaviour for large and small values of the latter is compared in Tables 1 and 2.
The calculation of the magnetic field of rectangular conductors in a closed slot, and its application to the reactance of transformer windings
 Author(s): E. Billig
 Source: Proceedings of the IEE  Part IV: Institution Monographs, Volume 98, Issue 1, p. 55 –64
 DOI: 10.1049/pi4.1951.0007
 Type: Article
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The magnetic vector potential of currentcarrying conductors in a rectangular slot is the same as that due to an infinite number of images of these conductors from all the four walls of the slot. A solution of this problem can thus be obtained in the form of a Fourier series, periodic in both the x and ydirections, the constants of the solution being determined by the boundary conditions, i.e. by the dimensions of the slot and of the conductors, and by the currents passing through them. Expressions for the magnetic vector potential due to any conductor arrangement can thus be developed, and these lend themselves to considerable simplification without undue loss of accuracy. Lines of magnetic flux density correspond to constant values of the vector potential, and this yields a ready method for plotting magneticflux maps. The results of this investigation can, with certain assumptions, be directly applied to transformer reactance problems and also to the equivalent problem of heat conduction of windings embedded in the slots of electrical machines. Formulae are developed for the reactance and forces in concentricwinding arrangements, showing the effects of slight asymmetries.
Design of electric wave filters with the aid of the electrolytic tank
 Author(s): A.R. Boothroyd
 Source: Proceedings of the IEE  Part IV: Institution Monographs, Volume 98, Issue 1, p. 65 –93
 DOI: 10.1049/pi4.1951.0008
 Type: Article
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The analogue representation of the properties (in terms of complex frequency λ) of imageparameter transfer functions of the Zobel type by currentflow in an electrolytic tank provides, in the first place, a convenient means of designing such filters, and it has the important consequence that the properties of these currentflow representations are found to lead to a process for the solution of the approximation problem in the insertionloss theory of filter design. The paper is in two parts, of which Part 1 is devoted to the representation of imageparameter transfer functions by the electrolytic tank. The electrolytic tank itself is first considered to be of the doublelayer form described in an earlier paper;^{2} for the accurate representation of functions of the filtering type, however, it is found more appropriate to work in a transformed version of the λplane in which the entire plane is represented in a finite rectangle—the electrolytic tank is then of particularly simple construction. In Part 2 of the paper, the use of the electrolytic tank as an aid to filter design on an insertionloss basis is described. A transformation is developed, by means of which the approximation problem can be solved for a lowpassfilter specification of insertion loss, the poles and zeros of the insertion modulus function of the filter being accurately determined by simple measurements on the electrolytic tank. The transformation itself follows from the properties of imageparameter functions considered in Part 1. Detailed design procedures are given, including provision for the effects of inherent dissipation in the reactance elements of the filter. It is also found possible to extend the method of design to a general, unsymmetrical bandpass filter, and to apply the basic principles to certain rootfinding operations involved in Darlington's method of network realization. Detailed examples and experimental results are given throughout the paper.
The resistance of roundwire singlelayer inductance coils
 Author(s): A.H.M. Arnold
 Source: Proceedings of the IEE  Part IV: Institution Monographs, Volume 98, Issue 1, p. 94 –100
 DOI: 10.1049/pi4.1951.0009
 Type: Article
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Butterworth's two formulae for the resistance of short coils with a finite number of turns and long coils with an infinite number of turns are merged into a single formula valid for coils of any length and having any number of turns. Numerical values of the functions appearing in the formula are given in tables. The formula is shown to give results in reasonable agreement with the experimental figures of Medhurst and Hickman.
Observations on the electrical breakdown of gases at 2800 Mc/s
 Author(s): W.A. Prowse and W. Jasinski
 Source: Proceedings of the IEE  Part IV: Institution Monographs, Volume 98, Issue 1, p. 101 –111
 DOI: 10.1049/pi4.1951.0010
 Type: Article
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Electrical discharges at 2800 Mc/s are produced in a nosedin cavity type of resonator by energizing it from a pulsed magnetron. Individual pulses of various durations in the range 0.25 microsec to 2.5 microsec are employed. Electrons are provided in mid gap by the short ultraviolet radiation from an auxiliary d.c. spark actuated from the circuit used to trigger the power pulse. Descriptions and illustrations are given of the form of the resulting discharge, which in typical cases begins in mid gap and advances towards the electrodes, crossing a 1cm gap in times of the order of 1 microsec. The discharges in different gases at atmospheric pressure show wide differences in appearance.Oscillograms of the envelope of the field in the resonator show a very rapid collapse when the discharge occurs; in certain gases, notably hydrogen, a striking consistency of behaviour is exhibited.Studies of the absorption coefficient of the active radiation from the auxiliary gap agree with the supposition that it lies in the short ultraviolet region, and it is found possible to calculate the variation of sparking probability with distance of the irradiating spark from the resonator. Confirmatory experiments with pulsed d.c. sparks support the argument.
Rotaing Htype Adcock directionfinders for metre and decimetre wavelengths
 Author(s): H.G. Hopkins and F. Horner
 Source: Proceedings of the IEE  Part IV: Institution Monographs, Volume 98, Issue 1, p. 112 –126
 DOI: 10.1049/pi4.1951.0011
 Type: Article
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An account is given of the development at the National Physical Laboratory of rotating Htype Adcock systems suitable for use at metre and decimetre wavelengths. Instruments of high precision for the range 26–600 Mc/s (0.5–12 m wavelength) are described, and details of their performance are given. The directionfinders at the tower end of this frequency range are of high sensitivity and have seen considerable practical service. At the higher frequencies the instruments are of an experimental nature, constructed with a view to examining the problems to be encountered in exploiting this part of the band.Development has proceeded largely on empirical lines, but from this work a fair appreciation has now been obtained of the fundamental factors affecting performance and of the practical means for taking them into account. Some progress has been made, for example, in understanding the cause of polarization errors, which are of importance in some—but not all—d.f. applications at these frequencies. The first half of the paper is therefore devoted to a discussion of these factors and to a description of certain common design features which have emerged.It is probable that, at frequencies above about 300 Mc/s, the application of groundbased simple Adcock systems will be limited by their inherently low sensitivity. This disadvantage may be partly overcome by the use of passive reflecting elements, and a system is described in which a sheet reflector is used in conjunction with an Htype Adcock aerial.
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