Electrical Engineers  Part III: Radio and Communication Engineering, Journal of the Institution of
The Journal of the Institution of Electrical Engineers  Part III: Radio and Communication Engineering was published by the IET between 1945 and 1948.
Latest Published Articles

Multipath interference in television transmission
Jan29 2010 
The authors' reply to the discussions on Â¿The development of polythene as a highfrequency dielectricÂ¿
Jan29 2010 
The authors' reply to the discussion on Â¿The calculation of field strengths over a spherical earthÂ¿
Jan29 2010 
The measured performance of horizontal dipole transmitting arrays
Jan29 2010 
A Method of Calibrating StandardSignal Generators and RadioFrequency Attenuators
Jan29 2010
Popular Articles

The propagation of electric waves in a rectangular wave guide
Jan29 2010 
Theory of communication. Part 1: The analysis of information
Jan29 2010 
The Electrical Constants of a Material Loaded with Spherical Particles
Jan29 2010 
The Fundamental Principles of Frequency Modulation
Jan29 2010 
Theory of communication. Part 2: The analysis of hearing
Jan29 2010
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1. The propagation of electric waves in a rectangular wave guide
This paper calculates the field, inside a rectangular wave guide, produced by a given set of currents at the origin. In particular, if the guide is excited by a single current filament on its midline then the field is found per unit current in this filament and also the radiation resistance of the filament. The solution is generalized to apply to a guide with a closed end. In Appendix 8.2 is calculated the field per unit current when the wave guide is very narrow, being then commonly called an attenuator. The solution for the guide is more complete than those which are common knowledge, in so far as the field is related to the current producing it, and this extension may be novel. In order to assess the sensitiveness of the classic solution to the exact form of the guide, the solution is found for a guide which has a vanishingly small taper. Then it is found that perfect cutoff cannot occur even when the width of the guide at the exciting filament is less than ??: the explanation is that in such a guide of infinite length there is often a point at which the width exceeds ??. It seems probable from this that complete cutoff will not occur if the generator is situated in a length of guide whose width is less than ??, provided this length is joined to a guide whose width exceeds ??. However, it appears that the expression for the radiation resistance of a current sheet, with sinusoidal loading, is general and applies to a guide having any taper, and in particular when the taper is zero and the sides have become parallel. It is concluded from this that the expressions for radiation resistance are very tolerant to small imperfections in the shape of the guide, and, in general, that the wellknown and classic solution is very reliable for practical application, provided only that the cutoff property is not interpreted with complete rigour. For the sake of completeness the formal solution is recorded for a current filament at any point in a tapered guide which has a co nvex back of any radius; and also the solution for a current enclosed in a box having two sides which are arcs of concentric circles of any radius and two sides which are any radii of these circles. These two solutions are thought to be novel. View full abstract»

2. Theory of communication. Part 1: The analysis of information
Page(s): 429  441Hitherto communication theory was based on two alternative methods of signal analysis. One is the description of the signal as a function of time; the other is Fourier analysis. Both are idealizations, as the first method operates with sharply defined instants of time, the second with infinite wavetrains of rigorously defined frequencies. But our everyday experiencesÂ¿especially our auditory sensationsÂ¿insist on a description in terms of both time and frequency. In the present paper this point of view is developed in quantitative language. Signals are represented in two dimensions, with time and frequency as coordinates. Such twodimensional representations can be called Â¿information diagrams,Â¿ as areas in them are proportional to the number of independent data which they can convey. This is a consequence of the fact that the frequency of a signal which is not of infinite duration can be defined only with a certain inaccuracy, which is inversely proportional to the duration, and vice versa. This Â¿uncertainty relationÂ¿ suggests a new method of description, intermediate between the two extremes of time analysis and spectral analysis. There are certain Â¿elementary signalsÂ¿ which occupy the smallest possible area in the information diagram. They are harmonic oscillations modulated by a Â¿probability pulse.Â¿ Each elementary signal can be considered as conveying exactly one datum, or one Â¿quantum of information.Â¿ Any signal can be expanded in terms of these by a process which includes time analysis and Fourier analysis as extreme cases. These new methods of analysis, which involve some of the mathematical apparatus of quantum theory, are illustrated by application to some problems of transmission theory, such as direct generation of single sidebands, signals transmitted in minimum time through limited frequency channels, frequency modulation and timedivision multiplex telephony. View full abstract»

3. The Electrical Constants of a Material Loaded with Spherical Particles
Page(s): 65  68The paper investigates the values of permittivity and permeability of a mixture consisting of a homogeneous material in which particles are embedded. Formulae are found which are valid at high frequencies, so long as the size of the particle is small compared with the wavelength and the packing is not too great. Special cases treated are irondust cores and expanded dielectrics in which the Â¿particlesÂ¿ are air bubbles. For ferromagnetic materials, weak fields only are assumed, so that the results refer to initial permeability. On account of the heterogeneity of the mixture, the permeability may become Â¿lossyÂ¿ (i.e. Â¿ may be complex). Even when the substances are all nonferromagnetic, the permeability of the mixture may depart from unity, or be complex. View full abstract»

4. The Fundamental Principles of Frequency Modulation
Page(s): 153  158First Page of the ArticleView full abstract» 
5. Theory of communication. Part 2: The analysis of hearing
Page(s): 442  445The methods developed in Part 1 are applied to the analysis of hearing sensations, in particular to experiments by Shower and Biddulph, and by BÃ¿rck, Kotowski and Lichte on the discrimination of frequency and time by the human ear. It is shown that experiments of widely different character lead to welldefined threshold Â¿areas of discriminationÂ¿ in the information diagram. At the best, in the interval 60Â¿1 000 c/s the human ear can discriminate very nearly every second datum of information; i.e. the ear is almost as perfect as any instrument can be which is not responsive to phase. Over the whole auditory range the efficiency is much less than 50%, as the discrimination falls off sharply at higher frequencies. The threshold area of discrimination appears to be independent of the duration of the signals between about 20 and 250 millisec. This remarkably wide interval cannot be explained by any mechanism in the inner ear, but may be explained by a new hypothetical effect in nerve conduction, i.e. the mutual influence of adjacent nerve fibres. View full abstract»

6. Some aspects of the design of balanced rectifier modulators for precision applications
Page(s): 161  172The design of balanced rectifier modulators of ring and Cowan types is discussed, and it is shown how the performance of the modulator depends on rectifier characteristics, the circuit impedance in which the modulator operates, the resistance of the carrier generator and the carrier voltage. The main performance features discussed are efficiency, stability, production of unwanted modulation products, impedance, and carrier leak. It is shown that there are advantages in designing a modulator for maximum efficiency by choosing a circuit impedance of optimum value and a carrier supply of high resistance. Variations in efficiency due to variations in carrier voltage, circuit impedance and temperature are then a minimum although it may be necessary to have each rectifier shunted with a constant resistance to achieve this. The production of modulation products of higher order is greatest in a modulator of maximum efficiency in which the circuit providing the carrier is of high resistance, and is reduced considerably if inefficient working and a lowresistance circuit are used. Further reduction, if desired, can be obtained by the use of a large bias on the rectifiers, and it has been found possible to reduce the 3fc?f sidebands to over 26 db below the fc + f sidebands (where fc = carrier frequency and f = signal frequency). This method is of value only in ring modulators, as with the Cowan circuit it introduces products of the type 2fc + f. It is shown that the ordinary potentiometer adjustment for carrier leak compensates only the unbalances between the low forward resistances of the rectifiers, and there remains an outofbalance current at small values of the instantaneous carrier voltage. This effect can be reduced by using a highresistance carrier supply and by appropriate selection of the rectifiers; a further improvement, in the case of ring modulators, can be obtained by the use of large biases on the rectifiers. Carrier leaks as low as ? 60 db relative to 1 volt in 600 ohms, or 40 db below sidebandlevel, when highlevel signals are applied, can readily be obtained and maintained in modulators with at least 1 volt carrier peak voltage across the rectifiers. It is assumed throughout that the rectifiers are purely resistive, as with the diodes and crystal valves now available, the effect of the capacitance is negligible up to frequencies of the order of 1 Mc/s. A method of design of a ring modulator is described in which the input impedance remains relatively constant over the cycle of carrier voltage; this may have important applications in precision circuits. View full abstract»

7. The Calculation of Amplifier Valve Characteristics
Page(s): 138  152The anodecurrent/gridvoltage characteristics of valves are determined with the help of diagrams and design charts based on Langmuir's data on the current flow in plane diodes with consideration of initial electron velocities, and on Oertel's and Herne's equations for the amplification factor. The theory is extended to multigrid valves and to valves possessing a more complicated shape. Special attention is given to the Â¿variablemu effect,Â¿ which represents one of the limiting factors in practical valve construction. A simple expression describing this effcct is derived, and a chart of the Â¿variablemu constant,Â¿ Â¿, is presented, in which space charge is taken into account. Measurements on specially made experimental valves and on several types of modern massproduced valves confirm the treatment of the variablemu effect and show that the methods outlined in the paper, forming a complete design system, allow the prediction of the static valve characteristic with good accuracy even in closely spaced modern valves. Finally, the influences of a change in controlgrid wire diameter, of a statistical variation of controlgrid pitch, and of cathode misalignment, are discussed. View full abstract»

8. Theory of communication. Part 3: Frequency compression and expansion
Page(s): 445  457It is suggested that it may be possible to transmit speech and music in much narrower wavebands than was hitherto thought necessary, not by clipping the ends of the waveband, but by condensing the information. Two possibilities of more economical transmission are discussed. Both have in common that the original waveband is compressed in transmission and reexpanded to the original width in reception. In the first or Â¿kinematicalÂ¿ method a temporary or permanent record is scanned by moving slits or their equivalents, which replace one another in continuous succession before a Â¿window.Â¿ Mathematical analysis is simplest if the transmission of the window is graded according to a probability function. A simple harmonic oscillation is reproduced as a group of spectral lines with frequencies which have an approximately constant ratio to the original frequency. The average departure from the law of proportional conversion is in inverse ratio to the time interval in which the record passes before the window. Experiments carried out with simple apparatus indicate that speech can be compressed into a frequency band of 800 or even 500 c/s without losing much of its intelligibility. There are various possibilities for utilizing frequency compression in telephony by means of the Â¿kinematicalÂ¿ method. In a second method the compression and expansion are carried out electrically, without mechanical motion. This method consists essentially in using nonsinusoidal carriers, such as repeated probability pulses, and local oscillators producing waves of the same type. It is shown that one variety of the electrical method is mathematically equivalent to the kinematical method of frequency conversion. View full abstract»

9. The Theoretical Precision with which an Arbitrary RadiationPattern may be Obtained from a Source of Finite Size
Page(s): 363  370It appears that it is possible to approximate as closely as desired to a specified radiationpattern by a suitable distribution of field over an aperture of given size, though the necessary currents in the conducting elements of the source would in general be prohibitively large in comparison with the power radiated. The difficulty of obtaining a high degree of approximation, and in particular a power gain very much greater than that of a uniformly illuminated aperture, is thus a practical rather than a theoretical one. The same is true for the linear array of given length as for the continuous aperture if no limit is set to the number of elements. Even when this number is limited by the adoption of halfwavelength spacing, the broadside power gain is not a maximum when the amplitudes and phases of the elements are equal, unless the elements are ideal isotropic pointsources. View full abstract»

10. The Theory and Experimental Behaviour of RightAngled Junctions in RectangularSection Wave Guides
Page(s): 177  187The paper opens with a general theoretical analysis of a waveguide junction of n members in terms of an equivalent transmission line system. This is then applied to the particular case of a rightangled junction in a guide of rectangular section excited in the H01 mode. The behaviour is expressed in terms of six parameters, the values of which have been calculated over a range of wavelengths around 10 cm and determined experimentally at four points within this range. A description of the experimental technique employed is given, and an assessment made of the order of accuracy attained in the measurements. View full abstract»

11. Matrix Methods in the Solution of Ladder Networks
Page(s): 40  50The matrix algebra has a natural application to electric circuit theory, especially to the method of solution by means of substituted variables, such as symmetrical components. The solution of circuit equations by the method of diagonalizing the impedance matrix is developed in the paper, and applied to the solution of the difference equations of ladder networks. An extension to systems of difference equations follows. Diagonalizing is equivalent to the use of substituted currents, voltages and impedances such that there is no mutual coupling between the substituted networks. The substituted currents are then calculated without difficulty and the original circuit currents obtained by a simple transformation. The method has the additional advantage that, since the transformation is independent of the circuit constants, it may be applied to all circuits possessing the same degree of symmetry. Ladder networks may also be solved by regarding them as a series of fourterminal passive networks. The elements of matrix algebra are included for completeness. View full abstract»

12. The Theory of the SuperRegenerative Receiver Operated in the Linear Mode
Page(s): 143  157A general theory is developed of the superregenerative receiver in the linear, as distinct from the logarithmic, mode. Two states of operation are distinguished, corresponding roughly to sinusoidal and rectangular wavequench. Formulae are derived for the properties of the receiver in both states when receiving a signal much greater than noise. The theory of the slopecontrolled state predicts that the frequency response and the envelope of the output oscillations of such a receiver will each have the shape of a Gaussian error curve. This is amply confirmed by experiment. A theory of noise in the superregenerative receiver is given according to which the whole of the noise energy collected by the r.f. acceptance band of the receiver goes to produce noise in a bandwidth equal to half the quench frequency in the receiver output. The effect of further decreasing the postdetector bandwidth is also dealt with, and the origin of noise in the superregenerative receiver itself is briefly discussed. Considerable attention is given to the output spectrum due to signal and noise as an aid to understanding the operation of the receiver. View full abstract»

13. The elements of wave propagation using the impedance concept
Page(s): 171  198The elements of propagation of radio waves are developed from the ordinary theory of transmission lines, familiar to electrical engineers, without any explicit reference to Maxwell's equations. Phenomena such as the Brewster angle, the critical angle, propagation in hollow metal pipes, reflection and transmission by wire netting, etc., are all counterparts of wellknown phenomena in the theory of transmission lines. The most powerful instrument for integrating all these phenomena into a single picture is the concept of field impedance. Just as potential difference (measured in volts) divided by current (measured in amperes) leads to the concept of circuit impedance, so electric field (measured in volts/metre) divided by magnetic field (measured in amperes/metre) leads to the concept of field impedance. Widespread use of the concept of field impedance was overdue before the war but has to some extent come into its own during the war. View full abstract»

14. The calculation of field strengths over a spherical Earth
Page(s): 325  336Curves and formulae are given for the calculation of field strength at any height and distance from the transmitter for the case of horizontallypolarized electromagnetic waves over a curved Earth or sea. Sufficiently within the optical range the field is calculated by ray theory, and appropriate quantities for calculating path difference and divergence of reflected ray are given. At exact optical cutoff the field is calculated by an approximate method believed to be accurate to 1 db, and is presented in the form of contour curves of equal field strength on a plot of receiver height against transmitter height. Sufficiently far beyond optical cutoff the field is given by the first term in the diffractionformula series. To calculate the field near optical cutoff, a curve should be drawn of field against distance for the heights of transmitter and receiver in question which joins smoothly the raytheory curve for inside optical range to the oneterm curve for the region beyond and passes through the point determined for the actual cutoff distance. The case of vertically polarized waves is also briefly discussed, and curves and formulae are given for the reflection coefficient (including surfacewave term) where ray theory is applicable, and for one term of the diffraction formula in the region well beyond optical cutoff. View full abstract»

15. The probability distributions of sinusoidal oscillations combined in random phase
Page(s): 76  86This paper discusses a fundamental problem involved in the theory of multichannel transmission. In modern carrier telephone systems a number of channels pass through common line amplifiers. The loading of these amplifiers therefore fluctuates in accordance with the sum of the speech voltages applied to the individual speech channels in the carrier group, and the maximum loading depends upon whether there can be a simultaneous occurrence of peak values in all the speech channels. In general, this is an extremely rare occurrence. As an alternative to providing speech circuits, some of the channels may, however, be subdivided to provide voicefrequency telegraph channels, the speech being then replaced by a number of singlefrequency tones. When the telegraph channels are idle, these tones are continuous and the maximum loading of any common amplifier may be increased thereby. Some modern automatic signalling systems also use continuous tones or long periods of tone for the transmission of signals, so that possible overloading of the amplifiers must again be considered. It becomes important, therefore, to be able to determine the probabilities associated with the combination of sinusoidal signals from a number of different channels, and in particular the probabilities that the instantaneous value and the length of the resultant vector will exceed certain limits. The instantaneous value of the resulting signal is, of course, the sum of the values in all the combined channels. Under suitable conditions the peaks of the instantaneous value trace out an envelope for the resulting signal, and the probabilities associated with this envelope are, in general, the same as those associated with the resultant vector. The paper discusses theoretically the probabilities associated with the instantaneous value and the length of the resultant vector obtained by combining n cosine oscillations of equal amplitude and random phase relationship. It is mainly concerned with very small v alues of n (=2, 3, 4? 12), and gives, for the first time, a complete set of curves showing the probabilities of the instantaneous value and the length of the resultant vector exceeding any given limits. For large values of n one aspect of the problem has been discussed by Rayleigh, and solutions for very large values of n have been given by Landon and more recently by Rice in connection with fluctuation noise. For the small values of n discussed here no solution has hitherto been given, but the empirical combination of speechvoltage distributions for a small number of channels has been studied in the Post Office Engineering Research Station and has been discussed in application to the design of apparatus by a number of authors. The mathematical theory used to derive the results is given in Section 6. It is hoped that this Section will be of general interest, because the underlying theories are of fundamental importance and may be capable of application to other physical problems, as, for example, when the amplitudes as well as the phases of the combined oscillations are random. While some of the formulae used are not original, as the list of references shows, they are, for convenience, collated here from the scattered memoirs in which they appear and which contain much other mathematical material extraneous to the present subject. View full abstract»

16. The parallelT bridge amplifier
Page(s): 42  51The paper discusses the design and performance of lowfrequency selective amplifiers using negative feedback through a parallelT bridge network. Two basic forms of the circuit giving symmetrical selectivity are analysed, and a method of varying the selectivity while maintaining the magnitude and frequency of the peak amplification constant is indicated. The paper concludes with a brief discussion of the problems which arise in the design of bridge amplifiers having high selectivity. View full abstract»

17. The theory of the nonlinear bridge circuit as applied to voltage stabilizers
Page(s): 16  22The paper deals with the theory and design of the nonlinear Wheatstone bridge circuits used in voltage stabilizers. It is restricted to the use of the bridge as a source of voltage proportional to the change in the supply voltage and to nonlinear elements obeying the law V = kIn, where n and k are constants. Four circuits are considered, and formulae are deduced for the general case of a resistive load across the output terminals. The effect of changes in the various parameters is discussed. Formulae are also given for the load required for maximum power output from the bridge for a given change in input voltage. The paper concludes with a review of the advantages and disadvantages of the various circuits. View full abstract»

18. An anticlutter radar receiver
Page(s): 459  465One of the major limitations to the efficacy of radar is the presence of responses from land, sea or rainstorms in the vicinity of a target, such responses being generally known as Â¿clutter.Â¿ If the clutter is of amplitude greater than the targetecho, detection of the echo is very difficult; in many cases, however, the clutter is of amplitude smaller than the targetecho, but the latter is lost owing to saturation of the receiver or display equipment by the clutter. It is shown, both theoretically and practically, that such loss can be prevented in the cases of sea and rain clutter by the use of a receiver, the amplification characteristic of which is such that the amplitude of an output signal is proportional to the logarithm of the amplitude of the corresponding input signal; in the case of land clutter, loss is not necessarily prevented, but the probability of such loss is reduced. A logarithmic receiver compresses input signals of any strength less than 100 db above the mean noise power, into output signals of voltage less than four times the outputnoise deviation voltage, with negligible change in the detectability of small signals compared with the use of a linear receiver. In addition, with such a receiver, the difference in voltage of two output signals depends only on the ratio of the corresponding input signals, and not on their absolute amplitudes. These properties make a logarithmic receiver superior to a linear receiver for a number of subsidiary applications, some examples being given in the paper. View full abstract»

19. New methods for locating cable faults, particularly on highfrequency cables
Page(s): 385  395Normal faultlocating procedures become impractical in certain conditions, either for purely technical reasons or on account of the loss of service time involved. This paper commences by summarizing a theoretical investigation of the possibilities of applying pulse and frequencymodulation methods to this problem on wideband coaxial telephone cables. A practical faultlocator employing d.c. pulses is then described. The problem is first contrasted with that of radar, and the factors controlling the choice of the transmitted waveform and those limiting the accuracy of location attainable are then discussed. The fundamental requirements of a frequencymodulation system are examined in some detail, and it is concluded that, although an f.m. instrument would be attractive in certain circumstances, the practical advantage lies with the pulse type of faultlocator owing to the clarity and reliability of its indications when more than one fault is present. The d.c.pulse instrument described has been in use for some time, and faults on coaxial cables have been located within 1% of their true distances at ranges up to 10 miles. View full abstract»

20. Resonance Methods of Dielectric Measurement at Centimetre Wavelengths
Page(s): 53  68The paper deals with the theory and experimental development of resonator systems suitable for measurement of the permittivity and power factor of solid dielectric materials in the wavelength range below 50 cm (600 Mc/s). The relative suitability of three forms of resonator, namely a shortcircuited length of coaxial transmission line operating in the principal mode, and hollow cylindrical cavityresonators operating respectively in the E010 and H01n modes, is discussed. The theory governing the resonant behaviour of these systems when wholly and partially filled with Â¿lossyÂ¿ dielectric is developed, leading to relations connecting the permittivity and power factor of the latter with the resonant wavelength and Qfactor respectively. View full abstract»

21. Frequency modulation
Page(s): 197  213Frequency modulation is likely to play an important part in postwar radio developments. The present position of this method of communication is here reviewed; a brief discussion of the features of the three methods of modulationÂ¿amplitude, frequency and phaseÂ¿is followed by a survey of the history of frequency modulation, with a consideration of its limitations, advantages and present applications. The first of the two main Sections of the paper is concerned with the production of a frequencymodulated signal; direct and indirect (integrated phasemodulation) methods are examined with particular reference to the variablereactance valve modulator with automatic meanfrequency correction, and the indirect transposedsideband modulator with a crystalcontrolled master oscillator. Measuring and monitoring equipment is also described. The second main Section deals with frequencymodulated reception, and indicates the essential features of a frequencymodulated receiver, which, except for the amplitude limiter and frequencytoamplitude converter (examined in detail), is similar to its ultrashortwave counterpart for amplitude modulation. Also included are three Subsections dealing with tuning indicators, frequencydeviation compression, and distortion and interference. Possible future developments are discussed, and the paper concludes with a bibliography of the most important contributions to the literature of frequency modulation made over the past twenty years. View full abstract»

22. The field of a coil between two parallel metal sheets
Page(s): 78  84This paper solves the problem of a circular coil of any radius with its plane parallel to two infinite and perfectly conducting planes separated by any distance. It is shown that if the distance between the planes is less than half a wavelength, then the output of work from the coil is zero; this corresponds to the wellknown Â¿cut off propertyÂ¿ of the more conventional form of wave guide. The radiation resistance per unit arc of a singleturn coil is found to fluctuate, according to the radius of the coil, between zero and twice the resistance per unit length of a straight wire between the same planes. Equation (12) of the paper gives an exact expression for the field when the sheets are close together, and thus gives the absolute calibration for an Â¿attenuatorÂ¿ of this form: also the parameters are calculated for a current transformer consisting of a pair of concentric circles between metal sheets. The solution is attempted for a single turn surrounding a metal tube (such as a steel mast): this succeeds formally and a numerical solution in any particular case is feasible. It may thus be said to have solved the two extreme cases of a circular girdle round a biconical metal sheet, a problem whose general solution remains very cumbersome so far. A particular form of solution of great practical interest is a coil enclosed in a cylindrical screeningcan with closed ends. This solution turns out to be simple, and by its help the extensive experimental work of Mr. A. G. Bogle can now be completed analytically and extended to cover the change of highfrequency resistance of a coil due to enclosing it in a screen. View full abstract»

23. The development of polythene as a highfrequency dielectric
Page(s): 23  31The paper is mainly concerned with the power factor of polythene (the high polymer of ethylene), which, being normally of the order of 0.000150.0003, renders the material highly suitable as a highfrequency dielectric. It has been found, however, that oxidation may occur during the processing of the material in the manufacture of cables and mouldings, and that this increases the power factor and may also lead to difficulties in extrusion. These effects may be virtually eliminated, however, by the use of small amounts of antioxidants. The measurable, albeit low, power factor of pure polythene is hardly concordant with the supposedly nonpolar nature of the substance, and a number of possible explanations of the small basic power factor have been investigated. Measurements of power factor over wide frequency and temperature ranges show that its variation for pure polythene is extremely sluggish, but that oxidation causes the appearance of marked peaks; these observations are examined in the light of present theories of dipole loss. A brief account is given of the structure of polythene, and of its main physical and mechanical properties. View full abstract»

24. Some sources of error in microwave milliwattmeters
Page(s): 229  238An approximate analysis is made of the factors that influence the intrinsic accuracy of a heated filament used as a transfer device for measuring power at microwavelengths in terms of a lowfrequency calibration. It is shown that instruments incorporating such filaments are usually subject to errors of significant magnitude if the filaments are longer than about onetenth of a wavelength, and that the errors are usually smaller in resistance milliwattmeters than in thermocouple instruments used in similar conditions. Experiments are described which show that serious errors, due to the inefficiency of the transformer used to match the power source to the filament of the instrument, can occur in addition to those described in the analysis. It is concluded that filament instruments cannot, in the present state of development, be relied on as standard transfer instruments for measuring microwave power in terms of a lowfrequency calibration. View full abstract»

25. A Theory of Valve and Circuit Noise
Page(s): 45  52The paper presents a fundamental theory of noise which the authors believe to be physically perspicuous and from which all the wellestablished formulae used in practice can be deduced by direct mathematical argument. Since these formulae almost all relate to meansquare noise in linear circuits, the theory will not be applied here to other problems, although its ideas are valuable in attacking more complicated problems. The subject is discussed under the following heads: (1) Introduction; (2) the basic postulate and the fundamental equations; (3) the Â¿mean theoremÂ¿ and the Â¿meansquare theroemÂ¿ (4) the calculation of meansquare noise; (5) thermal noise; (6) application to valve and circuit noise; (7) spacecharge effects; and (8) transittime effects. View full abstract»

26. Field distributions near a centrefed halfwave radiating slot
Page(s): 282  289The paper describes the methods and results of experiments made to map out the electromagnetic fields associated with a slot radiator. The radiator was a narrow slot about half a wavelength long cut in a large circular metal sheet of diameter about 9 wavelengths. The results include the relative magnitudes and phases of the electric vector over a quadrant of the metal sheet close to the slot, the relative magnitudes of the magnetic vector along the axes of the slot, and also some polar diagrams of radiation at relatively large distances from the slot, both on and off the sheet. The results obtained are correlated as well as possible with the theoretical expressions for the fields associated with a halfwave slot of infinitesimal width in a sheet of infinite extent. These theoretical expressions are derived from the usual formulae for the fields of a thin dipole by the use of an extension of Babinet's principle recently described by Booker. View full abstract»

27. Calculation of the Electromagnetic Field, Frequency and Circuit Parameters of HighFrequency Resonator Cavities
Page(s): 335  343A method for the calculation of the field components of free electromagnetic oscillations in metal cavities of any shape is described with reference to Klystron resonators. Whereas in a previous paper a method for computing solutions of Laplace's equations was given, the present paper is concerned with the wave equation Â¿Â¿ + (Â¿2/c2)Â¿=0. Again, the differential equation is replaced by a system of difference equations, which in the case of free vibrations are homogeneous and soluble only for certain values of the parameter Â¿2/c2, the proper values. A method for finding the lowest value of Â¿2/c2 without solving a determinantal equation is described. The boundary of Klystron resonators contains sharp corners, often feather edges, which present a special problem. In order to obtain the necessary accuracy for the circuit parameters, with a reasonable amount of computation work, it is essential to take account of the analytic behaviour of the fields near sharp corners. This is done in a manner which is particularly well suited to the relaxation method of solution of the equations, and a great deal of computation work is thereby saved. Once the field components and the resonant frequency are found, the beam impedance and the damping constant are easily determined. View full abstract»

28. Some Applications of Field Plotting
Page(s): 275  293By the process of fieldplotting in the crosssection of a uniform transmission line, an orthogonal field pattern of curvilinear squares satisfying the boundary conditions is obtained. If Nv is a number of voltage steps and Nf the number of electrostatic flux lines in this field plot, the characteristic impedance is given by Z = 377Nv/NfÂ¿Â¿/k where Â¿ is the permeability, and K is the permittivity. Applications to coupling and screening are also considered. The use of models in an electrolytic tank for capacitance determination from field plots or direct measurement is discussed, and an axially symmetrical threedimensional field is plotted. Mention is made of the relaxation process and rubbersheet methods of fieldplotting. View full abstract»

29. Spacecharge effects in beam tetrodes and other valves
Page(s): 17  24The space charge in the screenanode space of a beam tetrode is examined, taking into account the effect of electrons returned from the virtual cathode into the region between the grid and cathode. As with previous investigations which do not take into account the effect of the returned electrons in the cathodegrid space, it is found that over a range of anode voltages just below the knee, three solutions of the problem satisfy Newton's laws of motion for the electrons and also Poisson's equation for the charge distributions. Two of these solutions give rise to discontinuities in the characteristic. The third, however, is continuous for all anode voltages from zero up to the knee, and corresponds closely to experiments on actual valves. In it, a virtual cathode which remains at a fixed point between the screen and the anode is set up. The question arises, What property of this solution determines its correspondence with experiment? It is found that Maupertuis's principle of least action, as an integral of momentum with respect to distance, can be applied. The principle of least action as it stands cannot, however, be applied to a single arbitrarily chosen electron, but by calculating the action per unit of time, it can be applied to all three solutions, whether electrons are reflected or not. This leads to the conclusion that the action per unit of time is least for the third solution. Since this corresponds to the conditions observed experimentally, it is asserted that, in problems concerned with the motion of charged particles in which more than one consistent solution can be found, the actual state set up will be that for which the action per second is least. A simple theory of the effect of perturbations of the spacecharge density, due, for example, to the random fluctuations of the cathode emission, is developed. The rate of growth of a perturbation depends on its size, and if it is small, it is unlikely to grow to such an extent, before being swept to the anode, as to cause instability of a particular charge distribution. It is concluded that such perturbations do not form an alternative explanation of the fact that the state containing the virtual cathode is always that set up. The growth of the perturbations is shown to depend on whether the anode potential remains constant or can vary during the passage of a perturbation. It is concluded that the theory of the fluctuations of a spacechargelimited current cannot be dealt with accurately on the assumption that the fluctuation current is independent of the anode load. Finally, the fluctuations of the spacechargelimited current in diodes and triodes is described on the basis of the given theory of perturbations. For identical spacecharge conditions near the cathode, the diode has a planar electric field which exercises no electronoptical action, while the triode has a strong focusing action in the space between grid and cathode. The conclusion, that the perturbations can grow to a greater extent in diodes than in triodes, agrees with the experimental results on the noise of diode and triode valves. View full abstract»

30. Tuning devices for broadcast radio receivers
Page(s): 405  423The wide choice of entertainment provided by the broadcast receiver is perhaps its most important feature, and the development of tuning devices to simplify the exercise of that choice has played an outstanding part in radio receiver design. Both station selection and ready identification of a programme found by random searching are involved. The paper opens with a brief historical review of tuningdevice evolution from the introduction of singleknob tuning to the immediate prewar designs. Listening tests are used to establish the degree of mistuning to cause observable deterioration of quality, and to suggest a target design tolerance for tuning errors. A consideration of frequency stability on the broadcast bands leads to an analysis of design limitations and establishes preset tuning on medium and long waves and bandspread tuning on short waves as important problems. The design of preset tuning devices is reviewed, together with their power drive and remote control, and the development of bandspread tuning is described, together with the associated receiver circuits. Appendices give the measured frequency response and harmoniccontent characteristics of the receiver used in the listening tests, together with a mathematical analysis of these characteristics as derived from the intermediatefrequency response. View full abstract»

31. The Development and Study of a Practical SpacedLoop Radio DirectionFinder for High Frequencies
This paper discusses the principles of design of spacedloop radio directionfinders and describes a practical instrument embodying these principles. The dimensions of the model described are: size of loops, 1 m square; spacing between loops, 3 m. It has been designed for the frequency range within which the spacedloop directionfinder can have most useful applications, namely 3Â¿15 Mc/s (Â¿ 20Â¿100m). The sensitivity of the instrument is such that for an arc of silence not exceeding Â±5 deg, the required field strength, for a ground wave, varies from 1.5 to 4 Â¿V/m throughout the range. The directionfinder is provided with a simple and effective means of determining the sense of the bearing, operating on novel principles. To obtain the high accuracy of which the spacedloop radio directionfinder is capable, care must be taken that the local surroundings of the aerials do not contain features capable of introducing errors of various types. In particular, attention must be paid to the proper disposition of power or telephone cables. In the Appendices, the effects of the essentially nonuniform character of the current distribution in loop aerials are considered, and it is shown that certain arrangements of spacedloop aerials may be very inaccurate on account of a type of polarization error thus introduced. View full abstract»

32. Some Considerations in the Design of WideBand RadioFrequency Amplifiers
Page(s): 237  246The object of this paper is to review some of the theoretical considerations and design requirements of wideband radiofrequency amplifiers for television, radar and similar applications. In order to keep the paper within reasonable bounds, great detail in the various Sections has not been attempted. For instance, Section 4.3 on Bandwidth, including the design of intervalve couplings, could easily be amplified to the status of a complete paper. A number of papers on intervalve couplings have been published, and others will undoubtedly be published in the near future; a great deal has also been written about noise in radio receivers and about detection: only the features which have special significance in television amplifiers have therefore been surveyed. View full abstract»

33. The design and operation of highpower broadcast transmitter units with their outputs combined in parallel
Page(s): 183  198The paper describes a method, developed by the British Broadcasting Corporation, of obtaining very large r.f. output power for broadcasting purposes by combining the outputs of two or more similar transmitter units. The principle is analogous to paralleling the outputs of a number of a.c. generators, with the difference that, in the case of transmitters, the frequency of the separate units is identical, the variables being phase and loading. The method of ensuring equality of the r.f. output voltage and modulation amplitude of the separate transmitter units is described. The circuits for combining and matching a variable number of transmitters to a common load are detailed, and a number of special aspects relating to the design of transmitters for parallel operation, including the principle of Â¿drive suppressionÂ¿ for protection purposes, are discussed. The design of the circuits and operational procedure developed for the Droitwich highpower mediumwave station, which has a power output to the aerial of 400 kW carrier provided by two 200kW class B modulated transmitters in parallel, are described together with operating experience. Mention is made of a second station, the Ottringham highpower longwave station of the B.B.C. European service, in which an aerial power of 800 kW was obtained by means of four similar 200kW transmitters operated in parallel, and which will be fully described in another paper. Appendices contain some data on the design of the modulatedamplifier output circuit of the transmitters used, and a description of an r.f. impedance monitor for fault protection on the highpower r.f. chain. View full abstract»

34. NonLinear Distortion in Transmission Systems
Page(s): 45  56The problem of the distortion noise generated by a signal in its transmission through one or more nonlinear devices is analysed. This subject has become of increasing importance in connection with the development of the transmission of different types of signals on a multichannel basis through a common network, e.g. modulator, amplifier or transmitter. The provision of such networks is now of frequent occurrence, and in order that economic and satisfactory designs may be obtained it is essential to be able to determine precisely the effect of nonlinearity and also the limiting linearity requirements, preferably in a form which can be readily comprehended and applied by designers. The problem has been considered to be very complex, and existing literature is both scanty and involved. This paper presents a simple solution, which is capable, in general, of immediate application to any type of complex signal (e.g. speech, music, television, voicefrequency telegraphy or thermal noise) covering any frequency band or frequency allocation. The results are presented to the designer in the form of the limiting levels of the various harmonics of a single tone, which levels must not be exceeded if the noise power from the nonlinear device in any specified frequency band is not to exceed a predetermined value. The differences in the linearity requirements of a single amplifier and of a repeatered system are demonstrated. Provided the input/output characteristic of the network can be expressed as a singlevalued power series independent of the frequency in the working band, the results obtained should cover with adequate accuracy the design of all types of transmission systems. View full abstract»

35. Highfrequency electrical breakdown phenomena in gases
First Page of the ArticleView full abstract» 
36. Input impedances of centrefed slot aerials near halfwave resonance
Page(s): 290  294Slot radiators of various widths were fed via balanced parallelrod transmission lines connected near the centre points of opposite edges of the slots. Series components of impedance at the feed points were measured for each slot at a number of frequencies, including that at which the length of the slot was Â¿Â¿. In the first set of experiments the slot was free to radiate on both sides of the metal sheet in which it was cut. Further measurements are described in which the dimensions of the slot were kept constant whilst rectangular cavities of various dimensions were placed symmetrically behind the slot so as to prevent radiation from one face of the metal sheet. View full abstract»

37. Vector Permeability
Page(s): 407  414The principal magnetic properties of transformer core materials are generally expressed in terms of permeability and power loss per kilogramme. Another method, described in this paper, is to assign a complex value to the permeability (Sections 2 to 4). For many purposes this method possesses advantages; for example, very simple relations can be found (Sections 5 to 7) connecting the electrical characteristics of coils with the components of the vector permeability of their cores. Data for samples of nickeliron and siliconsteel are given (Section 8) and, by way of an example of the use of the system, a simple method of securing the optimum design for a lowloss reactor is worked out (Section 9). View full abstract»

38. The electrical properties of saltwater solutions over the frequency range 1Â¿4000 Mc/s
Page(s): 69  75The paper describes a series of measurements on solutions of sodium chloride in distilled water over the frequency ranges 0.9513 and 6904 320 Mc/s. The results are discussed in terms of the DebyeFalkenhagen theory of electrolytes and of the available data on the absorption band exhibited by water in the region of 10 000 Mc/s (wavelength 3 cm). A comparison is made with the published results on the electrical properties of seawaterÂ¿for frequencies up to 10 Mc/sÂ¿and deductions are made as to its probable behaviour at very high frequencies. View full abstract»

39. The calculation of rectifier and inverter performance characteristics
Page(s): 130  131First Page of the ArticleView full abstract» 
40. An Improvement in EndFire Arrays
Page(s): 415  418A conventional endfire array has a linear phase change of 360Â° per wavelength along it, and a uniform amplitude distribution. This paper describes how gain improvement and sidelobe reduction can be obtained by arranging for a greater phase change than this, and at the same time tapering the amplitude distribution. View full abstract»
Aims & Scope
The Journal of the Institution of Electrical Engineers  Part III: Radio and Communication Engineering was published by the IET between 1945 and 1948.