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

Some aspects of the design of balanced rectifier modulators for precision applications
Jan29 2010 
Radio standards
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Discussion on Â¿Notes on the stability of LC oscillatorsÂ¿ before the Cambridge Radio Group, 29th October, 1945
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Spacecharge effects in beam tetrodes and other valves
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Discussion on Â¿Threedimensional cathoderay tube displaysÂ¿ before the Radio Section, 24th March, 1948
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Theory of communication. Part 1: The analysis of information
Jan29 2010 
The Electrical Constants of a Material Loaded with Spherical Particles
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Theory of communication. Part 2: The analysis of hearing
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Theory of communication. Part 3: Frequency compression and expansion
Jan29 2010 
An introduction to hyperbolic navigation, with particular reference to Loran
Jan29 2010
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1. Theory of communication. Part 1: The analysis of information
Publication Year: 1946 , Page(s): 429  441
Cited by: Papers (31)Hitherto 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»

2. The Electrical Constants of a Material Loaded with Spherical Particles
Publication Year: 1947 , 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»

3. Theory of communication. Part 2: The analysis of hearing
Publication Year: 1946 , 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»

4. Theory of communication. Part 3: Frequency compression and expansion
Publication Year: 1946 , Page(s): 445  457
Cited by: Papers (2)It 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»

5. An introduction to hyperbolic navigation, with particular reference to Loran
Publication Year: 1946 , Page(s): 243  245First Page of the ArticleView full abstract» 
6. The Theoretical Precision with which an Arbitrary RadiationPattern may be Obtained from a Source of Finite Size
Publication Year: 1948 , 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»

7. The propagation of electric waves in a rectangular wave guide
Publication Year: 1945This 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»

8. The calculation of field strengths over a spherical Earth
Publication Year: 1947 , 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»

9. Frequency modulation
Publication Year: 1945 , 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»

10. The Theory of the SuperRegenerative Receiver Operated in the Linear Mode
Publication Year: 1948 , 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»

11. Resonance Methods of Dielectric Measurement at Centimetre Wavelengths
Publication Year: 1946 , 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»

12. The design of a highfidelity disc recording equipment
Publication Year: 1947 , Page(s): 275  295Section 1 of this paper outlines the present technique of disc recording and indicates briefly its principal advantages and disadvantages as compared with other systems of sound recording. Present practice and the existing degree of standardization are discussed as regards cutting speed, turntable speed, groove shape, groove spacing and disc dimensions. The magnitudes of the stylus amplitudes, velocities and accelerations normally involved are shown, and the considerations which govern the use of radius compensation and the choice of the optimum recording characteristic are discussed. Section 2 deals in a little more detail with some of the technical problems which were encountered in developing a highfidelity disc recording equipment. The turntable drive and the various considerations which arise in mounting the cutter head are discussed. The design of a robust, highfidelity cutter head is described and methods of making cue marks and of removing swarf while recording are outlined. A practical method of obtaining the required radius compensation is also discussed. Section 3 describes a highfidelity disc recording equipment, and indicates the performance that may be obtained from it. View full abstract»

13. The Fundamental Principles of Frequency Modulation
Publication Year: 1946 , Page(s): 153  158
Cited by: Papers (30)First Page of the ArticleView full abstract» 
14. The probability distributions of sinusoidal oscillations combined in random phase
Publication Year: 1946 , 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»

15. Forced oscillations in oscillator circuits, and the synchronization of oscillators
Publication Year: 1945 , Page(s): 226  234
Cited by: Papers (1)The behaviour of a feedback oscillator circuit under the influence of an injected tone having a frequency close to the natural frequency of oscillation is considered from the point of view of the steadystate equilibrium of the loop transmission circuit. The conditions for the absence or suppression of the free oscillation and for the stability of the forced oscillation are found. The application of the principles to certain common types of oscillator is discussed, and the effect of impurities in the injected tone is outlined. View full abstract»

16. The measured performance of horizontal dipole transmitting arrays
Publication Year: 1945 , Page(s): 68  79Measurements of the performance of horizontal dipole arrays are described, and are compared with the theoretical performance under ideal conditions. The measurements include polar diagrams, the effect of ground slope and radiation through other arrays, and the performance over a frequency band of ?2% relative to the design frequency, which is typical of the width of existing shortwave broadcasting bands. One method of measurement consisted in elevating a calibrated frame receiving aerial using a captive balloon; by varying the height and position of the balloon, the field strengths in different directions from the array were measured. In the second method a frame aerial at ground level was used; this gave only relative values of field strength and was used mainly to determine the frequency characteristic. It was found that for an array radiating over a flat site free from obstacles there was good agreement between the theoretical and measured performance; the maximum field strength was of the order of 0.8?0.9 of the theoretical value. A sloping site or radiation through other nearby arrays, however, may cause appreciable departures from the theoretical characteristics. An array having no reflector curtain covers the frequency band of ?2% without appreciable loss in radiation efficiency. This is also true for an array with a parasitic reflector curtain which is tuned to the working frequency. If, however, the reflector is tuned always to the midband frequency, the radiation efficiency at other frequencies is reduced. The bandwidth can be increased by reducing the characteristic impedance of the dipoles, and measurements have been made on two types, one consisting of single wires and the other of two parallel wires spaced 6 in apart. For an array of four rows of singlewire dipoles, the bandwidth is ?1% for a 10% drop in field strength relative to the midband frequency; for a similar array of twowire dipoles the corresponding bandwidth is ?2%. The bandwidth o f arrays containing less than four rows is approximately the same. View full abstract»

17. An Improvement in EndFire Arrays
Publication Year: 1947 , Page(s): 415  418
Cited by: Papers (4)A 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»

18. Matrix Methods in the Solution of Ladder Networks
Publication Year: 1948 , 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»

19. An anticlutter radar receiver
Publication Year: 1948 , 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»

20. The elements of wave propagation using the impedance concept
Publication Year: 1947 , 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»

21. A method of transmitting sound on the vision carrier of a television system
Publication Year: 1946 , Page(s): 251  267The paper describes a television system in which sound pulses having a constant height and variable width are inserted in the line synchronizing periods. It is claimed that this method of transmission leads to a simplified receiver and that the programme quality is better in the presence of severe interference. Other advantages are that the frequency bandwidth for transmission is reduced; the method of receiving sound ensures automatic volume control; the sound pulses provide a fixed reference level for automatic volume control on the vision channel; mutual interference between vision and sound often present on twochannel reception is avoided; reduced transmission bandwidth simplifies the design of the receiving antenna; mutual coupling between the vision and sound antennae at the transmitter is avoided; and the installation and maintenance costs of the sound transmitter are saved. The frequency range of the system operated in conjunction with the prewar British transmission would be limited to 5 kc/s. View full abstract»

22. The SuperRegenerative Detector: an Analytical and Experimental Investigation
Publication Year: 1946 , Page(s): 23  28On the basis of an exponential buildup of oscillations in its grid circuit, the superregenerative phenomenon is analysed and a general expression for the output at modulation frequency is obtained. This expression is examined term by term and reveals the mechanism of (a) high amplification, (b) selfa.v.c. action, (c) excessive distortion of the modulation frequency at modulation depths in excess of 50%. All these properties are quite characteristic of the superregenerative detector in practical operation. Histograms illustrate the distortion effect in terms of modulation depth. Various oscillograms verify the mathematical results, particularly in regard to the law of buildup of oscillations as a function of the amplitude of the applied signal. The dependence of radiofrequency selectivity and modulationfrequency gain upon the quenching frequency is shown in the analysis and verified by measurements. It is shown that an optimum quenching frequency exists for maximum gain at the modulation frequency. If this optimum frequency is slightly exceeded, the noise background may be removed without severe reduction of gain. The ability of the superregenerative detector to discriminate agamst impulsive radiofrequency interference (e.g. motorvehicle igmtion interference) is analysed briefly. The reception of frequencymodulated signals is also discussed briefly. View full abstract»

23. Some aspects of the design of balanced rectifier modulators for precision applications
Publication Year: 1948 , 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»

24. Television broadcasting practice in AmericaÂ¿1927 to 1944
Publication Year: 1945 , Page(s): 145  160This paper reviews the history of television broadcasting in America from 1927 to the present, with particular emphasis on current practice. Section 1, the historical survey, traces the evolution of standards of transmission, frequency allocations, and broadcasting practice. Noteworthy programmes are recalled. Section 2, on present practice, gives a detailed account of the standards of transmission governing public broadcasting under the current regulations of the Federal Communications Commission. The stations currently operating are listed. Typical equipment used in these stations is described in four categories: studio equipment, transmitters, radiators, and mobile pickup equipment. The design of current (i.e. immediately prewar) receiving equipment is described. The paper concludes with a digest of postwar prospects. View full abstract»

25. Threedimensional cathoderay tube displays
Publication Year: 1948 , Page(s): 371  387The display of threedimensional information is considered with particular reference to a radar system in which a narrow pulsed beam of radiofrequency energy is used to explore automatically a volume of space. The threedimensional displays are used to display the positions of the reflected Â¿signalsÂ¿ with respect to the three coordinates of the volume, in order that the radar can be used as an objectdetecting and locating system in three dimensions. In the past, Â¿configurationalÂ¿ methods have been used, wherein the shape of the intensitymodulated echotrace on the cathoderay tube is altered to add a third variable to the two already provided by the c.r.t. deflections. These types are not discussed, attention being concentrated on other methods. The Â¿truly threedimensional displaysÂ¿ utilize a mechanical motion to add a third dimension to the screen of the cathoderay tube, the picture appearing as an actual volume. The Â¿perspective displaysÂ¿ simulate the same picture as in the previous display without any moving mechanisms, rotation of the volume and/or stereoscopy being used to give the impression of three dimensions. The Â¿oblique displaysÂ¿ obtain the required three coordinates by combinations of two or more twocoordinate pictures on the same cathoderay tube. The Â¿polychromatic displaysÂ¿ use colour to represent a spatial coordinate. The physiological and psychological problems of the human operator peculiar to threedimensional displays are discussed, and a Section is included on the relative advantages of Â¿trueÂ¿ and Â¿relativeÂ¿ displays. Another Section on Â¿display sensitivityÂ¿ leads to the general theoretical considerations involved in threedimensional displays. The application of threedimensional displays to other fields, for example Xray photography, is briefly discussed. The revised form of the radar equation for use with threedimensional displays is given in an Appendix. View full abstract»

26. Radiation from Large Circular Loops
Publication Year: 1946 , Page(s): 345  351In this paper is calculated the radiation resistance of a circular loop of any radius and also its polar diagram of electric field at a large distance. It is shown that, according to the radius, the field can be zero in the equatorial plane or at any angle of elevation. It is shown that the Â¿highangleÂ¿ radiation can be sensibly removed by using two concentric and coplanar loops having suitably chosen radii: but with this disposition the current must be supplied to both loops and it is impracticable to induce one current from the other. The Â¿highangleÂ¿ radiation can also be much reduced by the use of two similar coaxial large loops in parallel planes, and this offers a disposition which may be useful in practice. The power gain of a stack of N similar small loops is shown to be equal numerically to the gain of an Nmember inline array of electric doublets; and it can be shown that this is true whatever the radius of the loop, but one or more side lobes can be sensibly obliterated by suitable choice of this radius. Having regard to the difficulties of Â¿feeding,Â¿ inherent in the construction of all aerial systems, it would seem that a pair of parallel large loops is one of the simplest systems for obtaining a horizontal electric field concentrated mainly in a zone of about Â± 30Â° from the equator. The choice between two such loops and a stack of small loops depends very much on the wavelength to be used. View full abstract»

27. Highfrequency electrical breakdown phenomena in gases
Publication Year: 1948First Page of the ArticleView full abstract» 
28. The design and use of radiofrequency openwire transmission lines and switchgear for broadcasting systems
Publication Year: 1946 , Page(s): 191  206The paper describes the various types of transmission lines in use at transmitting stations of the British Broadcasting Corporation, their impedance, attenuation and powercarrying characteristics, together with results of various tests, general details of construction, and methods of matching the load to the transmission line. The major part of the work described was carried out before the end of 1943. The paper is written primarily from the point of view of the engineer engaged on design and practical work in the field. Data are included enabling the most suitable transmission line for any practical purpose to be designed. The range of frequencies considered is from 0.2 to 25 Mc/s; of this range those up to 2 Mc/s are considered as medium waves and those from 2 Mc/s to 25 Mc/s as short waves. View full abstract»

29. Circle diagrams of impedance or admittance for fourterminal networks
Publication Year: 1948 , Page(s): 243  252The paper offers a theory of circle diagrams of impedance or admittance representing the relations between terminal impedances and input impedances for the general passive fourterminal network, including the cases of asymmetry and dissipation, so formulated that common transmissionline diagrams become special cases. After a review of earlier work on the subject, the relations between terminal and input impedances are expressed in terms of the iterative quantities of the network in a circle diagram. It is shown that this diagram is actually a graphical representation of the complex hyperbolic tangent function. Special circle diagrams are discussed corresponding to a nondissipative network in the stopband or passband, or at the cutoff frequency. These diagrams are studied by the application of projective geometry. An inversion of the ordinary circle diagram leads to the Smith diagram, which is described for both real and complex iterative impedances. It is pointed out that for a transmission line of less than Â¿Â¿ the error resulting from considering Z a pure resistance is of the same order of magnitude as that which would result from neglecting the damping. View full abstract»

30. Theory and performance of corner reflectors for aerials
Publication Year: 1945 , Page(s): 58  67The paper opens by arguing that the problem of constructing a highly directive aerial system is dominated by the difficulty of providing the necessary feeding cables. Continuous reflecting sheets are used as a device for reducing the number of such cables. A construction which readily suggests itself is a pair of sheets inclined to one another to form a V, with a single aerial on the bisector, more especially because the field would be known everywhere if the sheets extended to infinity. For the field of an aerial in a V can be calculated by image treatment, and an algebraic formula for the diffraction pattern can be found when the angle of the V is a proper fraction of 180?. It is shown that such algebraic expression can be expanded in a Fourier series which has the same form for all angles of the V and has coefficients which are the Bessel functions JN, J3N, J5N, etc. It follows at once from this expansion that the ideal pattern must be indistinguishable from a simple sine curve unless the circumferential width across the V at the aerial exceeds ??, and will not differ appreciably from a sine curve unless this width is verging on 3?/2. Recognition of this general condition is very valuable in practice and saves much wasted effort in laborious computation. A numerical example illustrates the convenience of the Fourier series for evaluating the pattern when the aerial is sufficiently distant from the apex to make the main beam much sharper than a sinusoid, and concurrently to produce side lobes. The second part of the paper describes an experimental investigation, at a wavelength of about 1.25 m, of the equatorial pattern produced by a halfwave aerial on the bisector of a V formed by two sheets, 3?/2 high and about 2? wide, inclined at 90?, 60? or 45?. The purpose of the experiments was to compare the observed pattern with the ?ideal pattern? appropriate to infinite sheets: they are restricted to the range in which the ideal pattern differs insensibly from a simple sinusoid. Sheets 2? wide produce a beam narrower than the ideal when inclined at 90?, and wider than the ideal when inclined at 60?. If the sheets are 2? wide then the best angle between them is about 60?. Experiment shows the pattern is not modified appreciably if the apex of the V is amputated and the resulting hole closed by a flat sheet. Such an amputation affords a saving of space and also shows that the pattern is insensitive to the shape of the back of the reflector: therefore it is not necessary to construct V reflectors to close tolerances of manufacture. Moreover, the optical concept of the advantage of a concave mirror does not apply when the source is distant only some ?? from it. Experiment shows that the pattern is affected insensibly by replacing continuous sheets by wire netting whose mesh has a side of about ?/40. Experiment also shows that the continuous sheets can be replaced by a comb of open rods, about ?? long, without appreciable detriment to the pattern. A blunt resonance effect occurs when the frequency is such as to make the rods precisely ?? long, but such as it is this resonance is undesirable. The distribution of current in a flat reflecting sheet is solved analytically in Appendix 11.1. View full abstract»

31. The design and use of resonant cavity wavemeters for spectrum measurements of pulsed transmitters at wavelengths near 10 cm
Publication Year: 1948 , Page(s): 473  484Resonant cavities have been used to measure the frequency and check the performance of radar transmitters. The object of this paper is to describe the factors influencing the design of such cavities to cover frequency bands near 3000 Mc/s, and to estimate their accuracy in the measurement of both the mean frequency of the transmitter output and its spectral distribution about the mean. The principles described are of general application to the design and use of cavity wavemeters of high discrimination. View full abstract»

32. Vector Permeability
Publication Year: 1947 , Page(s): 407  414
Cited by: Papers (2)The 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»

33. The field of a coil between two parallel metal sheets
Publication Year: 1947 , 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»

34. A Theory of Valve and Circuit Noise
Publication Year: 1946 , 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»

35. The design of electromagnetic radiogoniometers for use in mediumfrequency directionfinding
Publication Year: 1947 , Page(s): 69  77It is well known that radiogoniometers of accepted design possess inherent errors due to the coupling between the searchcoil and the fieldcoil windings, and that the magnitude of these errors increases with an increase of this coupling. In practical design it has therefore been usual to effect a compromise between the tightness of the coupling and the permissible errors. A special study of the subject has therefore been made with the object of analysing the causes of these errors and of introducing modifications which, while providing a tighter degree of coupling to the search coil, will at the same time reduce the magnitude of the instrumental errors. A preliminary examination of the various existing types of radiogoniometer shows that the errors are not uniformly Â¿octantalÂ¿ in form, and that the value of the maximum error is not necessarily directly proportional to the tightness of the coupling. Several methods of measuring the instrumental errors are described, and further information regarding the causes of apparently nonsymmetrical errors is recorded. These are shown to be due to the vector addition of a number of separate errors all harmonically related in frequency but differing in phase relationship. A final summary, in tabulated form, shows the more important results obtained at various stages during the development of a new design of radiogoniometer which is evolved and shown to be at least 6 db better in signal/noise ratio than any existing design, while at the same time possessing a maximum instrumental error of less than Â±Â¿Â°. View full abstract»

36. Forced oscillations in nearly sinusoidal systems
Publication Year: 1948 , Page(s): 88  96A large class of radio circuits which are analytically equivalent to an oscillatory network in parallel with a nonlinear negative resistance, are represented fairly accurately by the differential equation vÂ¿ Â¿ (Â¿+ÃvÂ¿Â¿v2)v + Â¿2v = EÂ¿21 sinÂ¿1t where, Â¿/Â¿, Ã/Â¿, Â¿/Â¿ are small. The behaviour of the solutions of this equation near resonance has been discussed by Appleton, van der Pol and others. The paper contains a more complete discussion of the synchronized and quasiperiodic solutions near resonance, their phases, amplitudes and energy, and also the way in which one type of stable solution gives way to another as the parameters of the system vary, for instance as the electromotive force or detuning vary. It is shown that the phase and amplitude favourable to synchronization are prolonged just before synchronization. This agrees with Appleton's experimental results. It is also found that hysteresis occurs. The decrease in energy with the decrease in detuning is explained by the fact that the phase favourable to synchronization is that which opposes the motion and is prolonged. View full abstract»

37. The Development and Study of a Practical SpacedLoop Radio DirectionFinder for High Frequencies
Publication Year: 1947This 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»

38. The measurement of the activity of quartz oscillator crystals
Publication Year: 1946 , Page(s): 29  36Consideration is given to the various electrical quantities associated with the equivalent network of a quartz crystal which might be used to assess the Â¿activityÂ¿ that the crystal will exhibit in an oscillator circuit. It is concluded that the most generally serviceable criterion is afforded by measuring the antiresonant impedance of the parallel combination of mounted crystal and a standardized value of capacitance typical of that encountered in current oscillator designs. This is especially true for the highfrequency thicknessshearmode plates which at present constitute the bulk of the output of the industry, since these plates are practically always used in circuits in which this antiresonant impedance determines directly the amplitude of oscillation. The relations between the various possible criteria of activity are investigated. The following pieces of equipment are described:Â¿ 1. A flexible laboratory instrument capable of measuring the seriesresonant or antiresonant impedance of any crystal response in the frequency range 50 kc/sÂ¿20 Mc/s. 2. A simpler laboratory instrument capable of measuring the antiresonant impedance of any response in a restricted frequency band around selected spot frequencies. 3. An instrument designed for factory or other routine testing, in which the parallel dynamic resistance of the dominant crystal response is measured by a substitution method in an oscillator circuit. This instrument is suitable for frequencies above 3 Mc/s. 4. An instrument similar to No. 3 but slightly more complex, for the frequency range 80 kc/sÂ¿3 Mc/s. View full abstract»

39. A Table of Intermodulation Products
Publication Year: 1948 , Page(s): 31  39An expression is derived from which, by substitution of appropriate numerical values, an equation can be obtained for any of the intermodulation products which can be generated by the simultaneous transmission of any number of sinusoidal waves through a device with an output/input characteristic like V=a1v+a2v2+a3v3Â¿. This expression is used as a basis for classification of products, and a table of representative products is drawn up. Information is given about the numbers and relative importance of products of different kinds. View full abstract»

40. An Analysis of Klystron Reflector Performance
Publication Year: 1948 , Page(s): 295  301In this paper the performance of klystron reflectors is studied in detail. The electrostatic potential distribution in the reflector space is calculated by means of relaxation methods for three typical reflector designs. The transit time for electrons moving along the tube axis is calculated as a function of the h.f. voltage picked up in the resonator gap. With the help of the transittime curves the bunching is studied in detail. The advantage of this analysis as compared with the treatment by other authors is twofold: the analysis is not confined to small signals, and it is possible to attribute tube defects to features of reflector design. It is shown that the power output and the transit times as deduced from the theory are in good agreement with experimental determinations. Offaxis electron paths are then computed by means of a stepbystep method. A consideration of these paths shows that spacecharge effects are not likely to play an essential part in the performance of the tubes studied. In conclusion, the effect of the spatial focusing by the reflector on the tube impedance is discussed. View full abstract»

41. Sketch for an algebra of relay and contactor circuits
Publication Year: 1948 , Page(s): 303  312A system of symbols is described, by which the various elements (contacts and operating coils) of a relay circuit can be represented. The symbols are then linked together by signs, the resultant algebraic expression corresponding to the circuit, and the operation of the circuit can be studied by considering the behaviour of the algebraic expression according to rules which are developed in the paper. Methods are described whereby complex circuits may be simplified by algebraic manipulation of the symbolic expressions; and design of relay circuits to perform given operations is discussed. View full abstract»

42. Experiments on the electric strength of air at centimetre wavelengths
Publication Year: 1947 , Page(s): 315  324
Cited by: Papers (3)The paper is concerned with the electric strength of air when stressed by alternating fields of wavelengths 10.7 and 3.06 cm (2800 and 9800 Mc/s, respectively). The spark gaps used for the experiments consisted of either coaxialline or waveguide transmission systems, and the electric stress was applied in the form of impulses lasting for one microsecond and repeated 400 times per second. Stress determinations were made by the relationship, afforded by Poynting's vector, between stress and power conveyed along the system. The method of measurement is described. The behaviour of the spark gap is shown to be dependent on the irradiation conditions of the gap, but a minimum value of breakdown stress exists which is independent of irradiation. In all cases this minimum stress was compared at atmospheric pressure with the continuous direct breakdown stress of the gap, and was found to be approximately 70% of the direct value, irrespective of the gap length and frequency. Differences with respect to gas pressure are shown to exist between the microwave behaviour of such gaps and the corresponding directvoltage behaviour. View full abstract»

43. Fluctuations of Electric Current
Publication Year: 1946 , Page(s): 37  44Random fluctuations in the amplitude of an electric current were originally discovered in two different circumstances: (a) the fluctuation in the current through a thermionic valve, which is known as Â¿shot noise,Â¿ and (b) the voltage fluctuation at the terminals of a resistor, which is known as Â¿Johnson noise.Â¿ The theory of these two types of fluctuation is presented in outline form; and it is shown how these two aspects of the fundamentally discrete nature of the flow of electric current, when it is a stream of electrons, can be unified into a single theory of current fluctuations due to random motions of the electrons. The theory is applied also to the controversial case of a spacechargelimited thermionic valve. Subsidiary factors, such as partition of current in a screengrid valve and the behaviour of secondaryemission amplifiers, are of great technical importance, and methods of estimating the magnitude of their effects are described. The equivalent temperature of the radiation resistance of an aerial is also considered. View full abstract»

44. Tuning devices for broadcast radio receivers
Publication Year: 1946 , 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»

45. The effects of an unwanted signal mixed with the carrier supply of ring and Cowan modulators
Publication Year: 1948 , Page(s): 173  176It is shown how the performance of a ring or Cowan modulator, when the carrier supply has an unwanted signal mixed with it, can be investigated by a frequencyanalysis of its modulating function. Results obtained for particular cases lead to certain general conclusions, among which are the following:Â¿ (a) The primary modulating effect of an unwanted signal mixed with the carrier is largely independent of the resistance of the circuit supplying the carrier, even though this affects the shape of the modulating function very considerably. The amplitude of the unwanted component in the modulation is, relative to the wanted component, only about onehalf of that in the carrier input. (b) Ring and Cowan modulators give a similar performance in this respect. (c) When the frequency of the input signal is equal to the carrier frequency, the output of the difference frequency between the carrier and unwanted signal is zero for an ideal modulator, and very small for one with a carrier supply of high resistance; as the resistance is reduced, the output of difference frequency increases, until with zero resistance it has a ratio relative to a main sideband of about onequarter of the amplitude ratio of the unwanted signal relative to the carrier in the carriersupply circuit. View full abstract»

46. Reflections from Flat Sheet and Angle Reflectors
Publication Year: 1948 , Page(s): 485  488Theoretical formulae are found for the reflection from flat sheets and angle reflectors. The reflection diagram from a flat sheet is the same as the transmission polar diagram of an aperture of double the dimensions of the sheet. A small deviation from flatness considerably alters the diagram, a sag of half a wavelength at the centre producing a zero where there would otherwise have been a maximum. The rightangled corner reflector is also investigated, and the broad reflection diagram expected from geometrical optics is found. The effect of a small departure of the included angle from a right angle is also discussed. View full abstract»

47. Network Analysis by the ChainRelaxation Method
Publication Year: 1948 , Page(s): 177  182A new approach to the analysis of electrical networks, the ChainRelaxation method, is developed. Essentially the method consists: (a) in selecting a certain number of branch currents and considering them as unknowns to which arbitrary values are assigned, (b) in expressing all other branch currents, node potentials, given e.m.f.'s of voltagegenerators, and given currents of currentgenerators in terms of the selected branch currents, (c) in providing for additional Â¿residualÂ¿ external node currents in order to make the resulting voltage and current distribution physically possible, (d) in solving simultaneous linear equations for the initially selected branch currents as unknowns. A special technique is used, which is based on the superposition theorem, and which obviates the unnecessary repetition of algebraic symbols and reduces the possibility of errors. The new method leads in general to simultaneous equations with a smaller number of unknowns than the usual methods of network analysis: in many cases the number of unknowns is two only. View full abstract»

48. NonLinear Distortion in Transmission Systems
Publication Year: 1945 , 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»

49. The Use of Earth Mats to Reduce the Polarization Error of UType Adcock DirectionFinders
Publication Year: 1947 , Page(s): 91  98The paper deals with the experiments carried out in 1943?44 to investigate the use of an earth screen or mat to reduce the polarization errors of the Utype Adcock directionfinder. These errors arise from the introduction of signal voltages into the system by the horizontally polarized component of the incident waves, when the aerial feeders are laid on, or buried in, ground of poor conductivity. The polarization error of a standard form of directionfinder, erected in the normal manner on highly conductive ground (3 ? 108 e.s.u., or about 3 ? 103 ohmcm resistivity) at the Radio Research Station, Slough, was measured over the frequency range 3?10 Mc/s, with the aid of a local transmitter which radiated at controllable angles of incidence and polarization. An earth mat, about 31 m in diameter and of a square mesh between 0.3 and 1 m, was then installed at the directionfinder, and the measurements were repeated for various experimental arrangements of this installation. When the mat was raised above and insulated from the ground, the polarization error of the directionfinder was seriously increased; but when the mat was effectively earthed (both around its perimeter and at an intermediate radius) the error was slightly reduced. In place of the direct earth connection, a similar result was achieved by attaching radial wires to the perimeter of the mat, the length of the wires being selected to resonate at the frequency in use. By using a combination of 108 wires of 11, 15 and 25 m lengths, arranged so that there were 36 of each length, the desired reduction in the polarization error was attained more or less uniformly over the whole of the 3?10 Mc/s range. Additional experiments were carried out at Martlesham on ground of such poor conductivity (107 e.s.u., or about 105 ohmcm resistivity), that direct earth connection to the mat was ineffective. The results confirmed the previous deduction that the attachment of radial wires of suitable length and disposition make s the earth mat effective. It was also shown that both mat and radial extension wires may be laid on the ground if desired. Furthermore, it was shown that, with the mat in position, it was no longer necessary to bury the aerial feeders, but was sufficient to lay the feeders on the ground just under the mat, or along the surface of the mat, if the feeder screen was well bonded to the mat. An additional advantage of the use of such an arrangement is that it smooths out the effects of any irregularities in the ground at the site, and produces a corresponding improvement in the performance of the directionfinder. Comparison of observations made at the same site with two directionfinders, one equipped with an earth mat and one without, showed that when taking bearings on signals from stations at distances ranging from 200 km to nearly 800 km, the expected appreciable improvement in overall performance due to the mat was attained. View full abstract»

50. The Estimation and Forecasting of ShortWave Propagation Conditions, with special reference to Naval Communications
Publication Year: 1948 , Page(s): 351  362The paper describes the development and application of techniques for the use of ionospheric data in the solution of highfrequency communication problems, during the years 1941Â¿1945, at the Admiralty Signal Establishment. An account is given of the investigation of the computation of ionospheric absorption, and of the technique developed for the determination of lowest usable high frequency based on this investigation. Semiempirical expressions are derived for ionospheric absorption for both short and longdistance transmission. The formulae were found to fit well with existing ionospheric absorption data. A brief summary is also given of the general underlying principles of shiptoshore communication. Using ionospheric methods, charts were developed to enable ships to choose the optimum frequency of transmission or reception with a given base. Charts were constructed for special services, and also for general use, embracing the whole network of naval shore receivingstations. 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.