Showing papers in "Journal of the Institution of Electrical Engineers in 1949"
TL;DR: In this paper, the problem of ground-wave propagation over an inhomogeneous smooth earth is discussed in terms of the known solution for a homogeneous earth, and the fundamental results of the theory for homogeneous Earth are described in a form directly useful to the argument.
Abstract: The problem of ground-wave propagation over an inhomogeneous smooth earth is discussed in terms of the known solution for a homogeneous earth. The inhomogeneity refers only to changes in the earth constants from place to place, and the problem is idealized by assuming a wave radiated from a vertical dipole over a series of homogeneous annular sections. After a statement of some of the conditions the solution would be expected to obey, including the essential one of reciprocity, some fundamental results of the theory for a homogeneous earth are described in a form directly useful to the argument. The solution is first given for the short-wave limit, where it is complete except in the neighbourhood of a boundary. By an approximate consideration of the energy flow at different heights above the ground, the solution is extended to the case of intermediate wavelengths where the first and last boundaries are in the diffraction region of the transmitting and receiving points respectively. It is then shown that a well-known empirical method yields the same solution when it is made reciprocal by taking the geometric mean of the value it gives and the value that would be obtained with the transmitter and receiver interchanged. This method is formally used to obtain a tentative solution for the effect of the disturbance function in the neighbourhood of a boundary. It leads to the striking suggestion that on passing from a section of one value of conductivity to another of a higher one, there is a recovery in field-strength before the attenuation of the wave becomes characteristic of the new section. On crossing the boundary in the other direction, there is a correspondingly increased drop in field strength before the attenuation takes its new characteristic type. Owing to the lack of sufficiently controlled conditions, most of the existing experimental results are inconclusive with regard to these features at a boundary, but some evidence is given in support of them. Stress is laid on the need for further experiments specifically designed to study the field near a land-sea boundary. The paper deals briefly with the practical application of the method, and gives a specimen field-strength/distance curve for a route consisting of several land and sea sections. It concludes by pointing out that further research is needed, especially with regard to the phase relationships, as the argument has dealt only with field-strength values.
135 citations
TL;DR: A lumped-constant equivalent of a transmission line can be obtained in general in the form of a symmetrical lattice, in which the series and lattice arms are inverse and approximate respectively to the shortcircuit and open-circuit impedances of half the line as discussed by the authors.
Abstract: A lumped-constant equivalent of a transmission line can be obtained in general in the form of a symmetrical lattice, in which the series and lattice arms are inverse and approximate respectively to the short-circuit and open-circuit impedances of half the line. One such set of approximations can be derived from the infinite ladder networks (Cauer's canonical form) equivalent to these impedances. These approximations produce all-pass constant-impedance networks (dissipation being neglected) in which the delay is maximally flat in the sense that the first 2m ? 1 derivatives of the delay with respect to frequency are zero at the origin; m is an integer expressing the order of the approximation.
95 citations
TL;DR: In this paper, a radio method for the measurement of winds in the ionosphere is described, where a pulse transmitter working on about 4 Mc/s is used in conjunction with three receivers placed at the corners of a right-angled triangle, and separated by distances of the order of 100 m. The results of 82 determinations of winds by the use of local pulse transmitters are presented in Figs. 7, 8 and 9 in the form of histograms.
Abstract: A radio method for the measurement of winds in the ionosphere is described. A pulse transmitter working on about 4 Mc/s is used in conjunction with three receivers placed at the corners of a right-angled triangle, and separated by distances of the order of 100 m. A simultaneous record is made of the fading of a single radio pulse reflected from the ionosphere and received at the three receivers. If a steady wind is blowing in a non-turbulent ionosphere the three fading records are displaced in time and the velocity and direction of the wind can be deduced. Many of the records obtained are sufficiently simple for reliable deductions to be made.The results of 82 determinations of winds by the use of local pulse transmitters are presented in Figs. 7, 8 and 9 in the form of histograms. The most frequent velocity is found to be of the order of 50 m/sec in a direction towards north-west, but there are clear indications that this velocity varies throughout the day, probably with a semi-diurnal period. The results are compared with previous measurements made by other methods.Measurements have also been made in which a distant pulsed transmitter has been used in conjunction with the same arrangement of receiving aerials. In all the experiments care was taken to avoid the misleading conclusions which may be drawn when “polarization fading” occurs owing to the simultaneous presence of two magnetoionic components in the reflected pulse.
86 citations
TL;DR: In this paper, the properties required of a storage system, and its operation as part of a machine, are stated, and an instruction would be set up and obeyed in 600 μsec.
Abstract: The requirement for digital computing machines of large storage capacity has led to the development of a storage system in which the digits are represented by a charge pattern on the screen of a cathode-ray tube. Initial tests have been confined to commercial tubes. Shortterm memory of the order of 0.2 sec is provided by the insulating properties of the screen material. Long-term memory is obtained by regenerating the charge pattern at a frequency greater than 5 c/s. The regeneration makes accurate stabilization of the position of the charge pattern on the c.r. tube unnecessary. The properties required of a storage system, and its operation as part of a machine, are stated. If such a machine were operated in the series mode, an instruction would be set up and obeyed in 600 μsec.
68 citations
TL;DR: In this paper, a simple form of electrolytic tank and its application to this and allied measurements, including that of transient response, is described, and an overall accuracy to within 1% has been obtained by the elimination of the tank boundary errors and of electrode polarization troubles.
Abstract: An analogy relating the impedance functions of linear networks of lumped elements to the potential distribution and current flow in a uniform sheet of conducting material, set up by point electrodes, has been described by Daniell. Electrolytic tank computors, based on this analogy, have been used hitherto purely for the measurement of the steady-state response characteristics of such networks, from a knowledge of the poles and zeroes of their steady-state impedance functions. A simple form of electrolytic tank and its application to this and allied measurements, including that of transient response, are described. An overall accuracy to within 1% has been obtained by the elimination of the tank boundary errors and of electrode polarization troubles. The application of the electrolytic tank has been extended to the practical determination of the residues at the poles of the impedance function, and a known practical method is referred to, whereby the zeroes of the polynomials forming the impedance function may be determined by measurement. A rapid automatic means of measuring the steady-state characteristics corresponding to a given pole and zero distribution is described.
39 citations
TL;DR: In this article, the intrinsic electric strength of polythene, polystyrene, polyisobutene, polymethyl methacrylate, chlorinated polythenea and oxidized polythenes have been measured over the temperature range -200° to + 110°C.
Abstract: The intrinsic electric strengths of polythene, polystyrene, polyisobutene, polymethyl methacrylate, chlorinated polythene and oxidized polythene have been measured over the temperature range -200° to + 110°C. At low temperatures the electric strengths of the non-polar polymers, polythene, polystyrene, and polyisobutene, do not vary much with temperature; for each of them there is a characteristic temperature above which the electric strength falls rapidly with further temperature rise. This temperature is about 40° C for polythene, 90° C for polystyrene, and -50° C for polyisobutene. The electric strength of the polar polymer, polymethyl methacrylate, is much higher than those of the non-polar polymers at low temperatures, and falls with increasing temperature throughout the temperature range investigated; there is an increased rate of change of electric strength with temperature above 20° C. Mild chlorination of polythene leads to an increase in the electric strength at low temperatures, a decrease at high temperatures, and a lowering of the temperature at which the temperature gradient changes. At low temperatures the electric strength of oxidized polythene is greater than the corresponding strength of unoxidized polythene. The results are discussed in the light of Froohlich's electronic theory of breakdown.
30 citations
TL;DR: In this paper, a review of some theories suggested to explain the production of fading in terms of an ionosphere with varying irregularities in the horizontal plane is given, and the theoretical nature of the fading curve, both with regard to the distribution of amplitude and the variation with time, is indicated.
Abstract: The fading of radio waves of medium and high frequencies returned from the ionosphere is analysed. The experimental data on high frequencies were recorded by the author at normal incidence using a pulse transmitter, and, when necessary, a circularly polarized receiving aerial. The medium-frequency records were made by the B.B.C. using continuous-wave transmissions from broadcasting stations at different distances up to 1 500 kilometres.A review is given of some theories suggested to explain the production of fading in terms of an ionosphere with varying irregularities in the horizontal plane. The theoretical nature of the fading curve, both with regard to the distribution of amplitude and the variation with time, is indicated, and is compared with experimental results.It is shown that all fading curves can be explained in terms of a wave which is the sum of a steady, specularly reflected component, and a random component with a Rayleigh distribution of amplitude. The relative magnitudes of these two components have been determined for a series of different conditions, and the results are summarized. It is also shown that the rate of variation of the amplitude of the received signal is approximately, but not exactly, in accord with the theories, and from this rate of change it is possible to calculate the “effective velocity” of the irregularities in the ionosphere. If the fading is caused by irregular “turbulent” motions of the irregularities, the “effective velocity” is the r.m.s. velocity of these motions; if it is due to a steady drift of the irregular ionosphere as a whole with a velocity vw, then the “effective velocity” is approximately equal to vw/14. The “effective velocities” deduced from 122 records made at vertical incidence, and 55 made at oblique incidence, lie between 0.3 and 8.0 m/sec and have an average value of 1.9 m/sec.
28 citations
TL;DR: In this article, an account of work carried out at the Telecommunications Research Establishment on the design and use of Yagi aerial arrays during the period 1938-42 is given, where the types of polar diagrams obtained when the design parameters are changed are deduced from vector diagrams.
Abstract: An account is given of work carried out at the Telecommunications Research Establishment on the design and use of Yagi aerial arrays during the period 1938-42. An attempt is made to give sufficient information in tabular form for an aerial of given characteristics to be designed approximately. Final adjustment by experiment will be required unless a previous design is copied exactly. The advantages and limitations of multiple Yagi arrays are considered and a simple theoretical explanation of the mode of operation of a Yagi aerial is given. The types of polar diagram obtained when the design parameters are changed are deduced from vector diagrams. Only aerials of length greater than one wavelength are considered. These normally consist of three or more directors in addition to an exciter and a reflector.
25 citations
TL;DR: In this article, the breakdown strength of air has been determined for alternating electric fields of frequencies between 100 and 300 Mc/s for parallel plane gaps up to 1 mm wide, and it has been shown that breakdown may be initiated in one of three different ways, each of which may be represented by a curve that separately obeys Paschen's law.
Abstract: The breakdown strength of air has been determined for alternating electric fields of frequencies between 100 and 300 Mc/s. Parallel plane gaps up to 1 mm wide have been investigated. A description is given of the apparatus employed, together with details of a dielectric voltmeter which has enabled the voltage across the breakdown gap to be measured accurately. A discontinuity is shown to exist in the relation between the breakdown stress and the gap width. The breakdown stress for small gap widths appears to follow a curve representing values some 10-15% below those obtained with direct current. At a critical gap width, which is dependent primarily on the frequency of the applied electric field, there is a sudden decrease in the electric stress at which breakdown occurs, to a constant value, which for atmospheric pressure is 29 kV/cm. The critical gap width is found to vary slightly with gas pressure, and may be increased by the application of a small d.c. electric field across the gap. An examination of the results shows that under transition conditions Paschen's law is not applicable. A theory is put forward on the basis that breakdown may be initiated in one of three different ways, each of which may be represented by a curve that separately obeys Paschen's law.
20 citations
TL;DR: In this paper, the results of room-temperature measurements on ceramic (polycrystalline) specimens of magnesium, calcium, strontium and barium titanates at frequencies of 1.5 and 9450 Mc/s (3.18 cm) were given.
Abstract: The paper gives the results of room-temperature measurements on ceramic (polycrystalline) specimens of magnesium, calcium, strontium and barium titanates at frequencies of 1.5 and 9450 Mc/s (3.18 cm), and on barium titanate at 24000 Mc/s (1.25 cm). It is found that the latter material is unique among this series in showing a considerable fall in permittivity, and a large increase in the loss tangent, at the higher frequencies, compared with the behaviour at 1.5 Mc/s. Variable temperature measurements on barium titanate show that the crystallo-graphic change which is known to occur around 120°C, the Curie point of the material, affects the permittivity at 9450 and 1.5 Mc/s in an analogous manner. Room-temperature measurements at the same frequencies on a range of barium-strontium titanate compositions are also described, and attention is drawn to the composition 56% BaTiO3: 44% SrTiO3, having a permittivity of 760 and loss tangent of 0.02 at 9450 Mc/s and 20°C, as likely to be of value in microwave work. The difficulties associated with the measurement of high-permittivity values at centimetre wavelengths are discussed, and a full description is given of the three methods developed for different parts of the investigation.
17 citations
TL;DR: In this article, the authors considered the rise of the total flux as retarded by eddy currents and showed that for this purpose all eddy-current paths can be represented by a single fictitious damping-ring whose resistance and leakage reactance are calculated from first principles.
Abstract: In designing machines and apparatus with solid or partly solid magnetic circuits, such as eddy-current brakes, clutches, impact exciters, and rolling-mill motors, flux/time curves have often to be predetermined to secure a desired rapidity of response. The prediction has hitherto been uncertain, especially in the absence of test results on similar machines, and expensive changes of design, introducing laminated poles and yokes have sometimes been resorted to where the standard design or a simple modification of solid sections would have sufficed. The paper considers the rise of the total flux as retarded by eddy currents and shows that for this purpose all eddy-current paths can be represented by a single fictitious damping-ring whose resistance and leakage reactance are calculated from first principles. Simple expressions for the usual shapes of iron section are developed, and the test results which are given provide agreement between theory and experiment. For magnetic circuits which consist of solid iron in parts only and with fairly large air-gaps as in d.c. machines and alternators, it will generally suffice to take account only of the resistance of the fictitious damping-ring and to ignore its leakage reactance. A graphical procedure may then be used for obtaining the flux/time curve very rapidly. The error thus introduced makes the response appear rather less rapid than it is in reality. Where greater accuracy is needed, the leakage reactance of the substitute damping-ring has to be introduced and the solution found by solving transformer equations for successive parts of the characteristic. The substitute damping-ring, as a theoretical device, should prove helpful in solving other problems involving eddy currents by converting the system into a transformer with short-circuited secondary.
TL;DR: In this article, the capacitance changes in air capacitors due to moisture in the atmosphere were investigated and it was shown that these changes may be considerably in excess of those due to the alterations in the permittivity of the air.
Abstract: The paper describes measurements, at a frequency of 1 000 c/s, of the capacitance changes in air capacitors due to moisture in the atmosphere. It is shown that these changes may be considerably in excess of those due to the alterations in the permittivity of the air. Over the range of relative humidity 30–65% the total change in capacitance can be about 3 parts in 10 000 at room temperatures. The full advantage of the otherwise high stability of a precision air capacitor is lost when this effect is ignored.
TL;DR: In this article, the modes existing in a circular waveguide with walls of finite conductivity are investigated and expressions derived for the corrections to the attenuation constant of a piston attenuator.
Abstract: The modes existing in a circular waveguide with walls of finite conductivity are investigated and expressions derived for the corrections to the attenuation constant of a piston attenuator. The correction is negligible for E-modes but may be of importance in work of the highest accuracy when H-modes are used. Similar corrections are derived for the effect of an oxide layer on the inner surface of the attenuator.
TL;DR: In this article, the pioneer theory of Bailey and Martyn is restated in a form which relates it more closely to standard ionosphere theory, and the experimental results are summarized in the form which enables the magnitude of the cross-modulation effect to be deduced approximately for any pair of stations.
Abstract: Existing theoretical and experimental knowledge is surveyed. The pioneer theory of Bailey and Martyn is restated in a form which relates it more closely to standard ionosphere theory. The experimental results are summarized in a form which enables the magnitude of the cross-modulation effect to be deduced approximately for any pair of stations. The way in which observations of cross-modulation can be used in ionospheric research is outlined.
TL;DR: In this paper, a simple method of modulator analysis is given which enables the performance of a modulator with frequency-selective terminations to be determined so long as these terminations are resistive, zero or infinite at all significant frequencies.
Abstract: A simple method of modulator analysis is given which enables the performance of a modulator with frequency-selective terminations to be determined so long as these terminations are resistive, zero or infinite at all significant frequencies. Most of the cases likely to be useful or unavoidable in practice have been worked out for the ring, Cowan (shunt-type) and series modulators, and the optimum terminating resistances (assumed equal) and minimum insertion losses have been tabulated in terms of the rectifier ratio and geometric mean resistance.
TL;DR: In this paper, the authors summarized theoretical and practical investigations into the cause and properties of site errors at metre wavelengths, mainly directed to Adcock-type aerial systems; but other classes of instrument are considered in an Appendix.
Abstract: The paper summarizes theoretical and practical investigations into the cause and properties of site errors at metre wavelengths. Attention is mainly directed to Adcock-type aerial systems; but other classes of instrument are considered in an Appendix. A criterion is there suggested to express the susceptibility of a direction-finder to site error, and is applied to well-known instrumental types. With some simplifying assumptions, the variations in error with azimuth and elevation angle due to ?point?, ?linear? and ?sheet? type reflecting obstacles are examined. Certain properties of error charts which may be useful in locating the sources of error on a site are discussed. Errors introduced by randomly dispersed obstacles are considered from a statistical viewpoint. The theoretical and practical difficulties encountered in calibrating a site are discussed, the limitations of correction processes involving the use of previously measured error data being pointed out. Practical techniques available for locating the effective reflecting obstacles on a site are described, and examples of their application are given. Methods for suppressing unwanted reflections are considered. The work has led to a better understanding of site error phenomena at metre wavelengths, but further experimental work, linked with theoretical studies, is necessary.
TL;DR: In this paper, the performance of a capacitor transformer with compensating reactor and intermediate voltage transformer is analyzed and design formulae are developed which should serve to provide sufficient data for a comparison to be made with the usual electromagnetic type.
Abstract: It is well known that voltage transformers of the usual electromagnetic type constitute a very costly item in high-voltage systems. Considerable savings could be effected by the use of voltage transformers of the capacitor type if their design could be perfected to give sufficient accuracy, i.e. if their ratio errors and phase angles under varying operating conditions could be reduced to values within such limits as are laid down in various standard specifications. The performance of a capacitor transformer with compensating reactor and intermediate voltage transformer is analysed in this paper and design formulae are developed which should serve to provide sufficient data for a comparison to be made with the usual electromagnetic type. It is suggested that savings are likely to be effected by the use of the capacitor voltage transformer in systems of 66 kV and above.
TL;DR: In this article, the steady state and transient operation of an amplifier having one of the two basic circuits analysed, depend on only three dimensionless coefficients, and a simple semi-graphical method of determining the steady-state current and flux waveforms, and the response to sudden changes in input, has been obtained.
Abstract: The mathematical analysis of magnetic amplifiers is made difficult by the non-linear characteristic of the iron. By simplifying the problem (neglecting leakage reactance and assuming an ideal B/H characteristic) a solution can be obtained which shows that the steady-state and transient operation of an amplifier having one of the two basic circuits analysed, depend on only three dimensionless coefficients. This solution leads to simple semi-graphical methods of determining the steady-state current and flux waveforms, and the response to sudden changes in input; satisfactory agreement between experimental results and theory has been obtained. Improvements in core characteristics have led to a simplified method of designing amplifier windings, and by special circuits amplifier delays have been reduced in the ratio of about 10:1.
TL;DR: In this paper, a continuation of investigations described in an earlier paper has been carried out on quenched and unquenched polythene, the former possessing a structure which differs markedly from that of the previous specimens, but no significant difference is found.
Abstract: This note describes a continuation of investigations described in an earlier paper1 Specimens of the type formerly tested contained partly oriented crystalline spherulites of considerable size (up to 510−3 cm diameter), and it was considered advisable to investigate whether this type of structure affected the electric strength Further measurements have accordingly been made on quenched and unquenched polythene, the former possessing a structure which differs markedly from that of the previous specimens, but no significant difference is found
TL;DR: Blumlein this paper proposed a mutual-admittance bridge with inductively coupled ratio arms, which enables the direct impedance between two points to be measured independently, within limits, of any impedances connected between a third point and the two terminals of the impedance being measured.
Abstract: Part 1 of the paper is concerned with the theory of a.c. bridges in which the ratio arms consist of tightly-coupled inductors, and refers particularly to bridges in which two sets of such ratio arms are used together in order to obtain very large ratios between the unknown and standard impedances. Reference is made to the important property of inductively-coupled ratio arms which enables the direct impedance between two points to be measured independently, within limits, of any impedances connected between a third point and the two terminals of the impedance being measured. The logical development of bridges with two such ratio arms follows. The material in Part 1 of the paper is the original work of the late A.D. Blumlein, B.Sc.(Eng.), Associate Member, and the present authors have used verbatim a considerable portion of a hitherto unpublished memorandum written by him in January, 1941. Part 2 of the paper describes Blumlein's application of the principles described to a general-purpose mutual-admittance bridge for the measurement of capacitance and resistance. This has a wide range of impedance measurement, and the facility of being able, in many circumstances, to measure components in situ when it is difficult or impossible to isolate them from other components of a circuit.
TL;DR: In this article, a general theorem concerning the influence of the Thomson effect on the location of the maximum temperature in an electrical contact is given, and its application to the theory of fine transfer in electrical contacts is discussed.
Abstract: A general theorem is given concerning the influence of the Thomson effect on the location of the maximum temperature in an electrical contact. Its application to the theory of fine transfer in electrical contacts is discussed.
TL;DR: In this paper, the magnitude and distribution of harmonic currents flowing in a c.c. networks were investigated from a theoretical aspect, using equivalent networks, experimental verification of these theories being given for certain simple cases.
Abstract: The paper deals with the magnitude and distribution of harmonic currents flowing in a.c. networks. The various sources of harmonics are discussed in general, and harmonics arising from the use of mercury-arc rectifiers and in h.v. transmission are dealt with in greater detail. The flow of harmonics arising from these sources is considered from a theoretical aspect, using equivalent networks, experimental verification of these theories being given for certain simple cases. The possibility of a complete theoretical solution is shown, and certain probable practical conclusions are drawn. Various methods of reducing harmonics are discussed, and the relative importance of the various sources is considered in the light of modern trends in harmonic suppression.
TL;DR: In this paper, the fading of a single magneto-ionic component of a radio wave of frequency 2-6 Mc/s reflected from the ionosphere at vertical incidence has been recorded at two receiving points separated by about 100 m.
Abstract: The fading of a single magneto-ionic component of a radio wave of frequency 2–6 Mc/s reflected from the ionosphere at vertical incidence has been recorded at two receiving points separated by about 100 m. On several occasions it has been deduced from the records that the fading is not due to the regular drift of a constant ground-distribution of e.m.f. past the observing point, but that it corresponds to a ground distribution which is varying irregularly at all points. Records obtained under these circumstances have been analysed on the assumption that the fading is caused by the random movement of irregularities in the ionosphere according to the theory suggested by Ratcliffe.9The results agree, to a first order, with the assumption that in the ionspheric reflecting region there are irregularities moving with velocities in the line of sight which are distributed in a Gaussian manner with r.m.s. value of approximately 2 to 3 m/sec. There is, however, a significant discrepancy between the records and the results of the simple theory, and possible ionospheric causes for this discrepancy are discussed.There is some experimental evidence to suggest that the irregularities responsible for the fading are situated below the point where waves of frequency 4 Mc/s are reflected from region E.
TL;DR: In this article, it was shown that slot ripples in the open-circuit e.m.f. waveform of salient-pole synchronous machines are caused by the interaction of rotor permeance harmonics with those set up by the stator slot-openings.
Abstract: A review of the literature of the subject shows the wide acceptance of the view that slot ripples in the open-circuit e.m.f. waveform of salient-pole synchronous machines are caused by the interaction of rotor permeance harmonics with those set up by the stator slot-openings. It is shown in the paper that this is usually only a secondary cause and that these ripples are due primarily to stator slot-frequency currents flowing in secondary circuits on the rotor; as a consequence the ripples may be generated with either a smooth or salient-pole rotor. It is further shown that e.m.f. ripples may be generated not only when the stator slots per pole-pair are even but also when they are odd or fractional. These e.m.f. ripples may correspond to the fundamental or a higher harmonic of the flux-density variation due to the stator slot-opening. Expressions are derived for the frequencies of the ripples in the special cases, such as turbo-alternators and synchronous motors with smooth-slotted rotors, where the squirrel-cage winding is placed in uniformly-indexed slots. Various methods for reducing or suppressing these ripples are discussed and corresponding formulae derived. The paper concludes with a detailed examination of a number of oscillograms and the appropriate data of the machines to which they refer.
TL;DR: In this article, a height indicator for aircraft is described in which a change in capacitance with altitude is measured at an audio frequency, indicated on a meter, which is calibrated in feet.
Abstract: A height indicator for aircraft is described in which a change in capacitance with altitude is measured at an audio frequency. The capacitance change is indicated on a meter, which is calibrated in feet. Two insulated metal electrodes are mounted on the aircraft, and the direct capacitance between them is measured. This capacitance is affected by the earth, which behaves as a conducting sheet, and the variations can be used to determine the altitude of the aircraft. The changes in capacitance are minute, and measurement is made difficult by the presence in the system of other and much larger capacitances. The difficulties can be overcome by using the double-ratio a.c. bridge described in the associated paper, and the sensitivity can be made sufficient to enable capacitance changes of 1 μμμF to be detected. AS the altitude of the aircraft increases, the capacitance changes caused by the earth become ever smaller, and are eventually obscured by changes arising from other causes. The method is, therefore, suitable only for measuring low altitudes; but, within its range, it is capable of some accuracy.
TL;DR: In this paper, an experimental determination of the usefulness and limitations of elementary theory in estimating the fields scattered by metal wires and sheets, treated as passive scattering-elements, is made.
Abstract: The paper describes an experimental determination of the usefulness and limitations of elementary theory in estimating the fields scattered by metal wires and sheets, treated as passive scattering-elements. The results are of interest in assessing errors due to obstacles on a direction-finding site. Formulae are derived for the scattered fields, using the transmission-line theory for wires and diffraction theory for sheets. A method is described for the measurement of scattered fields and the results of measurements on various wires and sheets, at a frequency of 600 Mc/s (50 cm), are shown to be in substantial agreement with the elementary theory. The measured amplitudes of the resonance peaks which occur in the field scattered by a wire as the length of the wire is varied are, however, much smaller than would be expected, except for wires less than two wavelengths long. The results indicate that for wires of the order of 1-mm diameter resonance effects at a frequency of 600 Mc/s are small if the length of the wire is more than about five wavelengths. This conclusion is probably true for a wide range of wire diameters and frequencies. Resonance effects in sheets may be neglected if the dimension of the sheet normal to the electric vector is greater than a wavelength. It is concluded that scattered fields may be computed from elementary theory to the accuracy normally required in direction-finding work.
TL;DR: In this paper, the principal causes of error in the rubber model are discussed and, in some simple cases, evaluated, and it is shown that errors due to the configuration of the membrane and ball spin can be reduced without limit by decreasing the scale of deformation of the rubber membrane.
Abstract: The principal causes of error in the rubber model are discussed and, in some simple cases, evaluated. It is shown that errors due to the configuration of the membrane and ball spin can be reduced without limit by decreasing the scale of deformation of the membrane. Energy loss due to friction is the limiting factor, and a method is described by which this may be measured (as a function of ball speed), results being given for balls of various sizes rolling over a pure rubber surface.In general, a reduction in the area of the membrane and an increase in the ball diameter are advantageous, subject to constructional limitations. For a path length of about one foot and a ball diameter of one inch, errors in ball energy can be maintained below 2%.
TL;DR: It has been found that frequency fluctuations vary in magnitude in a random manner, and the second part of the paper indicates how useful information may be extracted from the highly complex data that result from continuous measurement.
Abstract: The first part of the paper discusses the occurrence of unwanted Actuations of frequency in sound recording and reproducing systems and considers methods of measuring these fluctuations in disc-recording systems. A particular procedure is discussed in detail and new apparatus that has been developed for these measurements is described. It has been found that frequency fluctuations vary in magnitude in a random manner, and the second part of the paper indicates how useful information may be extracted from the highly complex data that result from continuous measurement. The statistical properties of the variations of magnitude have been found to be in accordance with theory developed for analogous electrical systems, and examples are given of a number of practical cases in which statistical analysis has enabled the causes of frequency fluctuations to be identified and appropriate action to be taken.
TL;DR: In this article, it was shown that the discrepancy is at least partly caused by a variation of the effective permeability and resistivity across the lamination thickness, and that the reduction of effective permutation, due to the inability of the elementary irreversible changes of magnetization (Barkhausen jumps) to be completed in the time available, could also contribute to a discrepancy loss.
Abstract: It is normal to regard the loss in a ferromagnetic material undergoing magnetization as the sum of a hysteresis loss, which might be measured by a ballistic method, and an eddy-current loss, calculable from a knowledge of the shape and resistivity of the material and the flux changes involved. For some sheet steels the measured loss is considerably in excess of this sum, and it is with this discrepancy that the paper is concerned. A pulse method of excitation is used, a constant voltage being applied suddenly to the specimen for times ranging from 0.2 to 2.5 microsec. It has been found that, in most instances, B/H curves are either linear or can be closely approximated by functions of the form B = B(1−e−αH) or B = B(e−αH−1), where B and α are constants. By adopting these exponential expressions, accurate calculation of eddy-current losses in the non-linear regions has been made possible. In the paper, several theories of the cause of the discrepancy are suggested and examined in the light of experimental evidence in which the rate of change of mean flux density, the polarizing field, the grain orientation and the lamination thickness are varied. It is concluded that the discrepancy is at least partly caused by a variation of permeability and resistivity across the lamination thickness; but it is also shown that a reduction of the effective permeability, due to the inability of the elementary irreversible changes of magnetization (Barkhausen jumps) to be completed in the time available, could also contribute to a “discrepancy loss” which would vary with the factors above in a manner consistent with the experimental results.
TL;DR: A summary of the available knowledge of surge phenomena and for convenience of treatment this is divided into five parts; lightning and lightning surges, surge propagation, distribution of surge voltages in inductive apparatus, effects of surges on insulation and surge protective devices as discussed by the authors.
Abstract: Sections 2-6 give a summary of the available knowledge of surge phenomena and for convenience of treatment this is divided into five parts; lightning and lightning surges, surge propagation, distribution of surge voltages in inductive apparatus, effects of surges on insulation and surge protective devices. The first part of this indicates the importance of lightning-current measurements and specifies the various types of lightning surge which can occur on overhead lines. The second part draws attention to those aspects of surge propagation which are important in relation to the protection of substation apparatus, with special emphasis on the protection afforded by attenuation by corona. The third part discusses the problem of designing transformers to withstand surges and refers to the question of surge testing. The fourth part gives a summary of the available data on the surge strength of relief gaps, line insulators and cables. The fifth part summarizes the characteristics of recognized protective devices. The summary of available knowledge is followed by specific recommendations for its application to the protection of various types of overhead transmission line and of substation. Finally, attention is drawn to the need for further research, and suggestions for new researches or extensions of existing researches are made.