Showing papers in "Bell System Technical Journal in 1936"
TL;DR: The use of increasingly higher power levels in broadcasting in the last few years has attached new importance to the matter of more efficient operation of the high-power stages in radio transmitters and the resulting reductions in cost of power, size of high-voltage transformers and rectifier, and water cooling requirements, are of particular importance in transmitters having outputs of 50 kilowatts or more as discussed by the authors.
Abstract: HE use of increasingly higher power levels in broadcasting in the last few years has attached new importance to the matter of more efficient operation of the high-power stages in radio transmitters. The resulting reductions in cost of power, size of high-voltage transformers and rectifier, and water cooling requirements, are of particular importance in transmitters having outputs of 50 kilowatts or more.
700 citations
TL;DR: In this article, a review of the general aspects of the classical electromagnetic theory several equivalence theorems are established and illustrated with a number of examples from the diffraction theory.
Abstract: After a review of the general aspects of the classical electromagnetic theory several “equivalence” theorems are established and illustrated with a number of examples from the diffraction theory. Then follows a discussion of possible applications of these theorems to radiation problems. The latter part of the paper is devoted to the calculation of the power radiated from an open end of a coaxial pair.
260 citations
TL;DR: In this article, the authors deal with the mathematical theory of wave transmission in two novel kinds of cylindrical wave guides of circular cross section; namely, the hollow conductor and the dielectric wire.
Abstract: Following a brief historical sketch, this paper deals with the mathematical theory of wave transmission in two novel kinds of cylindrical wave guides of circular cross section; namely, the hollow conductor and the dielectric wire. These transmission systems behave as high pass filters with exceedingly high critical frequencies. The attenuation and impedance characteristics of the hollow conductor, heretofore ignored as far as the writers are aware, are given especial attention. This investigation discloses the remarkable fact that there exists in this system one and only one type of wave, the attenuation of which decreases with increasing frequency, a characteristic which attaches to no other type of guided wave known to the writers.
115 citations
TL;DR: In this article, the authors describe a form of electrical propagation where electromagnetic waves are sent through guides made up either of an insulator alone or of an air insulator surrounded by a conductor.
Abstract: A peculiar form of electrical propagation is described below. It makes use of extremely high frequencies — even beyond those generally employed in radio. In some respects it resembles ordinary wire transmission but unlike the latter there are no return conductors, at least of the usual kind. In this transmission, electromagnetic waves are sent through guides made up either of an insulator alone or of an insulator surrounded by a conductor. In a special case this insulator may be air. There are at least four different types of waves or electrical configurations that may be propagated. One of them is such that theory indicates its attenuation through a hollow conductor continuously decreases with increase of frequency. Although the paper deals largely with the nature of this transmission, some of the fundamental pieces of apparatus used in experimental work are described. They include generators, receivers and wave-meters.
97 citations
TL;DR: In this paper, the spontaneous voltage fluctuations and the signal due to acoustic modulation are affected in almost an equivalent manner by the applied d.-c. voltage across the resistance R, α and β are constants having values of about 1.85 and 1.25, respectively, and F 2 and F 1 are the limits of the frequency range over which the fluctuation voltage is measured.
Abstract: Voltage fluctuations which occur in resistance elements of the granular type when a direct current is flowing have been measured in the granular carbon microphone, commercial grid leaks, and sputtered or evaporated metal films. The results can be experessed by the formula $\overline{V_c^2} = KV^\alpha R^\beta \log (F_2/F_1),$ where $\overline{V_c^2}$ is the mean square fluctuation voltage, V is the d.-c. voltage across the resistance R, α and β are constants having values of about 1.85 and 1.25, respectively, and F 2 and F 1 are the limits of the frequency range over which the fluctuation voltage is measured. The constant K depends, among other things on the temperature, the surrounding medium, and the dimensions and material of the resistance element; for a commonly used carbon transmitter at ordinary operating conditions its value is about 1.3 × 10−11. The spontaneous voltage fluctuations and the signal due to acoustic modulation are affected in almost an equivalent manner by the applied d.-c. voltage which suggests that the two effects arise from the same type of mechanism, namely a fluctuating resistance at the points of contact between granules. Experiment shows that although the acoustic signal produces a resistance modulation which is in phase at all contacts the spontaneous resistance fluctuations are completely random. On the assumption that a region of secondary conduction, wherein the resistance fluctuation lies, surrounds each area of primary conduction as postulated in recent contact theory a value of β consistent with experiment has been deduced. On the further assumptions that thermal energy produces the mechanical fluctuations and that the equipartition law governs the distribution of energy between oscillators the observed frequency distribution follows.
47 citations
TL;DR: In this article, the basic relations between the magnetic characteristics of the core of a coil and the inductance and resistance of the coil as measured on an alternating current bridge are discussed.
Abstract: A resume is given of the basic relations between the magnetic characteristics of the core of a coil and the inductance and resistance of the coil as measured on an alternating current bridge. Modifications of the simple relations to take account of the interactions of eddy currents and hysteresis in the core material are developed, and are seen to require a more complicated interpretation of the data in order to obtain an accurate separation of the eddy current, hysteresis, and “residual” losses. Means are described of minimizing or eliminating the disturbing effects of distributed capacitance, leakance and eddy current loss in the coil windings. Essential details of the alternating current bridge and associated apparatus, and of the core structure, are given.
40 citations
TL;DR: In this paper, a theoretical study of the properties of a condenser, one plate of which is free to vibrate, when it is included in a circuit containing a generator, the frequency of which was higher than the resonant frequency of the plate and unrelated thereto, was presented.
Abstract: A theoretical study is presented of the properties of a condenser, one plate of which is free to vibrate, when it is included in a circuit containing a generator, the frequency of which is higher than the resonant frequency of the plate and unrelated thereto. It is shown that the plate may be maintained in oscillation at a frequency at or near its mechanical resonance, at the expense of the energy supplied by the generator, provided certain conditions are satisfied. The most favorable condition is one in which the plate is resonant at the frequency of its vibration and the electric circuit is resonant at that of the generator, and at the difference between the generator and plate frequencies, and is anti-resonant at their sum. Under these conditions the generator voltage must exceed a threshold value determined by the impedances and frequencies. This threshold voltage increases as the conditions become less favorable. Expressions are given for the values of the oscillations as functions of the voltage when the threshold is exceeded. When the sum frequency is absent, the energies dissipated at the plate and difference frequencies are in the ratio of the two frequencies. The oscillations described represent a special case of a class of similar oscillations, all of which depend on the presence of a non-linear reactance. Another special case is a molecular model capable of reproducing the main features of the Raman effect.
34 citations
TL;DR: In this article, an optimum proportioning for a wide variety of types of individually shielded circuits including several novel types designed to make the high-frequency attenuation low in comparison with the cross-sectional area occupied by the circuit, and the attenuation of different types is compared.
Abstract: For given conditions of design there exists an optimum proportioning or configuration which makes the high-frequency attenuation of a given type of individually shielded circuit a minimum. Determination is made of such optimum proportioning for a wide variety of types of individually shielded circuits including several novel types designed to make the high-frequency attenuation low in comparison with the cross-sectional area occupied by the circuit, and the attenuation of different types is compared. The following topics and specific circuit structures are considered: Coaxial Circuits — Basic Coaxial Circuit; Effect of Dielectric; Effect of Frequency on Optimum Ratio; Thin Walls; Stranded Conductors; Optimum Proportioning as a Function of Conductor Resistance. Balanced Shielded Circuits — Shielded Pair (Cylindrical Conductors and Shield) — Condition for Minimum Attenuation, Condition for Maximum Characteristic Impedance, Effect of Dielectric, Effect of Frequency; Pair in Space; Shielded Stranded Pair; Pair with Shield Return; Double Coaxial Circuit; Shielded Pair (Round Conductors and Oval Shield); Shielded Pair (Quasi-Elliptical Conductors); Shielded Quad.
22 citations
TL;DR: In this article, the authors studied an oscillating electromechanical system in which mechanical vibrations are sustained at a frequency near the resonant frequency of a mechanical system and electrical oscillations at the difference between the frequency of the mechanical vibration and that of the impressed force.
Abstract: Experimental results are given on an oscillating electromechanical system in which, under a single frequency impressed electromotive force, mechanical vibrations are sustained at a frequency near the resonant frequency of the mechanical system and electrical oscillations at the difference between the frequency of the mechanical vibration and that of the impressed force. The system is the one studied analytically by R. V. L. Hartley in an accompanying paper. Its performance conforms to the principal operating features predicted in his analysis.
14 citations
TL;DR: In this article, it is shown that corrosion of cable sheathing in conduit occurs by means of the operation of small corrosion cells on the surface of the sheath or by the leakage of current from the cable to ground.
Abstract: This paper discusses the corrosion of cable sheathing in the aerial and underground cable plants. Corrosion does not appear to be a primary factor affecting the life of aerial cables; failure of these cables occurs usually from intergranular embrittlement and is minimized by the use of alloy sheathing. It is shown that corrosion of cable sheathing in conduit occurs by means of the operation of small corrosion cells on the surface of the sheath or by the leakage of current from the sheath to ground. The driving force of these corrosion cells arises from some chemical inhomogeneity in either the metal or the surrounding environment. The course and the character of corrosion is determined chiefly by the influence of the constituents of the environment on the operation of these cells. These constituents may be classed as corroding or protective; — the corroding including oxygen, nitrates, alkalies and organic acids, while the protective are silicates, sulfates, carbonates, soil colloids and certain organic compounds. Cable sheathing buried directly in soils is seriously corroded by differential aeration-cell action resulting from physical contact of relatively large soil particles and metal. In general it is concluded that corrosion of cable sheathing is influenced more by the nature of the environment than by the chemical composition of the metallic material. The incidence of corrosion of cable sheathing is small owing to the maintenance of non-corrosive chemical and electrical environments in the cable plant.
6 citations
TL;DR: In this paper, it was shown that the equivalent network of negative-grid vacuum tubes both at low and at very high frequencies may be expressed in many different forms. And the advantages of two of them are described in some detail.
Abstract: It is shown that the equivalent network of negative-grid vacuum tubes both at low and at very high frequencies may be expressed in many different forms. Several are suggested and the advantages of two are described in some detail. One of these is closely analogous to that which is in general use at low frequencies and requires only the addition of resistive components in series both with the cathode-grid and the grid-plate capacitances to make it applicable to frequencies where transit time effects are appreciable though moderately small. The resistance in series with the grid-plate capacitance is negative in sign. In this form of the equivalent network, electron transit times do not introduce a phase angle into the amplification factor. The paper is divided into two parts. The first gives a descriptive interpretation of the results while the second contains the mathematical manipulations.
TL;DR: The discovery of the loadstone and some of its magnetic properties is now reputed to be some three thousand years old as discussed by the authors, and advances in theory have been particularly rapid during the last five or ten years; the author describes in this paper what he regards as the high points of this progress.
Abstract: DISCOVERY of the loadstone and some of its magnetic properties is now reputed to be some three thousand years old. During these many years ferromagnetism has resisted very successfully the attack of theorists, and even at the present time theory lags far behind experiment. But advances in theory have been particularly rapid during the last five or ten years; the author describes in this paper what he regards as the high points of this progress.
TL;DR: In this paper, the requirements and control of the wire system necessary to prevent imperfections in the picture and to permit switching of sending and receiving stations are discussed, as well as the new machines used to send and receive photographs are described.
Abstract: Transmission of photographs over telephone wires was begun commercially several years ago, but recent improvements have increased to 11 by 17 inches the size of photograph that could be transmitted and have made it possible for the picture to give much more information. The new machines used for sending and receiving photographs are described in this paper, and the requirements and control of the wire system necessary to prevent imperfections in the picture and to permit switching of sending and receiving stations are discussed.
TL;DR: In this paper, the application of electrochemical methods to corrosion investigations is discussed, and the position of the potential of a metal against its environment and the trend of this potential with time is discussed.
Abstract: This paper outlines the application of electrochemical methods to corrosion investigations. It discusses the position of the potential of a metal against its environment and the trend of this potential with time, pointing out that it is thereby possible to determine whether the corrosion process is controlled by reactions occurring at the anodic areas, the cathodic areas, or both; that is, whether there is a tendency toward passivity, inhibition or progressive attack. Measurements of film stability whether in terms of the leakage current which may be passed through the film or in terms of the amount of film forming material required to produce passivity or the amount of film destroying material required to render a metal active, furnish information as to the quality of corrosion resistant films. Measurements of the rate at which a film forms on a metal when placed in a film-forming environment throws light on its relative surface reactivity, and such information is of assistance in determining the rate of corrosion in homogeneous corrosive environments or the rate of passivation in the film-forming environments. On the basis of such measurements and with a chemical knowledge of the environments in which metals are used as well as the composition and physical state or structure of the metals, it is possible to predict corrosion behavior and to obtain an understanding of corrosion problems usually not possible by ordinary empirical corrosion tests.
TL;DR: This joint investigation at the College of Physicians and Surgeons of Columbia University was initiated in the hope of obtaining some of the needed data on the limits of dangerous electric shock.
Abstract: AS a basis for the development of protective measures and practices, knowledge of the limits of dangerous electric shock is obviously important and this joint investigation at the College of Physicians and Surgeons of Columbia University was initiated in the hope of obtaining some of the needed data. In seeking a value of current which if exceeded would be dangerous to man, it is important to consider for different practical conditions the effects which are brought about as the current is increased. The threshold of sensation is reached at about one milliampere for a frequency of 60 cycles. Other investigators have found that at about 15 milliamperes from hand to hand the subject becomes unable to control the muscles subjected to stimulation.
TL;DR: In this article, the decay of creosoted southern pine poles with coal tar creosotes has been investigated and over 3000 such poles were evaluated at thirteen creosoting plants in the South to determine when and where decay started.
Abstract: Poor penetration of the non-durable sapwood is the most important factor in the decay of creosoted southern pine poles. Over 3000 such poles that had been treated with coal tar creosotes of varying types at thirteen creosoting plants in the South have been critically inspected to determine when and where decay started. The poles had been in line from five to twenty-six years under widely diverse climatic conditions in scattered localities east of the Mississippi River. Ninety-five per cent of the failures were poles in which the creosote had penetrated less than 1.8 inches and 60 percent of the sapwood thickness. No failures were found in poles that had been penetrated more than 2.1 inches and 75 per cent of the sapwood thickness. The current Bell System treating specifications require a penetration of 2.5 inches or 85 per cent of the sapwood thickness. The hazard of failure by decay during the ordinary service life of a line is reduced to a practical minimum in poles produced under these specifications.
TL;DR: In this paper, a moving coil microphone is described which responds uniformly over a wide frequency range to sound arriving from any direction, and an acoustic screen has been developed which diminishes diffraction to an extent necessary to make the change in response due to angle of sound incidence imperceptible to the ear.
Abstract: A moving coil microphone is described which responds uniformly over a wide frequency range to sound arriving from any direction. A study of diffraction, the main factor causing directivity of microphones of the pressure type, leads to the conclusion that a small spherical shape is the most desirable for a non-directional microphone. But even fulfilling this requirement in the design of the housing leaves a large directional effect. Hence an acoustic screen has been developed which diminishes diffraction to an extent necessary to make the change in response due to angle of sound incidence imperceptible to the ear. The non-directional microphone is of simple and rugged construction. Adequate precautions have been taken to prevent atmospheric changes from affecting the stability. The small size and unusual shape of the microphone contribute much to its attractive appearance.
TL;DR: Improvements in transformers used in communication circuits are discussed in this paper, achieved partly through advances in design and partly through improvements in the constituent materials.
Abstract: The rapidly advancing art of electrical communication and the increasingly wide variety of its applications have required marked improvements in the transformers used in communication circuits. These improvements, achieved partly through advances in design and partly through improvements in the constituent materials, are discussed in this paper.
TL;DR: In this paper, a general relation between the percentage lost circuit time and transmission improvement in decibels was obtained from empirical measurements of noise-to-signal ratio made during the routine operation of short-wave radio telephone circuits.
Abstract: From empirical measurements of noise-to-signal ratio made during the routine operation of short-wave radio telephone circuits there is obtained a general relation between percentage lost circuit time and transmission improvement in decibels. In this relation “percentage lost circuit time” is the percentage of time that the noise-to-signal ratio is considered unsatisfactory. No attempt is made to define such a standard quantitatively. If, from past experience with a long-range, short-wave telephone, telegraph or broadcast circuit, it is known that the circuit is unsatisfactory a certain percentage of the time, the above-mentioned relation may be used to estimate the effect of transmission improvement upon this percentage of unsatisfactory or lost time. For a given circuit the variation in percentage lost circuit time, as the standard for the tolerable service is changed by a given number of decibels, may also be estimated. There are included estimates of the relation between the number of lost time intervals of various lengths and transmission improvement.
TL;DR: Tandem operation is becoming of increasing importance in the Bell System and the operating and service features of the different types, and the conditions under which each type is used, are outlined in this paper.
Abstract: Tandem operation is becoming of increasing importance in the Bell System. The operating and service features of the different types, and the conditions under which each type is used, are outlined. Charts are included showing, schematically, typical trunking arrangements in the various systems. The increasing use of tandem operation on traffic handled at toll boards is discussed.
TL;DR: In this paper, the variations in long-wave radio field strength near the time of sunset on long transmission paths, which have been reported by many observers, were studied for the purpose of formulating rational methods of forecasting their time of occurrence.
Abstract: The variations in long-wave radio field strength near the time of sunset on long transmission paths, which have been reported by many observers, were studied for the purpose of formulating rational methods of forecasting their time of occurrence. During some preliminary observations fair agreement was found between the time of minimum field and the sun's position relative to a particular point on the transatlantic path under observation. The more extended study of radio field variations during sunset periods and solar eclipses disclosed that in general no exact relationship could be established between the sun's position at any point and the occurrence of the minimum field. Observations of field variations were made on radio signals at a number of different frequencies and over several paths. It was concluded that a characteristic sunset cycle of field variations is present on frequencies between 18 kc. and 68 kc. for transmission paths longer than 700 km. For paths less than 200 km. long, such variations are negligible. There is some evidence that the amplitude of these field variations is smaller at lower frequencies. Analysis of the data presented indicates that long waves over long paths are transmitted predominately by “sky waves.” From the data it was not possible to establish any satisfactory picture of the path followed. It was established, however, that empirical methods based on observations over a particular transmission path may be employed to forecast the approximate time of occurrence of field variations.
TL;DR: In this article, the authors present an expansion by means of which the evaluation of a high order function can be readily accomplished with a considerable degree of accuracy, and the development of the expansion is prefaced by some remarks on the early history of the Hermitian functions and the relation of this history to modern theoretical physics.
Abstract: Among the wide variety of practical and theoretical problems confronting the telephone engineer, there is a surprisingly large number to whose solution mathematics has made notable contribution. In his kit of mathematical tools the theory of probability is a frequently used and most effective instrument. This theory of probability contains a large number of theorems, a large number of functions, which permit of application to telephony. Among these is a particular tool, a particular group of mathematical functions known as the “Hermitian Functions,” each of which is identified by a number called its “order.” These mathematical functions or relations have no practical utility until the variables in the equation can be assigned numerical values and the resultant numerical value of the function calculated. Tables of the numerical values of Hermitian functions of low order exist; for example, Glover's Tables of Applied Mathematics cover the ground for those of the first eight orders. But tables for the functions of higher order are still a desideratum. This paper presents an expansion by means of which the evaluation of a high order function can be readily accomplished with a considerable degree of accuracy. The development of the expansion is prefaced by some remarks on the early history of the Hermitian functions and the relation of this history to modern theoretical physics.
TL;DR: In this paper, the earth resistivity is used to estimate low-frequency ground-return mutual impedances between power and communication lines, and the resistivities of the component parts of the earth's crust and the arrangement of these parts are taken into account.
Abstract: N connection with inductive coordination problems it is frequently necessary to estimate low-frequency ground-return mutual impedances between power and communication lines. The distribution of currents in the earth is a major factor in the determination of these impedances. This distribution is controlled by the resistivities of the component parts of the earth's crust and the arrangement of these parts. In impedance formulas that are customarily used the effect of the earth is taken care of by the inclusion of a single parameter — the earth resistivity. For a homogeneous earth this would be the actual resistivity of the material composing it. But the crust is nowhere homogeneous; hence, the resistivity used in such formulas is always of the nature of an average of the resistivities of the several parts of the crust — it is termed the effective earth resistivity.
TL;DR: The Heaviside operational calculus postulates at the outset that the initial (boundary) conditions at reference time t = 0 are those of equilibrium; that is to say, the system is at rest when suddenly energized at time T = 0 by a unit impressed force as mentioned in this paper.
Abstract: THE Heaviside operational calculus postulates at the outset that the initial (boundary) conditions at reference time t = 0 are those of equilibrium; that is to say, the system is at rest when suddenly energized at time t = 0 by a “unit” impressed force. By unit impressed force is to be understood a force which is zero before, unity after, time t = 0.
TL;DR: A brief description of the principle of operation of teletypewriters is included in this paper as an introduction to the discussion of the transmission requirements and the plan of the present system.
Abstract: A nationwide transmission system has been established in the United States for teletypewriter exchange service by means of which 2-way communication between teletypewriter subscribers can be established in a time comparable to that required for long distance telephone service. A brief description of the principle of operation of teletypewriters is included in this paper as an introduction to the discussion of the transmission requirements and the plan of the present system.
TL;DR: The applications made by the Bell Telephone Laboratories of microanalytical and related special techniques to communication research and engineering are discussed.
Abstract: Analysis was beginning to take its place as an important branch of chemistry when, in 1828, Wohler synthesized urea and the Age of Synthetic Organic Chemistry was born, destined to overshadow analysis for nearly a century. When interest in synthesis began to diminish, in the late 1800's, physical chemistry arose to intrigue the chemical mind. The analyst, thus neglected, had to work with apparatus, techniques and viewpoints evolved for other chemical purposes. In 1910 the Austrian Pregl found it necessary to analyze a sample too small for the then available technique to handle. His solution was the invention of a new kind of analysis — microanalysis, the essential features of which are: reduction of apparatus size and of scale of operations to a point commensurate with sample size; development of entirely new techniques, apparatus and chemical reactions specially suited to analysis; and inculcation in the mind of the analyst of the attitude that analytical problems are, in greater or less degree, research problems, and are to be approached as such, with a mind entirely unrestricted by chemical classicism. This article discusses the applications made by the Bell Telephone Laboratories of microanalytical and related special techniques to communication research and engineering.
TL;DR: In this paper, the authors concluded from measurements of virtual heights and critical ionization frequencies of the various regions of the ionosphere which were made during two solar eclipses at Deal, New Jersey, that ultra-violet light is an important ionizing agency in the E, M, F 1, and F 2 regions.
Abstract: It is concluded from measurements of virtual heights and critical ionization frequencies of the various regions of the ionosphere which were made during two solar eclipses at Deal, New Jersey, that ultra-violet light is an important ionizing agency in the E, M, F 1 , and F 2 regions.
TL;DR: In this paper, the appearance of an electromotive force at the terminals of a vibrating rod or wire of magnetic material was investigated and it was concluded from experiments somewhat more simple and direct than those employed by other investigators that the effect was due to changes in the state of circular magnetization accompanying the variations of stress
Abstract: The appearance of an electromotive force at the terminals of a vibrating rod or wire of magnetic material was investigated It was concluded from experiments somewhat more simple and direct than those employed by other investigators that the effect was due to changes in the state of circular magnetization accompanying the variations of stress The results suggested problems for more intensive investigation and applications of possible practical value