Showing papers in "Bell System Technical Journal in 1938"
TL;DR: This paper calls attention to the practical value of a more extended use of the impedance concept, which brings out a certain underlying unity in what otherwise appear diverse physical phenomena.
Abstract: This paper calls attention to the practical value of a more extended use of the impedance concept. It brings out a certain underlying unity in what otherwise appear diverse physical phenomena. Although an attempt has been made to trace the history of the concept of “impedance” and many interesting early suggestions have been found, reference to these lies beyond the scope of this paper. Apparently, Sir Oliver Lodge was the first to use the word “impedance,” but the concept has been developed gradually as circumstances demanded through the efforts of countless workers. The main body of the paper is divided into three parts: Part I, dealing with the exposition of the impedance idea as applied to different types of physical phenomena; Part II, in which the general formulae are deduced for reflection and transmission coefficients; Part III, presenting some special applications illustrating the practical utility of the foregoing manner of thought.
184 citations
TL;DR: In this article, the potential distribution, current, and electron transit time resulting from the perpendicular injection of electrons into the space between parallel planes is considered, where electrons are assumed to be injected uniformly with velocities corresponding to the potential of the plane through which they are injected.
Abstract: The problem of the potential distribution, current, and electron transit time resulting from the perpendicular injection of electrons into the space between parallel planes is considered The electrons are assumed to be injected uniformly with velocities corresponding to the potential of the plane through which they are injected Consideration of all possible solutions of the basic equation shows that four general types of potential distribution are possible Curves are given which enable the easy calculation of transmitted current and transit time and show the complete potential distribution for any concrete example The case for current injected through both planes is also considered The complete mathematical treatment is given in the appendix
133 citations
TL;DR: These quantities, as determined by the presence or absence of speech energy, have been measured from continuous oscillograms of calls on a New York-Chicago telephone circuit used for Bell System business, and the results of statistical analyses of these data are presented.
Abstract: Two-way conversation is arbitrarily defined in terms of vocal intervals and the pauses between them. These quantities, as determined by the presence or absence of speech energy, have been measured from continuous oscillograms of calls on a New York-Chicago telephone circuit used for Bell System business, and the results of statistical analyses of these data are presented.
85 citations
TL;DR: The theoretical analysis of the effect of space charge upon the shot noise in a planar diode has been studied in this article, showing that the tube noise is equivalent to the thermal resistance noise of the plate resistance at 0644 times the cathode temperature.
Abstract: The theoretical analysis of the effect of space charge upon the “shot noise” in a planar diode shows that for practically all operating conditions, the tube noise is equivalent to the thermal resistance noise of the plate resistance at 0644 times the cathode temperature Noise in diodes of other than planar shapes is discussed and it is concluded that the same relation holds It is shown that transit time produces the same high frequency modification for both the thermal and shot tube noise, and that the tube noise is decreased by transit time
78 citations
Journal Article•
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TL;DR: The use of equalizing structures to compensate for the variation in the phase and attenuation characteristics of transmission lines and other pieces of apparatus is well known in the communication art as discussed by the authors.
Abstract: The use of equalizing structures to compensate for the variation in the phase and attenuation characteristics of transmission lines and other pieces of apparatus is well known in the communication art. Ordinarily, of course, an equalizer has a definite characteristic fixed by the apparatus with which it is to be associated. It may happen, however, that the characteristics demanded of the equalizer cannot be prescribed in advance, either because the characteristics of the associated apparatus are not known with sufficient precision, or because they vary with time. Examples are found in the equalization of transmission lines the exact lengths of which are unknown, or the characteristics of which may be affected by changes in temperature and humidity.
78 citations
TL;DR: In this article, the authors developed a high pass, impedance transforming filter for the exponential transmission line and proved that the deviation of the exponential line from an ideal impedance transformer may be decreased by an order of magnitude by shunting the low impedance end with an inductance and inserting a capacitance in series with the high impedance end.
Abstract: The theory of the exponential transmission line is developed. It is found to be a high pass, impedance transforming filter. The cutoff frequency depends upon the rate of taper. The deviation of the exponential line from an ideal impedance transformer may be decreased by an order of magnitude by shunting the low impedance end with an inductance and inserting a capacitance in series with the high impedance end. The magnitudes of these reactances are equal to the impedance level at their respective ends of the line at the cutoff frequency. For a two-to-one impedance transformer the line is 0.0551 wave-lengths long at the cutoff frequency. For a four-to-one impedance transformer the line is 0.1102 wave-lengths long at the cutoff frequency, etc. The results have been verified experimentally. Practical lines 50 meters and 15 meters long have been constructed which transform from 600 to 300 ohms over the frequency range from 4 to 30 mc. with deviations from the ideal that are small compared with the deviations from the ideal of commercial transmission lines, either two-wire or concentric. When an exponential line is used as a dissipative load of known impedance instead of a uniform line it is possible to approach more nearly the ideal of constant heat dissipation per unit length. This makes it possible to use a shorter line.
53 citations
TL;DR: In this paper, a 12-channel telephone system for existing cables is described, which incorporates a number of interesting departures from the previous carrier art, and is now being manufactured in considerable quantities to meet increased traffic requirements.
Abstract: A new 12-channel carrier telephone system for existing cables is described. This system, which incorporates a number of interesting departures from the previous carrier art, is now being manufactured in considerable quantities to meet increased traffic requirements.
19 citations
TL;DR: In this paper, an ultra-short-wave fading study was carried out in the range of 1.6 to 5.0 meters over a 70 mile (112.6 kilometer) ocean path, on 106 days during a period of two years.
Abstract: Results of an ultra-short-wave fading study are here reported. Transmission was carried out in the range of 1.6 to 5.0 meters, over a 70 mile (112.6 kilometer) ocean path, on 106 days during a period of two years. Both horizontal and vertical polarizations were used and during part of the time a 6-megacycle amplitude, 120-cycle, frequency modulated transmission was added, for the cathode-ray tube observation of the frequency characteristics of the radio path. On 45 mornings records were taken, on vertically polarized radiations, during the flight period of the Mitchel Field Weather Bureau plane. Fading was found present practically all of the time. Amplitude changes up to 40 db and fading rates up to 5 fades per minute were found. Simultaneous transmission of the same wave in two polarizations, and of two waves of different wave-length in the same polarization showed that the horizontally polarized component was practically always, and the shorter wave-length one was usually the worse fader of the pair. The greater part of the time there was no correlation between the fading of these radiation pairs; occasionally, however, and for the slow, smooth amplitude, undulating type of fading, coincidence was observed. The frequency sweep patterns showed multiple signal components to be present, with various degrees of relative phase retardation. A tentative explanation is proposed for these phenomena. This theory assumes the presence of a refracted-diffracted signal component, transmitted along the earth's surface and calculable in the manner of Wwedensky, Van der Pol and Gray, and one or more signal components reflected from air mass boundaries. The airplane results are shown to be in reasonable agreement with the frequency sweep observations. Boundary heights from 5.5 kilometers down to 1.9 kilometers are measured; below 1.9 kilometers other boundaries are indicated. The receiver band, flat over two megacycles, sets the low height limit of resolution of reflecting boundaries at 1.9 kilometers. Most of the boundaries are at the lower heights.
18 citations
TL;DR: In this paper, the Fourier series analysis is performed by a direct evaluation of the integrals which form the coefficients in a Fourier Series, and the results are theoretically exact in the sense that the measurement of each harmonic is independent of the other harmonics which may be present in the function.
Abstract: An instrument which makes a Fourier Series Analysis of a function by optical means has recently been completed. The function to be analyzed is supplied in the form of a variation in the density or in the width of the transparent portion of a photographic film. The analysis is performed by a direct evaluation of the integrals which form the coefficients in a Fourier Series, and the results are theoretically exact in the sense that the measurement of each harmonic is independent of the other harmonics which may be present in the function. The operation of the instrument is largely automatic, and is rapid enough so that 30 harmonics can be measured in about a minute and a half.1
18 citations
TL;DR: In this paper, the Ben Laboratories have been engaged for some time in the development of wire line circuits for transmitting television signals between studios and broadcasting transmitters, or between cities, as may some day be required if television follows in the footsteps of sound program broadcasting.
Abstract: The reports which have been made on the progress in television development increase the expectation that the broadcasting of visual programs witJ soon be realized. In anticipation of that result, the Ben Laboratories has been engaged for some time in the development of wire line circuits for transmitting television signals between studios and broadcasting transmitters, or between cities, as may some day be required if television follows in the footsteps of sound program broadcasting.
15 citations
TL;DR: That streams of electrons possess the properties of beams of waves was discovered early in 1927 in a large industrial laboratory in the midst of a great city, and in a small university laboratory overlooking a cold and desolate sea.
Abstract: That streams of electrons possess the properties of beams of waves was discovered early in 1927 in a large industrial laboratory in the midst of a great city, and in a small university laboratory overlooking a cold and desolate sea. The coincidence seems the more striking when one remembers that facilities for making this discovery had been in constant use in laboratories throughout the world for more than a quarter of a century. And yet the coincidence was not, in fact, in any way remarkable. Discoveries in physics are made when the time for making them is ripe, and not before; the stage is set, the time is ripe and the event occurs--more often than not at widely separated places at almost the same moment.
TL;DR: In this article, the frequency controlling resonant element is used as one arm of a Wheatstone resistance bridge, which is kept in balance automatically by a thermally controlled arm, providing constancy of output amplitude, purity of wave form, and stabilization against fluctuations in power supply or changes in circuit elements.
Abstract: A new type of constant frequency oscillator of very high stability is presented. The frequency controlling resonant element is used as one arm of a Wheatstone resistance bridge. Kept in balance automatically by a thermally controlled arm, this bridge provides constancy of output amplitude, purity of wave form, and stabilization against fluctuations in power supply or changes in circuit elements. A simple one-tube circuit has operated consistently with no short-time frequency variations greater than ± 2 parts in 108. Convenient means are provided for making precision adjustments over a narrow range of frequencies to compensate for long-time aging effects. Description of the circuit is followed by a brief linear analysis and an account of experimental results. Operating records are given for a 100 kc. oscillator.
TL;DR: In this paper, the authors describe magnetic shielding in general and give a theoretical analysis of the shielding efficiency of cylindrical shells for steady and alternating magnetic fields, with experimental information on various types of transformer shields.
Abstract: The first part of this article is a descriptive discussion of magnetic shielding in general. Formulae are then given for the calculation of shielding efficiency of cylindrical shells for steady and alternating magnetic fields. By means of these formulae the shielding efficiency for various types of cylindrical shields has been calculated for a steady magnetic field. The second part of the article contains experimental information on various types of transformer shields. This information supplements the theory in connection with factors which would be very laborious to treat theoretically. The theory and the experimental data are coordinated in such a manner that the shielding efficiency of a particular shield can be calculated with an accuracy which is sufficient for practical purposes.
TL;DR: In this article, the authors present the evidence for this, as obtained by comprehensive laboratory and field tests, together with a discussion of the factors responsible for this superior performance and of the consideration involved in its appraisal.
Abstract: The new telephone instruments now being introduced by the Bell System result in an outstanding improvement in transmission performance in service. The evidence for this, as obtained by comprehensive laboratory and field tests, is presented here together with a discussion of the factors responsible for this superior performance and of the consideration involved in its appraisal.
TL;DR: Transmitters and receivers for use at subscribers' telephone stations have been designed which not only materially improve transmission but also simplify manufacture and facilitate maintenance as mentioned in this paper. But these improvements have not yet been considered in the general public.
Abstract: Transmitters and receivers for use at subscribers' telephone stations have been designed which not only materially improve transmission but also simplify manufacture and facilitate maintenance. This paper discusses these improvements and describes some of the new design technique employed in their development.
TL;DR: In this article, the channel selecting filters used at the terminals of the twelve-channel cable carrier system are the principal filters in the system and their importance is evident from the fact that they represent over one-third of the cost of the system terminals.
Abstract: Since the channel selecting filters used at the terminals of the twelve-channel cable carrier system are the principal filters in the system this paper is concerned primarily with these. Their importance is evident from the fact that they represent over one-third of the cost of the system terminals.
TL;DR: The circuits, performance and equipment features of the terminals of a new 12-channel carrier system for application to existing toll cables are described.
Abstract: This paper describes the circuits, performance and equipment features of the terminals of a new 12-channel carrier system for application to existing toll cables. The 12-channel group of terminal apparatus has been designed also to form a basic part of the terminals of other carrier systems now under development, such as the type J system for open wire and the coaxial system.
TL;DR: The art of controlling the amplitude range of telephone signals involves recognition of certain characteristics in addition to those used to specify the performance of ordinary transducers, such as the steady state input-output characteristics, time actions, and the range over which they function.
Abstract: The art of controlling the amplitude range of telephone signals involves recognition of certain characteristics in addition to those used to specify the performance of ordinary transducers. Fundamentally, three kinds of characteristics are necessary to distinguish different range control devices. They are (1) the steady-state input-output characteristics, (2) the time actions, and (3) the range over which they function. In some cases, several secondary characteristics may be of interest, but they need not be considered in determining to which class a particular device belongs. This paper discusses and classifies these characteristics.
TL;DR: The Type H single channel carrier telephone system described in the following paper is designated the Type H. It is characterized by several new features, making it applicable not only to the needs of telephone companies but also to those of railroads, power systems and oil companies as discussed by the authors.
Abstract: The single channel carrier telephone system described in the following paper is designated the Type H. It is characterized by several new features, making it applicable not only to the needs of telephone companies but also to those of railroads, power systems and oil companies. It replaces the Type D single channel carrier system, more than 500 of which are now in operation in the Bell System, and, in addition because of its lower cost is applicable to shorter distances. It therefore marks another step in extending the use of carrier. Reduction in size and provision for operating on a-c supply simplify its installation, and its portability makes it well suited to provide emergency circuits.
TL;DR: A family of devices which automatically respond to signals and control the circuit amplification in such a way as to improve transmission is described.
Abstract: This paper describes a family of devices which automatically respond to signals and control the circuit amplification in such a way as to improve transmission. Their general characteristics are outlined, their differences explained, and some of their applications are listed.
TL;DR: The fundamental principles and various features of the teletypewriter machines now in common use are discussed and the more important factors which have been controlling in their development are explained.
Abstract: During the past few years the use of teletypewriters has become quite extensive in the Bell System. Simpler and cheaper machines have recently been made available for meeting the simpler service requirements and attachments have been designed to provide additional features for meeting more complex service requirements. This article discusses the fundamental principles and various features of the teletypewriter machines now in common use and explains the more important factors which have been controlling in their development.
TL;DR: In this paper, it was shown that the electrical power output of a telephone transmitter may be more than a thousand times as great as the acoustic power activating it, and that this greatly augmented power is dissipated in the circuit of the telephone set; part is impressed upon the telephone line, whence it is propagated on to the distant listener; and part finds its way into the receiver of the same set, where it is reconverted into sound waves.
Abstract: The telephone transmitter serves to convert sound waves into their electrical facsimile; but in performing this primary function the transmitter also acts as an amplifier. Under some conditions the electrical power output of a transmitter may be more than a thousand times as great as the acoustic power activating it. Part of this greatly augmented power is dissipated in the circuit of the telephone set; part is impressed upon the telephone line, whence it is propagated on to the distant listener; and part finds its way into the receiver of the same set, where it is reconverted into sound waves. Speech or noise, picked up by the transmitter and reproduced by the receiver of the same set, is caned sidetone.
TL;DR: Applications of high speed motion picture photography to a variety of problems associated with the design of telephone apparatus, related to the development of relays, switches, clutches, ringers, dials, coin collector mechanisms, contact conditions, materials testing, etc. are given.
Abstract: A motion picture camera used in taking 4000 pictures per second is described. Applications of high speed motion picture photography to a variety of problems associated with the design of telephone apparatus are given. The resulting pictures in “slow motion” permit convenient and accurate analysis of space-time relationships of mechanical parts in motion otherwise too rapid to be perceived because of their transient nature. This work has related to the development of relays, switches, clutches, ringers, dials, coin collector mechanisms, contact conditions, materials testing, etc. It has been applied to studies of noise reduction in mechanisms and to research problems associated with the production of speech by the vocal cords.
TL;DR: The development of spectroscopy is traced through Newton, Fraunhofer and Kirchoff to Hartley, Pollock and Leonard, and De Gramont who, in the period 1880-1920, applied the spectroscope to chemical analysis as discussed by the authors.
Abstract: The development of spectroscopy is traced through Newton, Fraunhofer and Kirchoff to Hartley, Pollock and Leonard, and De Gramont who, in the period 1880–1920, applied the spectroscope to chemical analysis. It is shown that modern quantitative spectrochemical analysis began with the comparison standard method of Meggers in 1922, and developments since that time are discussed. The organization and functioning of the spectrochemical unit of the analytical group at the Bell Telephone Laboratories is described, and a number of examples of applications to telephone problems are given.
TL;DR: In this paper, a brief description of the existing and the new arrangements for transmission measurement on telephone circuits is given. But this is not a complete survey of all the existing arrangements.
Abstract: Transmission measurements on telephone circuits have long been recognized as essential aids in the furnishing of good service. Recent development work has produced new testing methods and apparatus which greatly simplify and expedite transmission measuring. This paper gives a brief description of the existing and the new arrangements.
TL;DR: In this paper, the authors present a cable carrier system for Toll Cables, which limits the number of channels which can be utilized in anyone cable, not only by limiting the channel number of a single pair, but also by limiting number of pairs that can be used.
Abstract: Crosstalk and noise are important factors in cable carrier transmission as outlined in the paper “A Carrier Telephone System for Toll Cables” by Messrs. C. W. Green and E. I. Green. Crosstalk and noise limit the number of carrier channels which can be utilized in anyone cable, not only by limiting the number of channels which can be placed on a single pair, but by limiting the number of pairs which can be used. Noise also. controls the transmission loss which can be permitted between repeaters. Without the crosstalk and noise reduction measures described in this paper, the number of carrier channels per cable would be so few and the spacing between repeaters so short, that the type K carrier system would be impracticable.
TL;DR: In this article, a mathematical analysis of the conditions for the constant frequency of the vacuum tube oscillator under changes of electrode potentials or of the cathode temperature is presented, which are independent of particular circuit configurations and are applicable to certain dissipative circuits as well as to purely reactive systems.
Abstract: The author presents a mathematical consideration of the conditions which insure constant frequency of the vacuum tube oscillator under changes of electrode potentials or of the cathode temperature. It has already been shown that the grid and plate resistances may enter into the determination of the frequency. The problem is treated here in the manner suggested in the recent studies of feedback amplifiers. The conditions necessary for stability are developed in terms which are independent of particular circuit configurations and are applicable to certain dissipative circuits as well as to purely reactive systems.
TL;DR: The time factor in telephone transmission has been studied in this paper, where it is shown that the occurrence of lockout caused by the echo suppressors involved in a long telephone connection causes an increase in the repetition rate.
Abstract: “The Time Factor in Telephone Transmission” by O. B. Blackwell (B. S. T. J. January 1932) deals with a number of problems which arise in connection with telephone circuits having long transmission times. This paper discusses one such effect, the occurrence of lockout caused by the echo suppressors involved in a long telephone connection. The occurrence of lockout is shown to cause an increase in repetition rate, which is ordinarily small for circuits as now used commercially. The increase in repetition rate is approximately proportional to the number of lockouts occurring and to their mean duration, or to the per cent of time locked out. The expected number of lockouts is shown to depend upon the characteristic time intervals of conversational speech, the relay hangovers, the delay of the circuit and location of the echo suppressors with respect to the ends of the circuit. Subject to certain restrictions, the expected number of lockouts increases with the delay included between the echo suppressors, and is nearly independent of the delays between the suppressors and the circuit terminals. The mean duration of lockouts is shown to be proportional to the relay hangovers.