Showing papers in "Bell System Technical Journal in 1957"
TL;DR: In this paper, the basic problem of interconnecting a given set of terminals with a shortest possible network of direct links is considered, and a set of simple and practical procedures are given for solving this problem both graphically and computationally.
Abstract: The basic problem considered is that of interconnecting a given set of terminals with a shortest possible network of direct links Simple and practical procedures are given for solving this problem both graphically and computationally It develops that these procedures also provide solutions for a much broader class of problems, containing other examples of practical interest
4,395 citations
TL;DR: In this article, the authors discuss some factors which limit the sensitivity of microwave paramagnetic resonance equipments and the results verified by measuring the signal-to-noise ratio with known amounts of a free radical.
Abstract: This paper discusses some factors which limit the sensitivity of microwave paramagnetic resonance equipments. Several specific systems are analyzed and the results verified by measuring the signal-to-noise ratio with known amounts of a free radical. The two most promising systems, especially at low powers, employ either superheterodyne detection or barretter homodyne detection. A detailed description of a superhetrodyne spectrometer is given.
364 citations
TL;DR: In this article, the quantizing error power is calculated as a function of the degree of companding, the number of quantizing steps, the signal volume, the size of the equivalent dc component, and the statistical distribution of amplitudes in the signal.
Abstract: Instantaneous companding may be used to improve the quantized approximation of a signal by producing effectively nonuniform quantization. A revision, extension, and reinterpretation of the analysis of Panter and Dite permits the calculation of the quantizing error power as a function of the degree of companding, the number of quantizing steps, the signal volume, the size of the “equivalent dc component”' in the signal input to the compressor, and the statistical distribution of amplitudes in the signal. It appears, from Bennett's spectral analysis, that the total quantizing error power so calculated may properly be studied without attention to the detailed composition of the error spectrum, provided the signal is complex (such as speech or noise) and is sampled at the minimum information-theoretic rate. These calculations lead to the formulation of an effective process for choosing the proper combination of the number of digits per code group and companding characteristic for quantized speech communication systems. An illustrative application is made to the planning of a hypothetical PCM system, employing a common channel compandor on a time division multiplex basis. This reveals that the calculated companding improvement, for the weakest signals to be encountered in such a system, is equivalent to the addition of about 4 to 6 digits per code group, i.e., to an increase in the number of uniform quantizing steps by a factor between 24 = 16 and 26 = 64 Comparison with the results of related theoretical and experimental studies is also provided
205 citations
TL;DR: In this article, the authors present a table for the smallest number of units required per process to be put on test to satisfy a given specification, where the experimenter chooses two constants d and P (0 < d ≦ 1; 0 ≦ P < 1) and specifies that he would like to guarantee a probability of at least P of a correct selection whenever the true difference between the yields associated with the best and second best processes is at least d.
Abstract: Tables have been prepared for use in any experiment designed to select that particular one of k binomial processes or populations with the highest (long time) yield or the highest probability of success. Before experimentation the experimenter chooses two constants d and P (0 < d ≦ 1; 0 ≦ P < 1) and specifies that he would like to guarantee a probability of at least P of a correct selection whenever the true difference between the longtime yields associated with the best and the second best processes is at least d. The tables show the smallest number of units required per process to be put on test to satisfy this specification. Separate tables are given for k = 2, 3, 4 and 10. Each table gives the result for d = 0.05 (0.05) 0.50 and for P = 0.50, 0.60, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, and 0.99. For values of d and P not considered in the tables, graphs are given on which interpolation can be carried out. Graphs have also been constructed to make possible an interpolation or extrapolation for other values of k. An alternative specification is given for use when the experimenter has some a priori knowledge of the processes and their probabilities of success. This specification is then compared with the original specification. Applications of these tables to different types of problems are considered.
119 citations
TL;DR: In this study people read words as fast as they were able to; from these results some deductions are made about the capacity of a human being as an information channel.
Abstract: The limitation on the rate at which information can be transmitted over an ordinary telephone channel is a human one. In this study people read words as fast as they were able to; from these results some deductions are made about the capacity of a human being as an information channel. The discrepancy between human channel capacity measured thus (40–50 bits/sec) and telephone and television channel capacity (about 50,000 bits/sec and 50,000,000 bits/sec respectively) is provocative.
117 citations
TL;DR: In this article, radio transmission theory and experiment in all frequency bands of current interest are summarized, including ground wave and sky wave transmission, and both line of sight and beyond horizon transmission are considered.
Abstract: The engineering of radio systems requires an estimate of the power loss between the transmitter and the receiver. Such estimates are affected by many factors, including reflections, fading, refraction in the atmosphere, and diffraction over the earth's surface. In this paper, radio transmission theory and experiment in all frequency bands of current interest are summarized. Ground wave and sky wave transmission are included, and both line of sight and beyond horizon transmission are considered. The principal emphasis is placed on quantitative charts that are useful for engineering purposes
115 citations
TL;DR: In this paper, a comprehensive theory with which the forces and motions of a submarine cable can be determined in typical laying and recovery situations is presented, where the effects of ship motion, varying bottom depth, ocean cross currents, and the problem of cable laying control are considered.
Abstract: This paper is an attempt to formulate a comprehensive theory with which the forces and motions of a submarine cable can be determined in typical laying and recovery situations. In addition to the fundamental case of a cable being laid or recovered with a ship sailing on a perfectly calm sea over a horizontal bottom, the effects of ship motion, varying bottom depth, ocean cross currents, and the problem of cable laying control are considered. Most of the results reduce to simple formulas and graphs. Their application is illustrated by examples.
83 citations
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TL;DR: A close-packed strictly e-error-correcting code on n, n > e, places cannot exist unless e of the coefficient vanish in (1 + x)e(1 − x)n−1−e when this is expanded as a polynomial in x.
Abstract: From the work of Shannon one knows that it is possible to signal over an error-making binary channel with arbitrarily small probability of error in the delivered information. The effects of errors produced in the channel are to be eliminated, according to Shannon, by using an error correcting code. Shannon's proof that such codes exist does not provide a practical scheme for constructing them, however, and the explicit construction and study of such codes is of considerable interest. Particularly simple codes in concept are the ones called here close packed strictly e-error-correcting (the terminology is explained later). It is shown that for such a code to exist, not only must a condition due to Hamming be satisfied, but also another condition. The main result may be put as follows: a close-packed strictly e-error-correcting code on n, n > e, places cannot exist unless e of the coefficient vanish in (1 + x)e(1 − x)n−1−e when this is expanded as a polynomial in x
80 citations
TL;DR: A set of codes based partially upon the Reed-Muller codes is described for correcting a number of errors in a more restricted class of message lengths for an arbitrary number of different signals.
Abstract: If a noisy channel is used to transmit more than two distinct signals, information may have to be specially coded to permit occasional errors to be corrected. If pulse amplitude modulation is used, the most probable error is a small one, e.g., 6 is changed to 7 or 5. Codes for correcting single small errors, and for correcting single small errors and detecting double small errors, in a message of arbitrary length, for an arbitrary number of different signals in the channel, are derived in this paper. For more specialized situations, the error is not necessarily restricted to a small value. Codes are derived for correcting any single unrestricted error in a message of arbitrary length for an arbitrary number of different signals Finally, a set of codes based partially upon the Reed-Muller codes is described for correcting a number of errors in a more restricted class of message lengths for an arbitrary number of different signals The described codes are readily implemented. Many techniques are used which have an analog in a binary system. Other techniques are broadly analogous to binary coding techniques or are special adaptations of a binary code.
72 citations
TL;DR: In this article, the propagation of short radio waves beyond the horizon is discussed in terms of reflection from layers in the atmosphere formed by relatively sharp gradients of refractive index, and the dependence of the propagation on path length, antenna size and wavelength is obtained.
Abstract: Propagation of short radio waves beyond the horizon is discussed in terms of reflection from layers in the atmosphere formed by relatively sharp gradients of refractive index. The atmosphere is assumed to contain many such layers of limited dimensions with random position and orientation. On this basis, the dependence of the propagation on path length, antenna size and wavelength is obtained.
71 citations
TL;DR: In this paper, it was shown that carbon from decomposition of organic vapors greatly alters the conditions under which an electric arc can be initiated and can be sustained, and that for many circuit conditions contacts activated by this carbon cannot be protected against severe arcing by any conventional capacitance-resistance network.
Abstract: Unreproducibility of earlier work on the erosion of relay contacts has been traced to the effects of organic vapors in the atmosphere. Carbon from decomposition of these vapors greatly alters the conditions under which an electric arc can be initiated and can be sustained. The importance from the standpoint of erosion comes from the fact that for many circuit conditions contacts activated by this carbon cannot be protected against severe arcing by any conventional capacitance-resistance network. This paper reports investigations which have enabled us to understand the activation of contacts by organic vapors.
TL;DR: In this article, generalized telegraphist's equations for all modes in a curved circular waveguide containing an inhomogeneous dielectric were derived, and criteria were set up for keeping the power levels of all spurious modes low in a compensated bend.
Abstract: Generalized telegraphist's equations are derived, following Schelkunoff, for all modes in a curved circular waveguide containing an inhomogeneous dielectric. Particular attention is paid to the coupling between the TE 01 mode and other modes in the curved guide. The results are applied to the problem of preventing the mode conversion from TE 01 to TM 11 which normally occurs in a curved round waveguide, by partially filling the cross section of the curved guide with a suitably shaped dielectric, such as polystyrene foam. Design equations are given for various compensators, and criteria are set up for keeping the power levels of all spurious modes low in a compensated bend. Dielectric losses, which may be important at millimeter wavelengths, are briefly treated. The potentialities of different compensator designs are illustrated by numerical examples.
TL;DR: In this paper, the effect of an applied torsion on a magnetic wire is to shift the preferred direction of magnetization into a helical path inclined at an angle of 45° with respect to the axis.
Abstract: Three methods have been developed for storing information in a coincident-current manner on magnetic wire. The resulting memory cells have been collectively named the “twistor”. Two of these methods utilize the strain sensitivity of magnetic materials and are related to the century old Wertheim or Wiedemann effects; the third utilizes the favorable geometry of a wire. The effect of an applied torsion on a magnetic wire is to shift the preferred direction of magnetization into a helical path inclined at an angle of 45° with respect to the axis. The coincidence of a circular and a longitudinal magnetic field inserts information into this wire in the form of a polarized helical magnetization. In addition, the magnetic wire itself may be used as a sensing means with a resultant favorable increase in available signal since the lines of flux wrap the magnetic wire many times. Equations concerning the switching performance of a twistor are derived An experimental transistor-driven, 320-bit twistor array has been built. The possibility of applying weaving techniques to future arrays makes the twistor approach appear economically attractive.
TL;DR: In this article, a simple telephone exchange model with an infinite number of trunks and in which traffic depends on two parameters, the calling-rate and the mean holding-time, is considered.
Abstract: This paper considers a simple telephone exchange model which has an infinite number of trunks and in which the traffic depends on two parameters, the calling-rate and the mean holding-time. It is desired to estimate these parameters by observing the model continuously during a finite interval, and noting the calling-time and hang-up time of each call, insofar as these times fall within the interval. It is shown that the resulting information may, for the purpose of this estimate, be reduced without loss to four statistics These statistics are the number of calls found at the start of observation, the number of calls arriving during observation, the number of calls terminated during observation, and the average number of calls existing during the interval of observation. The joint distribution of these sufficient statistics is determined, in principle, by deriving a generating function for it. From this generating function the means, variances, covariances, and correlation coefficients are obtained. Various estimators for the parameters of the model are compared, and some of their distributions, means, and variances presented.
TL;DR: In this article, the regeneration characteristics of self-timing regenerative repeaters are investigated, together with the cumulation of timing deviations in repeater chains and the circuit requirements that must be met to insure satisfactory performance.
Abstract: In self-timing regenerative repeaters, a timing wave for control in pulse regeneration is derived from the binary pulse train at each repeater with the aid of a resonant circuit tuned to the pulse repetition frequency. The timing wave can be made to exercise complete control in retiming of pulses independent of the received pulse train, or it can be combined with the received pulse train to provide partial retiming. The timing principles are discussed here for a particular type of self-timed regenerative repeater invented by Wrathall, in which a timing wave derived from either the received or the regenerated pulse train is combined in a particular way with the received pulse train. The regeneration characteristics of such repeaters as determined by various design parameters are investigated, together with the cumulation of timing deviations in repeater chains and the circuit requirements that must be met to insure satisfactory performance.
TL;DR: In this article, existing data on the environment in which submarine cable systems are placed is summarized and evaluated, and their application to submarine cable system is considered, and the existing data are evaluated and evaluated for the purpose of designing, selecting routes for, placing and repairing this type of communications facility.
Abstract: Information on the environment in which submarine cable systems are placed is of vital interest in designing, selecting routes for, placing, and repairing this type of communications facility. Existing data are summarized and evaluated, and their application to submarine cable systems is considered.
TL;DR: In this paper, a uniform dielectric coat was applied to the inner wall of the waveguide to change the phase constant of the TM 11 wave without affecting appreciably the phase and attenuation constants of the TE 01 wave.
Abstract: The mode conversion from the TE 01 wave to the TM 11 wave which normally occurs in a curved round waveguide may be reduced by applying a uniform dielectric coat a few mils thick to the inner wall of the waveguide. Such a dielectric coat changes the phase constant of the TM 11 wave without affecting appreciably the phase and attenuation constants of the TE 01 wave. Thus, relatively sharp bends can be negotiated to change the direction of the line or deviations from straightness can be tolerated. For each of these two cases a different optimum thickness of the dielectric coat keeps the TE 01 loss at a minimum. At 5.4-mm wavelength a bending radius of 8 ft in a ⅞-inch pipe or 50 ft in a 2-inch pipe can be introduced with 0.2 db mode conversion loss. Deviations from straightness corresponding to an average bending radius of 300 ft can be tolerated in a 2-inch pipe at 5.4-mm wavelength with an increase in TE 01 attenuation of 5 per cent. Serpentine bends caused by equally spaced supports of the pipe may, however, increase the mode conversion and cause appreciable loss at certain discrete frequencies. Compared with the plain waveguide the dielectric-coated guide behaves more critically in such serpentine bends. The mode conversion from TE 01 to the TE 02 , TE 03 , … waves at transitions from a plain waveguide to the dielectric-coated guide is usually very small.
TL;DR: In this article, a comparison of the properties of thin disc samples with those of small spheres is made, and it is shown that discs yield more accurate results in the region below ferromagnetic resonance whereas spheres are preferable for the study of ferrite properties near resonance.
Abstract: Some experimental techniques are discussed which permit measurement of the magnetic and dielectric properties of ferrite materials in the microwave region by observing the perturbation in a cylindrical cavity due to insertion of a small ferrite sample. A comparison of the properties of thin disc samples with those of small spheres shows that discs yield more accurate results in the region below ferromagnetic resonance whereas spheres are preferable for the study of ferrite properties near resonance. A short description of instrumentation for cavity measurements at 9,200 mc is given and experimental results of disc measurements are reported for a low-loss BTL ferrite and several disc diameters. A comparison of experimental results with Polder's theory indicates that the loss of polycrystalline ferrites below resonance is considerably lower than that predicted from an evaluation of the width of the resonance absorption line.
TL;DR: In this paper, the analysis of a type of periodically switched network that might be used in time multiplex systems is performed by successive approximations, based on a block diagram analogous to those used in sampled servomechanisms.
Abstract: This paper concerns itself with the analysis of a type of periodically switched network that might be used in time multiplex systems. The economics of the situation require that the ratio of the switch closure time τ to the switching period T be small. Using this assumption, the analysis is performed by successive approximations. More precisely the zeroth approximation to the transmission is obtained from a block diagram analogous to those used in sampled servomechanisms. From the convergence proof of the successive approximation scheme, it follows that when τ/T is small, the zeroth approximation is very close to the exact transmission. A discussion of some examples is included.
TL;DR: In this article, the number of calls in progress in a simple telephone exchange model characterized by unlimited call capacity, a general probability density of holding-time, and randomly arriving calls is defined as N(t).
Abstract: The number of calls in progress in a simple telephone exchange model characterized by unlimited call capacity, a general probability density of holding-time, and randomly arriving calls is defined as N(t). A formula, due to Riordan, for the generating function of the transition probabilities of N(t) is proved. From this generating function, expressions for the co-variance function of N(t) and for the spectral density of N(t) are determined. It is noted that the distributions of N(t) are completely specified by the co-variance function.
TL;DR: In this paper, a dielectric-coated round waveguide was proposed to remove the degeneracy or equality of phase constants of TE 01 and TM 11 waves in a non-degenerate waveguide, which can be reduced by changing the curvature gradually instead of abruptly.
Abstract: In dielectric-coated round waveguide the degeneracy or equality of phase constants of TE 01 and TM 11 waves is removed. In such a non-degenerate waveguide, mode conversion in bends can be reduced by changing the curvature gradually instead of abruptly. With curvature tapers, which are of the order of, or longer than, the largest beat wavelength between TE 01 and any of the coupled waves, propagation of only one normal mode is maintained throughout the bend. Linear curvature tapers can easily be made by bending the pipe within the limit of elastic deformation. Changes in the direction of a waveguide line can thus be made by inserting a dielectric-coated guide section which is elastically bent over a fixed center point. A thirty degree change of direction of a 2-inch I.D. pipe with 30 ft of a dielectric-coated guide yields a total bend loss at 5.4-mm wavelength that is twice the TE 01 loss in 30 ft of straight pipe. An optimum bend geometry is found which minimizes the total bend loss. The normal mode bend is a broadband device
TL;DR: In this paper, it was shown that the magnitude and temperature dependence of the currents can be explained on the basis of space-charge generated current with a trapping level 0.5 eV below the conduction band or above the valence band.
Abstract: Silicon power rectifiers have been made which have reverse breakdown voltages as high as 2,000 volts and forward characteristics comparable to those obtained in much lower voltage devices. It is shown that the magnitude and temperature dependence of the currents can be explained on the basis of space-charge generated current with a trapping level 0.5 eV below the conduction band or above the valence band. The breakdown voltage of a P+ IN+ diode is computed from avalanche multiplication theory and is shown to be a function of the width of the nearly intrinsic region. A simple diffusion process is evaluated and shown to be adequate for diode fabrication. The characteristics of devices fabricated from high-resistivity compensated, floating-zone refined, and gold-doped silicon are presented. The surface limitation to high inverse voltage rectifiers is discussed.
TL;DR: The Vernier resolver as mentioned in this paper is a precision angle transducer which, from the stand-point of performance, resembles a geared up synchro resolver, except that the step-up ratio between the mechanical angle and the electrical signal is obtained electrically.
Abstract: The Vernier Resolver is a precision angle transducer which, from the stand-point of performance, resembles a geared up synchro resolver, except that the step-up ratio between the mechanical angle and the electrical signal is obtained electrically. Vernier resolvers with step up ratios of 26, 27, 32 and 33 have been designed and built. The unit is a reluctance type, variable coupling transformer. By placing all windings on the stator, sliding contacts are eliminated. Both the stator and the rotor are laminated. Because of the averaging effect inherent in a laminated construction, the accuracy of the unit exceeds by many times the machining accuracy. The performance of present experimental units is characterized by a repeatability of better than ±3 seconds of shaft angle, and a standard deviation error over one full revolution of less than 10 seconds of arc.
TL;DR: In this paper, the effect of birefringence on waveguide propagation was studied in rectangular and circular waveguides with special attention paid to propagation characteristics in guides of arbitrarily small cross-section.
Abstract: A magnetized gyromagnetic medium is birefringent. The effect of birefringence is studied in rectangular and circular waveguides with special attention paid to propagation characteristics in guides of arbitrarily small cross-section. Propagating, small-size structures are found in certain ranges of magnetization for both types of guide.
TL;DR: In this article, an expression for the FM distortion introduced by a transducer whose attenuation and phase shift depend upon the frequency in an arbitrary way was given, which yields useful approximations for the second and third order modulation terms.
Abstract: An expression is given for the FM distortion introduced by a transducer whose attenuation and phase shift depend upon the frequency in an arbitrary way. This expression appears to be difficult to evaluate, but it yields useful approximations for the second and third order modulation terms. In all of the work, it is assumed that the distortion is small compared to the signal, and that the signal can be represented by a random noise having the same power spectrum.
TL;DR: In this paper, the philosophy of repeater and tube design is discussed, and the fundamental reasons for arriving at quite different tube designs are pointed out, some of the tube development problems and the features introduced to eliminate potential difficulties are described.
Abstract: Electron tubes for use in repeatered underwater telephone cable systems must be capable of operating for many years with a reasonable probability of proper functioning. In the new transatlantic telephone cable system the section of the cable between Nova Scotia and Newfoundland contains repeaters developed by the British Post Office Research Station at Dollis Hill. These repeaters are built around the type 6P12 tube developed at that research station. The repeaters contained in the section of the cable system between Newfoundland and Scotland are of Bell System design and depend on the 175HQ tube developed at Bell Telephone Laboratories. In this paper the philosophy of repeater and tube design is discussed, and the fundamental reasons for arriving at quite different tube designs are pointed out. Some of the tube development problems and the features introduced to eliminate potential difficulties are described. Electrical characteristics for the two types are presented and life test data are given. Fabrication and selection problems are outlined and reliability prospects are discussed
TL;DR: In this paper, the performance of submarine telephone cable has been investigated under marine conditions, and a steady rise in capacitance values for GRS-insulated conductors exposed in sea water and sediment under laboratory conditions for thirteen months.
Abstract: The increasing use of submarine telephone cable has resulted in the need for information on the performance of organic materials and cable structures under marine conditions. Recently, Bell Telephone Laboratories initiated a program to acquire fundamental data on the resistance of a wide range of organic materials, as well as immediately applicable engineering information. The present progress report describes the program which includes accelerated, laboratory-microbiological tests, as well as the acquisition of data from actual marine exposures. In biochemical oxygen demand-type tests conducted to date polyethylene was not utilized as a carbon source by marine bacteria. Polyvinyl chloride plastics served as a source of energy for the organisms depending on the way in which the materials were plasticized. Five elastomers were utilized by the bacteria. There has been a steady rise in capacitance values for GRS-insulated conductors exposed in sea water and sediment under laboratory conditions for thirteen months. These increases appear due to biological activity on the insulation. The general performance of materials undergoing marine exposure is reported including reference to penetration of a few synthetic materials by marine borers. Brief mention is made of the examination of submarine cable samples from service.
TL;DR: In this article, the general solution of coupled lines with varying coupling coefficient is applied to a serpentine bend by an iterative process, and evaluated for the elastic curve resulting from a periodically supported line.
Abstract: An otherwise straight waveguide line with equally spaced discrete supports may deform elastically into a serpentine bend under its own weight The TE 01 wave couples in such bends to the TM 11 and TE 1n waves The general solution of coupled lines with varying coupling coefficient is applied to a serpentine bend by an iterative process, and evaluated for the elastic curve resulting from a periodically supported line TE 01 -TM 11 coupling causes only a small increase in TE 01 attenuation Mode conversion to TE 1n waves can become seriously high at certain critical frequencies when the supporting distance is a multiple of the beat wavelength In a copper pipe of 2⅜ inch OD and 2 inch ID, the mode conversion to the TE 12 wave at critical frequencies near 5-mm wavelength causes a TE 01 attenuation increase of 90 per cent and a spurious mode level of −7 db These mode conversion effects can be controlled effectively by inserting mode filters
TL;DR: The first transatlantic telephone one cable system with all its component parts, including the connecting microwave radio-relay system in Nova Scotia, was described in this article, where the authors discuss the technical contribution it has made to the development of world communications.
Abstract: The papers that follow describe the design, manufacture and installalion of the first transatlantic teleph one cable system with all its component parts, including the connecting microwave radio-relay system in Nova Scotia. The purpose of this introd uction is to set the scene in which this project was undert aken, and to discuss the technical contribution it has made to the development of world communications.
TL;DR: In this article, the probability of no coincidences in Poisson patterns has been studied in a variety of practical problems, including reliability of Geiger counters and short-circuits in electric cables.
Abstract: A number of practical problems, including questions about reliability of Geiger counters and short-circuits in electric cables, reduce to the mathematical problem of coincidences in Poisson patterns. This paper presents the probability of no coincidences as well as asymptotic formulas and simple bounds for that probability under a variety of circumstances. The probability of exactly N coincidences is also found in some cases.