Showing papers in "Bell System Technical Journal in 1951"
TL;DR: A new method of estimating the entropy and redundancy of a language is described, which exploits the knowledge of the language statistics possessed by those who speak the language, and depends on experimental results in prediction of the next letter when the preceding text is known.
Abstract: A new method of estimating the entropy and redundancy of a language is described. This method exploits the knowledge of the language statistics possessed by those who speak the language, and depends on experimental results in prediction of the next letter when the preceding text is known. Results of experiments in prediction are given, and some properties of an ideal predictor are developed.
2,556 citations
TL;DR: In this article, the data of E. J. Ryder on the mobility of electrons in electric fields up to 40,000 volts per cm are analyzed and it is estimated that electron “temperatures as high as 4000°K have been produced in specimens having temperatures of atomic vibration of 300° K.
Abstract: The data of E. J. Ryder on the mobility of electrons in electric fields up to 40,000 volts per cm are analyzed. The mobility decreases many fold due to the influence of scattering by optical modes and due to increases of electron energy. It is estimated that electron “temperatures” as high as 4000°K have been produced in specimens having temperatures of atomic vibration of 300° K. The critical drift velocity above which there are deviations from Ohm's law is about 2.6 × 106 cm/sec. This is three times higher than the elementary theory and on explanation in terms of complex energy surfaces is proposed.
416 citations
TL;DR: In this paper, it is argued that imperfect magnetic contact between reproducing head and recording medium may account for much of the high-frequency loss which is experimentally observed, even when the effective spacing is only a few ten-thousandths of an inch.
Abstract: For certain speech studies at the Bell Telephone Laboratories, it has been necessary to design some rather specialized magnetic recording equipment. In connection with this work, it has been found experimentally and theoretically that introducing a spacing of d inches between the reproducing head and the recording medium decreases the reproduced voltage by 54.6 (d/λ) decibels when the recorded wavelength is λ inches. For short wavelengths this loss is many decibels even when the effective spacing is only a few ten-thousandths of an inch. On this basis it is argued that imperfect magnetic contact between reproducing head and recording medium may account for much of the high-frequency loss which is experimentally observed.
290 citations
TL;DR: Transmission by pulse code modulation presents inviting possibilities in the field of television in that information may be relayed by many repeater stations without deterioration.
Abstract: Transmission by pulse code modulation presents inviting possibilities in the field of television in that information may be relayed by many repeater stations without deterioration. In a PCM system, the informal ion signal is periodically sampled and its instantaneous amplitude described by a group of pulses according to a pec-set code. These pulse groups occur at the sampling rate and constitute the transmitted signal. In this process an operation known as amplitude quantization is required.
110 citations
TL;DR: In this paper, the problem of imparting precision and stability to non-metallic resistive materials or of employing metallic ones in new ways is addressed, which is the case with resistors with high values of resistance, of smaller size, and of greater stability over augmented ranges in operating conditions.
Abstract: AN IDEAL resistor would possess a resistance precisely adjusted to value and constant with time, temperature, voltage and frequency under all conditions of use in the application for which it is intended. Wirewound resistors, which early references to “resistance helices” suggest were the first to be employed, approach the ideal in a number of respects. The advent, however, of applications requiring resistors with high values of resistance, of smaller size, and of greater stability over augmented ranges in operating conditions soon made the realization of the ideal more difficult. Moreover, despite great progress in the development of resistance alloys and in the drawing of fine wires from them, the growth of the communications and electronics industries necessitated the development of resistors smaller and cheaper than can be produced from wire and possessing different characteristics. Non-metallic resistive materials were accordingly introduced, even though some of these possess electrical and mechanical properties which are comparatively less stable. The industries now require resistors having the advantages of the non-metallic types and which at the same time are highly precise and stable. The problem, thus, is that of imparting precision and stability to non-metallic resistive materials or of employing metallic ones in new ways.
92 citations
TL;DR: In this paper, the authors compared the adsorption properties of W on W and Ba on W on five different planes and concluded that the extent to which these planes develop depends on T and the applied field, F.
Abstract: The chief conclusions from these studies are given in the Introduction. Table II summarizes the adsorption properties of W on W and Ba on W. These properties vary with the crystal plane and are given for five planes. The extent to which these planes develop depends on T and the applied field, F. The temperature at which W atoms migrate on W at detectable rates depends on the plane and on F, and varies from 800 to 1200°K.
80 citations
TL;DR: In this paper, the authors investigated the properties of the flow fields described by the subject equations with the aim of establishing general properties of flow fields, including the existence or non-existence of classes of exact solutions having certain formal properties.
Abstract: The subject equations are investigated with the aim of establishing some general properties of the flow fields which they describe, including the existence or non-existence of classes of exact solutions having certain formal properties. The results include a number of geometric characteristics of the vector fields involved, a suggestive reformulation of the partial differential equations restricting carrier concentration and electrostatic potential, and several classes of exact solutions involving arbitrary constants and/or functions. Of particular interest is a family of solutions in closed form for the steady-state, no-recombination case involving an arbitrary harmonic function in three dimensions.
72 citations
TL;DR: In this paper, a relatively new approach to the solution of negative impedance problems related to vacuum tube circuits is presented, which consists of reducing the vacuum tube circuit of a device for producing negative impedance to an electrically equivalent four-terminal network from which the stability and the operation of the device as an element in a system can be predicted accurately.
Abstract: This paper presents a relatively new approach to the solution of negative impedance problems related to vacuum tube circuits. The approach consists of reducing the vacuum tube circuit of a device for producing negative impedance to an electrically equivalent four-terminal network from which the stability and the operation of the device as an element in a system can be predicted accurately. The theory is of interest at this time because a negative impedance repeater, the E1, has recently been developed for use in the exchange plant. It has been found that such a repeater can be placed in series with a voice frequency telephone line to provide transmission gains which are ample for many purposes.
69 citations
TL;DR: In this paper, the propagation constant of the wave is obtained in terms of the properties of the electron stream and the impedance of the circuit, and the importance of fitting boundary conditions in the solution of an actual problem is discussed.
Abstract: This paper reviews some of the assumptions made and some of the general problems involved in analyzing the behavior of electron streams coupled to circuits. It explains why a wave approach is used. The propagation constant of the wave is obtained in terms of the properties of the electron stream and the impedance of the circuit. Some general properties of waves are discussed. The importance of fitting boundary conditions in the solution of an actual problem is discussed, and examples, including that of “backward-gaining” waves, are discussed.
52 citations
TL;DR: In this paper, the general properties of the longitudinal modes in cylinders and slabs are investigated with the aid of the close formal analogy between the dispersion equations for the two cases.
Abstract: The general properties of the longitudinal modes in cylinders and slabs are developed with the aid of the close formal analogy between the dispersion equations for the two cases.
50 citations
TL;DR: In this paper, the elastic constants of nickel crystals and their variation with magnetic field (ΔE effect) have been measured by a 10-megacycle ultrasonic pulsing method, and it was shown that the small effect observed at 10 megacycles is due to a relaxation in the domain wall motion due to microeddy-current damping.
Abstract: The elastic constants of nickel crystals, and their variation with magnetic field (ΔE effect), have been measured by a 10-megacycle ultrasonic pulsing method. The constants of three crystals agree well with one another when the crystals are magnetically saturated, but vary with domain distribution when demagnetized. The maximum ΔE effect observed is much less (3%) than has been observed at lower frequencies (20%). By measuring the ΔE effect and the decrement of polycrystalline rods at low frequencies, it is shown that the small effect observed at 10 megacycles is due to a relaxation in the domain wall motion due to microeddy-current damping. From the initial slope of the decrement-frequency curve, and also from the frequency of maximum decrement, the size of the average domain is found to he about 0.04 mm. Actual domains in single nickel crystals have been observed optically by Williams, who finds domain widths of 0.02 to 0.2 mm.
TL;DR: The TD-2 microwave radio relay system is a recent addition to the telephone plant facilities for long distance communication as discussed by the authors, which is designed to supplement the coaxial system and to provide greatly expanded facilities for nationwide transmission of broad-band signals such as television pictures or large groups of message circuits.
Abstract: The TD-2 microwave radio relay system is a recent addition to the telephone plant facilities for long distance communication. It is designed to supplement the coaxial system and to provide greatly expanded facilities for nationwide transmission of broad-band signals such as television pictures or large groups of message circuits. The system makes use of many microwave repeaters located 25 to 30 miles apart in line-of-sight steps. The great variety and number of components which make up such a system require the engineering of all components to close tolerances. This paper describes the system in some detail from the standpoints of overall objectives, component designs to meet such objectives and facilities for the maintenance of overall performance.
TL;DR: In this paper, the first four semi-invariants of the distribution of the average of traffic carried by a telephone system with an infinite number of trunks, during a period of statistical equilibrium were determined.
Abstract: This paper describes the determination of the first four semi-invariants of the distribution of the average, over an arbitrary time interval, of traffic carried by a telephone system with an infinite number of trunks, during a period of statistical equilibrium Both finite and infinite numbers of independent call sources are considered, and the distribution function of call holding times is left general
TL;DR: In this article, a general method for designing networks with assigned gain or phase characteristics is developed based on the analogy between the gain and phase of linear networks and two-dimensional potential and stream functions, produced by charges corresponding to the network singularities.
Abstract: A general method is developed for designing networks with assigned gain or phase characteristics. It is based on the analogy between the gain and phase of linear networks and two-dimensional potential and stream functions, produced by charges corresponding to the network singularities. These analogies exist because the gain and phase functions are the real and imaginary parts of analytic functions of a complex frequency variable. Potential theory is used here to determine charge arrays which correspond to physical network singularities and also yield approximations to assigned potential or stream functions.
TL;DR: In this paper, the authors considered the problem of terminating a transmission line completely filled with laminated material and gave an analysis of the modes of transmission in a laminated line, and of the problems of terminating such a line.
Abstract: It has recently been discovered that it is possible to reduce skin effect losses in transmission lines by properly laminating the conductors and adjusting the velocity of transmission of the waves. The theory for such laminated transmission lines is presented in the case of planar systems for both infinitesimally thin laminae and laminae of finite thickness. A transmission line completely filled with laminated material is discussed. An analysis is given of the modes of transmission in a laminated line, and of the problem of terminating such a line.
TL;DR: In this article, the performance of a few early experimental units of a new kind of transistor has been analyzed and shown to be a stable, high gain, and quiet amplifier of considerable practical interest.
Abstract: Shockley, Sparks, and Teal have recently described the physical properties of a new kind of transistor. Preliminary studies of circuit performance show that it is a stable, high gain, quiet amplifier of considerable practical interest. This paper analyzes the performance of a few early experimental units.
TL;DR: In this article, contrast and resolution in electron micrographs from thin replica films are determined by the geometrical relationships between the directions of incidence of the condensing atom beam and the local surface normal, during film formation by evaporation in vacuo, and the direction of the electron beam, during subsequent exposure in the microscope.
Abstract: Contrast and resolution in electron micrographs from thin replica films are determined by the geometrical relationships between the directions of incidence of the condensing atom beam and the local surface normal, during film formation by evaporation in vacuo, and the direction of incidence of the electron beam, during subsequent exposure in the microscope. Replica films may be formed of any material suitable for vacuum evaporation. Metal atoms in general lend to stick where they strike, moving only short distances, 100 A or less, to nucleating centers where they form small crystallites. Oxides such as silica and silicon monoxide, and also the semi-metal germanium, form amorphous films. A portion of the incident material, about 50% in the case of silica, migrates large distances, 5000 A or more, before finally condensing; the remainder sticks where it first strikes the surface. The existence of a minimum perceptible mass thickness difference, about 0.7 μUg/cm2 for 50 kv electrons, results in an optimum replica mass thickness of about 10 μg/cm2. The resolution of the replica film is proportional to its linear thickness and hence is inversely proportional to its density. Micrographs of silica, chromium, gold-manganin, aluminum, aluminum-platinum-chromium and germanium replicas are shown. The importance of stereoscopic methods in interpretation of micrographs is discussed.
TL;DR: In this article, it was shown that the type of image obtained depends upon the local bending of the crystal, the coherent crystal size and the state of internal strain, and the absence of extinction contours seen in annealed aluminum is an indication of the presence of internal strains.
Abstract: Features of the dynamical or wave mechanical theory of electron diffraction pertinent to the interpretation of electron images of crystalline materials are briefly discussed. It is shown that the type of image obtained depends upon the local bending of the crystal, the coherent crystal size and the state of internal strain. The absence of extinction contours seen in annealed aluminum is an indication of the presence of internal strains.
TL;DR: In this article, the elastic constants of low temperature coefficient crystals have been evaluated in the temperature range from −100°C to +200°C, and it is shown that there is a maximum temperature of 190°C for which an AT type crystal can have a zero temperature coefficient.
Abstract: In order to determine the angles of cuts for low temperature coefficient crystals, the elastic constants of quartz have been evaluated in the temperature range from −100°C to +200°C. This has been done by measuring a series of rotated Y-cut crystals in the thickness shear mode and a series of rotated X-cuts in the longitudinal length mode. From the measurements, low temperature coefficients AT, BT, CT, and DT type crystals can be determined which have their temperature of zero temperature coefficient at any prescribed temperature. Calculations are given for the properties of crystals to operate at 200°C. The characteristics of an AT type crystal have been investigated experimentally, and the measured results are in reasonable agreement with the calculations. It is shown that there is a maximum temperature of 190°C for which an AT type crystal can have a zero temperature coefficient.
TL;DR: The N1 Carrier System as mentioned in this paper is a 12-channel double-sideband system for single cable application with low loss, stable, high velocity service for toll and exchange circuits in the range from 15 or 20 miles to 200 miles.
Abstract: The N1 Carrier System is a 12-channel, double-sideband system for single cable application. It provides low loss, stable, high velocity service for toll and exchange circuits in the range from 15 or 20 miles to 200 miles. Units and sub-assemblies are miniaturized and arranged on a plug-in basis. Emphasis has been placed on reduction in cost of components, as well as simplification of manufacturing methods, engineering, installation and maintenance. Economy is achieved by many novel features, principal among which is a built-in low cost compandor. By compressing and expanding the volume range of speech, the compandor permits much higher tolerance of noise and crosstalk, thereby substantially lowering the cost of both line and terminal facilities. Other important features are self contained dialing and supervisory signaling, an individual channel regulator, and automatic equalization through the use of “frequency frogging,” or interchange of high- and low-frequency groups at each repeater.
TL;DR: In this paper, a simple electron gun consisting of a cathode and two apertured planes held at different potentials is used as electron lenses, and when the gun is immersed in a uniform axial magnetic field the aperture spacings and potentials can be chosen so that the emerging electrons have no radial velocities.
Abstract: In a simple electron gun consisting of a cathode and two apertured planes held at different potentials the apertures act as electron lenses. When the gun is immersed in a uniform axial magnetic field the aperture spacings and potentials can be chosen so that the emerging electrons have no radial velocities.
TL;DR: The familiar telephone set has undergone numerous changes which will provide better service at lower cost than do present models.
Abstract: A new common battery telephone set has been developed and is now in production which is materially better than previous types in performance and convenience to the user. This paper describes this set, and discusses, as typical of Bell System dleveopment processes, the contributions of the operating, development, and manufacturing organizations to the final design. It also describes the evaluation of the design by the controlled service trial, in terms of the results produced in actual service in the hands of the public.
TL;DR: In this article, the reflection coefficient is computed as a function of the energy of the incident electrons, over the range from 0 to 20 electron volts, for a variety of values of the parameters which define the model of the crystal.
Abstract: This paper gives the results of some calculations of the reflection coefficient for electrons incident normally on a plane face of a metallic crystal. The physical situation is treated as being one-dimensional; and it is assumed that the potential energy of an electron is a sinusoidal function of distance inside the crystal, and obeys the classical image force law outside the crystal. The reflection coefficient is computed as a function of the energy of the incident electrons, over the range from 0 to 20 electron volts, for a variety of values of the parameters which define the model of the crystal.
TL;DR: In this paper, the relationship between the properties of a vacuum tube triode and those of a transistor is discussed and a number of examples of transistors being used to transform a known vacuum tube circuit into one suitable for use with transistors.
Abstract: Because of a relationship which exists between the properties of a vacuum tube triode and those of a transistor, it is possible to start with a known vacuum tube circuit and to transform it into a completely different circuit suitable for use with transistors. The nature of this transformation is discussed and a number of examples are given.
TL;DR: In this paper, a photographic method using mechanical scanning for displaying the space patterns of sound and microwaves is described, where a probe pick-up scans the sound or microwave field and the amplified probe output controls the brilliance of a small lamp affixed to the probe.
Abstract: A photographic method using mechanical scanning for displaying the space patterns of sound and microwaves is described. A probe pick-up scans the sound or microwave field and the amplified probe output controls the brilliance of a small lamp affixed to the probe. A camera set at time exposure records the light intensity variations of the lamp as it moves across the scanned field, forming a pattern on the film of the amplitude distribution. Phase fronts can be delineated by adding a constant amplitude signal to the probe output. Photographs are included which show: sound and microwave patterns of lenses, diffraction at a straight edge and disk, refraction by a prism, diffusion of sound by a divergent lens, and radiation from loud speakers. Also, by transposition of source and receiver, directional patterns of transducers acting as microphones are obtained which (by reciprocity) appear identical with their radiation patterns. This provides a means for examining the directional characteristics of non-reversible transducers such as a carbon microphone. A calibration method is described which allows the relative value of the field intensities to be determined.
TL;DR: In this paper, a new type of telephone receiver is described, in which the permanent magnet, the pole piece and the armature, which drives a light weight dome, are all ring-shaped parts.
Abstract: A new type of telephone receiver is described, in which the permanent magnet, the pole piece and the armature, which drives a light weight dome, are all ring-shaped parts. This structure exhibits a substantially higher grade of performance than present receivers of the bipolar type, with regard to efficiency, frequency range, leakage noise level, and response when held off the ear. In addition to showing the characteristics of this new receiver, an analysis of the various losses is given, and ideal performance limits are established. The advantage of providing an auxiliary path for the air gap flux is indicated, and other applications of the device as a transducer are described.
TL;DR: In this paper, a general solution of the electron stream equations for a parallel plane diode, under the assumption that the electron velocity is single valued, was developed, which serves to unify the wave theory and the particle theory of electron flow and is an approximation for multi-velocity streams over a wide range of conditions.
Abstract: A general solution of the electron stream equations is developed for a parallel plane diode, under the assumption that the electron velocity is single valued. This solution contains all particular solutions. It serves to unify the wave theory and the particle theory of electron flow, and it is an approximation for multi-velocity streams over a wide range of conditions.
Journal Article•
TL;DR: In this paper, the authors discuss the theory of the instantaneous compandor and evaluate the noise advantage when instantaneous companding is applied to telephone channels, depending upon the noise standard of the system.
Abstract: Instantaneous compandors have found useful application in time-division systems. This paper discusses the theory of the instantaneous compandor and evaluates the noise advantage when instantaneous companding is applied to telephone channels. The noise advantage depends upon the noise standard of the system. If the standard corresponds to that of a toll telephone system, a noise advantage of about 20 db is possible.
TL;DR: In this paper, the synthesis of any N-terminal switching function is accomplished using a gang of selector switches, and the synthesis method is proved to be economical in the sense that the switching functions which can be synthesized by any other method using much fewer contacts comprise a vanishingly small fraction of the total of all possible switching functions.
Abstract: The circuits considered have N accessible terminals and are operated by gangs of selector switches. Synthesis of any N-terminal switching function is accomplished. The synthesis method is proved to be economical in the sense that the switching functions which can be synthesized by any other method using much fewer contacts comprise a vanishingly small fraction of the total of all possible switching functions.
TL;DR: The first sentence to be transmitted by telephone was transmitted by Alexander Graham Bell on March 10, 1876 as mentioned in this paper, where the inventor spoke and his assistant heard the first sentence: “MR. WATSON, COME HERE; I WANT YOU.
Abstract: SEVENTY-FIVE years ago — on March 10, 1876 — the inventor spoke and his assistant heard the first sentence to be transmitted by telephone: “MR. WATSON, COME HERE; I WANT YOU.” Three days earlier, U.S. Patent No. 174,465 had been granted to Alexander Graham Bell for his concept of means for making the conversion between the air vibrations of an uttered sound and their corresponding electrical undulations.