Showing papers in "Bell System Technical Journal in 1944"
TL;DR: In this paper, the authors used the representations of the noise currents given in Section 2.8 to derive some statistical properties of I(t) and its zeros and maxima.
Abstract: In this section we use the representations of the noise currents given in section 2.8 to derive some statistical properties of I(t). The first six sections are concerned with the probability distribution of I(t) and of its zeros and maxima. Sections 3.7 and 3.8 are concerned with the statistical properties of the envelope of I(t). Fluctuations of integrals involving I2(t) are discussed in section 3.9. The probability distribution of a sine wave plus a noise current is given in 3.10 and in 3.11 an alternative method of deriving the results of Part III is mentioned. Prof. Uhlenbeck has pointed out that much of the material in this Part is closely connected with the theory of Markoff processes. Also S. Chandrasekhar has written a review of a class of physical problems which is related, in a general way, to the present subject.22
5,806 citations
TL;DR: In this paper, it was shown that changes in band width are detectable about twice as readily with music as with speech, and that one must go from 8 to 15 kc to obtain a change as readily detected as a change from 5 to 8 kc; and that both these changes, for speech, are just sufficient to have an even chance of being detected by listeners having experience in such tests.
Abstract: One of the factors that should be considered in determining how wide a transmission band is required for high fidelity broadcasting is the ability of people to perceive the effects of restricting the band to various limits, when listening to typical radio programs. Tests are described in which this was directly measured. The tests were concerned only with the physical ability to hear the differences in band width and disregarded the question of the enjoyment or aesthetic appreciation of wider bands. It is concluded that changes in band width are detectable about twice as readily with music as with speech; that one must go from 8 to 15 kc. to obtain a change as readily detected as a change from 5 to 8 kc.; and that both these changes, for speech, are just sufficient to have an even chance of being detected by listeners having experience in such tests.
33 citations
TL;DR: In this article, a comprehensive view of the various types of crystal cuts is presented, as well as some of the methods employed in choosing the proper cut for a given requirement, the manner in which quartz crystals vibrate and the basic principles governing the choice of a design to use certain cuts most advantageously.
Abstract: WITH the recent extended use of Quartz crystals in oscillators and electrical networks has come a need for a comprehensive view of the various types of crystal cuts. In addition there has been a need for illustration of some of the methods employed in choosing the proper cut for a given requirement, the manner in which quartz crystals vibrate and the basic principles governing the choice of a design to use certain cuts most advantageously. In particular one of the greatest problems associated with the recent large scale production of crystals for oscillator purposes has been that of obtaining crystals the activity and frequency of which would not vary to any large degree over a wide range in temperature.
32 citations
TL;DR: In this paper, the resonant frequencies associated with the three general modes of motion (i.e., extensional, shear, and flexural) were analyzed in some detail, and the formulation of the general problem along classical lines was developed.
Abstract: The comparatively recent advent of crystal controlled oscillators and of wave filters employing piezoelectric elements has resulted in an extensive study of the ways in which plates made of elastic materials such as quartz or rochelle salt can vibrate. Of special interest have been the resonant frequencies associated with these modes of motion. As will be indicated in subsequent paragraphs, the general solution to the problem of greatest interest is quite complex, and has not been forthcoming, (i.e., as applied to rectangular plates completely unrestrained at all boundary surfaces). For this reason numerous approximate solutions have been developed which yield useful information in spite of their limitations. Several of these solutions will be discussed in the following sections. The three general types of modes (i.e., the extensional, shear, and flexural) will be analyzed in some detail. Also, as a preliminary step the formulation of the general problem along classical lines will be developed.
15 citations
TL;DR: From some results of a simpler nature, which do not require a consideration of the distribution of the signal and noise energies as functions of frequency, are derived the solution of the general problem.
Abstract: When the input to a rectifier contains both signal and noise components, the resultant output is a complicated non-linear function of signal and noise. Given the spectra of the signal and noise input waves, the law of rectification, and the transmission characteristics of the input and output circuits of the rectifier, it should, in general, be possible to describe the spectrum of the resultant output wave. Before discussing the solution of the general problem, we shall derive some results of a simpler nature, which do not require a consideration of the distribution of the signal and noise energies as functions of frequency.
10 citations
TL;DR: In this article, a method of analyzing telephone receiver characteristics by indicial response is discussed and illustrated by oscillograms, which is the instantaneous response of the receiver to a suddenly applied electromotive force.
Abstract: A method of analyzing telephone receiver characteristics by indicial response is discussed and illustrated by oscillograms. The indicial response of a telephone receiver is the instantaneous response of the receiver to a suddenly applied electromotive force. This type of response is of particular fundamental interest because it furnishes a key to the solution of transient problems such as are involved in the response to speech waves.
5 citations
TL;DR: In this paper, the theory underlying the measurement of dielectric constants and power Iactors by means of resonant lengths of coaxial transmission line is developed, apparatus used for such measurements is illustrated and the measurement routine described.
Abstract: The theory underlying the measurement of dielectric constants and power Iactors, by means of resonant lengths of coaxial transmission line, is developed, apparatus used for such measurements is illustrated and the measurement routine described. A table of typical results is appended together withan “X tan X” table for aid in the calculations.
5 citations
TL;DR: A historical review appearing for various reasons to be the most suitable to commemorate the retirement of Dr. F. B. Jewett is found.
Abstract: SOME few months ago, in anticipation of the retirement of Dr. F. B. Jewett, an informal committee undertook to discover such action as the Journal might appropriately take to commemorate the event. The various possibilities finally narrowed down to one, a historical review appearing for various reasons to be the most suitable.
4 citations
TL;DR: In this article, a series of papers dealing with piezoelectric circuit elements and their manufacture is presented, with a focus on the manufacturing process and the components of the circuit.1 Certain parts of the paper are not new or original but have been added for the sake of completeness and for the convenience of the reader.
Abstract: This paper is one of a series of papers dealing with piezoelectric circuit elements and their manufacture.1 Certain parts of the paper are not new or original, but have been added for the sake of completeness and for the convenience of the reader.
4 citations
TL;DR: In this paper, a series of articles on piezoelectric quartz plates is presented, focusing mainly on the methods employed in mounting crystal plates operating up to approximately one megacycle for practical utilization in communication equipment.
Abstract: THIS paper is one of a series on piezoelectric quartz plates and deals primarily with the methods employed in mounting crystal plates operating up to approximately one megacycle for practical utilization in communication equipment. The theoretical aspects of mounting crystals have been covered in Chapter VII. The discussion is confined to plates1 having definite nodal lines or points, such as +5° and −18° 25′ X cuts, GT, CT, DT, MT and NT cuts. The mounting of high-frequency crystal plates such as AT and BT cuts, which vibrate in thickness shear modes, is not included. It should also be noted that the subject matter is treated descriptively and that no attempt is made to go into the more intricate details of design or to give performance characteristics. These matters will be dealt with fully in a later paper. The designs and methods outlined are up to date for each type of unit, the results of many years of development on the part of Bell System engineers to evolve practical designs for commercial manufacture and use. Expanding on the contributions of the early investigators mentioned by W. P. Mason in Chapter I,1 these engineers had, in the ten years prior to 1939, worked out practical designs and developed suitable tools and processes for wide commercialization in telephone applications. In the last five years, under the impetus of war, further improvements have been made in the design and manufacture of crystal units, particularly those for use by the Armed Forces.
4 citations
TL;DR: In this paper, a new type of vacuum tube is described in which a flat radial beam of electrons in a cylindrical structure may be made to rotate about the axis, and the focusing of the beams and their directional control are accomplished by the magnetic fields in small polyphase motor stators.
Abstract: A new type of vacuum tube is described in which a flat radial beam of electrons in a cylindrical structure may be made to rotate about the axis. Features of the tube are its absence of an internal focusing structure and resultant simplicity of design, its small size, its low voltages, and its high beam currents. The focusing of the beams and their directional control are accomplished by the magnetic fields in small polyphase motor stators. A time division multiplex signaling system for 30 channels using these tubes is briefly described.
TL;DR: In this article, the causes of distortion occurring both externally and internally to the receiver and the effects of such distortion on the operating margins are described and some of the more important considerations involved in establishing distortion tolerance criteria are discussed.
Abstract: Recent practical and theoretical investigations of the effect of signal distortion on the margins of operation of start-stop telegraph receivers have led to the development of improved methods of testing and adjusting receivers, have enabled criteria of distortion tolerance to be set up for subscribers' and monitoring receivers and regenerative repeaters, and have made possible the application of more convenient and accurate standards of telegraph transmission. This paper describes the causes of distortion occurring both externally and internally to the receiver and the effects of such distortion on the operating margins. Methods of determining the internal distortion of a receiver are described and some of the more important considerations involved in establishing distortion tolerance criteria are discussed.
TL;DR: The first telephone use of crystal units in the commercial manufacture of filters was made by the Western Electric Company in about 1936 as discussed by the authors, and the quantitative data collected for this purpose provided the chief source of material for this chapter.
Abstract: THIS chapter emphasizes primarily the need for close control in the manufacture of crystal units for use in filters. The first telephone use of crystal units in the commercial manufacture of filters was made by the Western Electric Company in about 1936. To make such commercial manufacture practical, it was necessary to establish accurate design information and allowable manufacturing tolerances. The quantitative data collected for this purpose provided the chief source of material for this chapter. While the data is quite extensive, it will be observed that there are still some factors which must be treated qualitatively.
TL;DR: In this paper, the fundamental considerations involved that govern the design of mountings or holders of quartz crystals are discussed, restricted to the three common types, namely, rod or clamp type, wire type and airgap type.
Abstract: IT IS the object of this chapter to show some of the fundamental considerations involved that govern the design of mountings or holders of quartz crystals. This discussion is restricted to the three common types, namely, rod or clamp type, wire type and airgap type. The development of these three types of mountings for applications in telephone transmission and radio systems has led to many and varied forms. Commercial designs of units for telephone uses employing these principles are described in detail in a later chapter.
TL;DR: In this paper, a correlated review of the powder metallurgy process is presented in order to acquaint telephone engineers with an increasingly important production method, and to provide an outline of topic references that could otherwise be obtained only from many different sources.
Abstract: THIS correlated review is an attempt to present some of the more common aspects of the powder metallurgy process in order to acquaint telephone engineers with an increasingly important production method, and to provide an outline of topic references that could otherwise be obtained only from many different sources.