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Proceedings of the IEE - Part B: Radio and Electronic Engineering

Issue 26 • Date March 1959

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Displaying Results 1 - 25 of 26
  • Rating of speech links and performance of telephone networks

    Page(s): 65 - 76
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1951 KB)  

    A serious problem which occurs in the development of large or otherwise costly speech communication systems (the term includes, but is not confined to, public telephone systems) is the achievement of a consistent overall design that is economical and yet never requires users to exert unreasonable amounts of mental or vocal effort in conversation. The ideal thus simply expressed is notoriously difficult to achieve and the problem is of long standing in the history of telephony. The paper reconsiders this problem and sets out a coherent `design¿ procedure by which studies of rating (providing figures of merit in terms that are meaningful for engineering design purposes) and user evaluation (study of merits of speech links for particular applications) can be conducted to yield closely complementary information. These two aspects, `rating¿ and `user evaluation¿, are concerned respectively with individual speech links and with systems or networks viewed as aggregates of such links. A further type of study, also important, deals with estimating the grade of performance which a complete network, designed to a given transmission plan, will provide; this can be described in statistical terms such as the proportion of calls of various types whose transmission should yield various levels of satisfactoriness to users. This last type of study, conveniently known as `network transmission performance¿, is of special value in the long-term planning and operation of large systems. View full abstract»

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  • Assessment of speech communication links

    Page(s): 77 - 89
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2168 KB)  

    Testing methods, such as `articulation¿, `immediate appreciation¿, etc., at present available for providing a direct measure of the performance or effectiveness of a link for speech communication are not individually or even collectively applicable over any wide ranges of levels of performance or types of link. Many practical links fall outside the range over which these methods are reliable, and there is need for a general method that will both provide a safeguard against unrealistic results and serve, if possible, to extend the usefulness of existing techniques. The paper examines the mechanism of conversation over a speech link and deduces a sequence of criteria each applicable over an appropriate range of performance. A general assessment method follows from this, and the corresponding experimental techniques (which depend on the use of ordinary untrained subjects) and some applications are discussed. Some existing assessment methods can be fitted into the framework provided by the general method and can then be used with increased confidence. Assessments as described in the paper are of little value for indicating the merit a link has for the user. Their most valuable use is to facilitate (as part of the process known as rating) realistic comparisons of links with Standard Speech Links whose evaluation can be studied in actual use. View full abstract»

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  • The use of dispersive artificial dielectrics in a beam-scanning prism

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1170 KB)  

    The direction of a radiated beam can be altered by passing it through a prism. If the prism material is dispersive, the final direction is frequency sensitive and beam scanning can therefore be achieved by frequency modulation. Two types of dispersive artificial dielectric are considered for use in such a prism, one consisting of an array of rods, and the other of an array of sheets containing a pattern of resonant slots. Measured values of the electrical constants of both arrays over a wide range of wavelengths are included, and the properties of the beam-scanning prism are described in detail. View full abstract»

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  • The quarter-wave matching of dispersive materials

    Page(s): 103 - 106
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (351 KB)  

    Reflections from the surfaces of dispersive materials used in broadband aerial systems are highly frequency-dependent. A technique for matching such materials is described, and results are included of a successful application to the input surface of a dispersive prism. View full abstract»

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  • Theory of reflections from the rodded-type artificial dielectric

    Page(s): 107 - 114
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    It is demonstrated that a composite material of a solid dielectric with embedded conductors can give a wave impedance equivalent to that of free space, and thus eliminate interface reflections. A particular material, the rodded dielectric, is analysed, and design procedures are given which are exemplified by numerical results. An experimental verification of the design theory when the electric-field vector is wholly parallel to the axes of the rods is described, and the results show good agreement with the theory. Finally, methods of manufacture, and the tolerances required, are discussed. View full abstract»

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  • An investigation of the excitation of radiation by surface waves

    Page(s): 116 - 122
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (814 KB)  

    The graphical method of measuring a reflection coefficient through a junction, originated by Deschamps, is used to determine the transmission efficiency of a surface wave at a discontinuity. The radiations excited by the surface wave at a discontinuity in surface reactance, and at an edge of a metallic strip above a reactive surface, are investigated. It is shown that the discontinuities cause the radiation of an appreciable fraction of the incident power. A matching step at the discontinuity in surface reactance is found to have no effect on the excitation of radiation. Further, it is found that, compared with the radiation excited at the edge of a metallic strip, the radiation excited at a discontinuity in surface reactance is confined to a narrower angle above the surface. View full abstract»

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  • The launching of radial cylindrical surface waves by a circumferential slot

    Page(s): 123 - 128
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (633 KB)  

    The efficiency with which radial cylindrical surface waves may be launched by a circumferential slot is investigated theoretically and experimentally. The radius of the slot has been found to affect the launching efficiency very little. An optimum efficiency of about 68% is obtainable with a slot of 2cm radius above a 58-ohm reactive surface. View full abstract»

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  • Parallel-plate transmission systems for microwave frequencies

    Page(s): 129 - 140
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1566 KB)  

    The paper gives a practical account of parallel-plate, or strip, transmission lines, which are becoming of increasing importance in microwave applications. The different types of strip line are considered and their basic characteristics summarized. Transducers to conventional systems and various circuit-elements are described, while the application of strip-line techniques to the construction of microwave components and filters is examined. Manufacture by photo-etching is outlined. View full abstract»

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  • Optical techniques at microwave frequencies

    Page(s): 141 - 157
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2410 KB)  

    The paper reviews the application of optical principles and techniques at microwave frequencies. A brief discussion of radiation and diffraction in the far and near fields is first given. This is followed by an account of the various types of artificial dielectric. Methods for reducing and enhancing surface reflectivity are examined, and several instruments and components, which are especially useful at millimetre wavelengths, are considered. The survey concludes with a bibliography. View full abstract»

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  • A new method of generating a rotating radiation polar diagram

    Page(s): 158 - 169
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1566 KB)  

    In recent years, there has been a tendency to introduce new navigational aids which utilize rotating aerial arrays of large electrical dimensions in order to obtain highly accurate navigational information; one such example is the well-known system called Tacan. In general, the rotation of large arrays introduces severe mechanical problems which fix a lower limit of about 300 Mc/s to the operating radio frequencies of these aids. For many purposes it is desirable to operate in the 100 Mc/s region, and the paper describes a method by which this object may be achieved. Briefly, it consists of rotating an aerial array of small mechanical dimensions and allowing it to be coupled electrically to a static array of very large dimensions which acts as the final radiator of electromagnetic energy. The efficiency of coupling and the form of the static array are such as to produce a final radiation which makes the rotatable array appear to have the large dimensions of the static array. In effect, the method is similar to the familiar `goniometer¿ technique. The method is described with reference to its application in a new and more accurate form of Vor system (v.h.f. omni-range) known as Vorac. The paper also describes how the new method itself helps to improve the vertical elevational performance of a conventional Vor system. View full abstract»

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  • Transistor active filters using twin-T rejection networks

    Page(s): 170 - 174
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (442 KB)  

    The introduction of a rejection-type network, such as a twin-T or a bridged-T, into the feedback loop of an amplifier leads to bandpass characteristics similar to those of single tuned circuits. It is possible to achieve highly selective circuits at very low frequencies, e.g. in the audio range, where high-Q-factor coils are usually physically large and expensive. Some basic circuits using a symmetrical twin-T network with R and C only in the feedback loop of a transistor amplifier are investigated. Results of measurements are given. Q-factors higher than 50 are obtained at a frequency of 600 c/s. View full abstract»

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  • The transformation of admittance through a matching section and lossless waveguide junction

    Page(s): 175 - 179
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (567 KB)  

    The paper describes a method of setting up a matching section, comprising a variable reactor and phase shifter, in cascade with a lossless waveguide junction to obtain a particular admittance transformation. The terminal planes are defined by the position of voltage zeros when the junction is terminated by a short-circuit. The matching section and junction are regarded as two junctions in cascade and, using conventional theory, the relation between the admittance transformation parameters and input-voltage reflection coefficients is derived. Some experimental results obtained using an S-band waveguide system are quoted to demonstrate the application of the theory. View full abstract»

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  • The power radiated by a surface wave circulating around a cylindrical surface

    Page(s): 180 - 185
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (681 KB)  

    Recognizing the evanescent character of the surface-wave field distribution over the equi-phase planes and the important part played by the inclination of these planes with the normal to the interface when power is transferred across it, calculations are made for radiation arising when a wave of this kind circulates around a highly reactive supporting surface of cylindrical form. It is concluded that, when the surface has a finite loss, there will be a particular radius of curvature for which the surface wave progresses for a limited distance without attenuation. View full abstract»

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  • The recognition of moving vehicles by electronic means

    Page(s): 186 - 195
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1311 KB)  

    The increasing congestion of traffic in London's streets has been a matter of major concern to London Transport for many years, and the maintenance of service regularity in these difficult circumstances has so far been achieved with some degree of success by additional supervision of operating personnel. The paper describes a method whereby, without any additions to the road staff, an increasing amount of information can be given at a central control point as to the movement of buses. This should enable measures to be taken before conditions deteriorate, and thus minimize service irregularities. Details of an equipment which has been developed for this purpose are given, and the component items of the equipment, namely the identification markings on each bus, the roadside scanning and sending units and the central receiving and presentation cabinet, are described. A later Section of the paper forecasts improvements and developments which are visualized for the future, and although this equipment has been designed to deal with a specific bus operating problem, it should have numerous applications wherever a number of moving objects need to be recorded. View full abstract»

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  • Pattern recognition by means of automatic analogue apparatus

    Page(s): 198 - 209
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1784 KB)  

    The problem of synthesizing apparatus that will automatically simulate man's ability to recognize and to learn to recognize patterns is discussed and it is concluded that analogue circuits, rather than the digital switching circuits that have been employed in the past, provide the simpler solution. A new circuit unit that possesses many of the essential functional characteristics exhibited by nerve cells in the brain is derived from earlier work on the electrical simulation of nervous-system functional activity and forms the basic element of the circuits. The new analogue apparatus consists of a number of distinct functional circuits arranged in a definite sequence, through which signals derived from the patterns to be recognized pass simultaneously on their way to the final output terminals. Classification information may be built into the apparatus initially if it is available, but if not, it can be stored automatically in a special unit during a setting-up procedure in which samples of the pattern types that the apparatus will be required to recognize are presented, together with identification signals. Low-resolution automatic pattern-recognition apparatus is described, and examples illustrate the setting-up procedure and subsequent performance of the apparatus. View full abstract»

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  • A system for the automatic recognition of patterns

    Page(s): 210 - 221
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1540 KB)  

    The paper describes a new method for the automatic recognition of patterns. The method may be applied to any form of spatial pattern, but in the present instance, patterns consisting of line figures are considered. The pattern is presented to a flying-spot scanner connected to a digital computer. The shape of the pattern is analysed and a statement is prepared describing the basic features of the pattern. The pattern is then recognized by comparing this statement with a number of others already stored in the computer which relate to named patterns. Patterns are recognized independently of the angle at which they are presented to the scanner, and may be of any size provided that limits imposed by the resolution of the scanner are not exceeded. The average time to recognize a character is 60 seconds with the system programmed on a medium-speed computer. Special-purpose equipment built to perform certain of the stages of the process, together with the use of higher-speed computers now envisaged, will reduce this time by at least a thousandfold. If a new pattern is presented to the machine it will indicate its inability to recognize the pattern, but by giving the machine the name of the pattern, it may become one of the standard patterns which it can subsequently recognize. All the patterns recognized by the machine are hand-drawn and consist of such symbols as the capital letters of the alphabet and numerals, although the system is in no way limited to any special set of characters. Using exactly the same method but with an increase in the degree of complexity, it will be possible for machines to read handwriting. Special allowances are made for imperfections in the patterns, including breaks and general ill-definition. Where there is some confusion and an unknown pattern resembles two or more of the standard patterns, the relative degrees of similarity of the unknown to each of these standard patterns is printed out by the machine. View full abstract»

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  • Operating experience with a transistor digital computer

    Page(s): 222 - 228
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1109 KB)  

    A small digital computer using transistors as the only active circuit elements has been operating for a year. The paper describes the performance of this computer and, in particular, the failure rate of point-contact transistors. Earlier information on this computer is supplemented by details of circuit developments. View full abstract»

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  • A new high-speed digital technique for computer use

    Page(s): 229 - 236
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1154 KB)  

    A new method is described for realizing logical functions using square-loop ferrite cores and transistors. Complex circuits can be built up from identical elements, each consisting of one core, one transistor, three diodes and one resistor. The technique differs from earlier methods in that the current required to set a core to the `1¿ state is derived from a common supply and not from a previous stage. The control of digit transfer between stages is effected by a transistor whose collector and emitter are connected across one winding of the core. When a `1¿ is to be set in the core, the transistor is arranged to appear as an open-circuit, in which condition flux reversal is possible; when a `0¿ is to be set, the transistor appears as a short-circuit preventing reversal of flux. The core is reset to `0¿ at a controlled rate, producing a standardized voltage across the output windings. Logical operations are carried out by the analogue addition of these voltages. The system requires only two low-voltage d.c. supplies and is tolerant of voltage and component variations. It operates reliably at digit rates of 500kc/s. The paper also describes an experimental application of the method, designed to test its performance. View full abstract»

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