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Electrical Engineers, Proceedings of the Institution of

Issue 3.4 • Date March-April 1971

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Displaying Results 1 - 25 of 40
  • Simple estimators for error probability in simulation studies of digital communication systems

    Publication Year: 1971 , Page(s): 397 - 400
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (445 KB)  

    The paper describes the application of some statistical estimation techniques to the problem of evaluating the probability of error of (digital) communication systems. The usefulness of an estimator is governed by the variance of the estimate, which, in this case, is the measured probability of error. It is shown that, for the low values of probability of error considered to be practically useful, simple sample-mean estimation requires somewhat large numbers of statistical trials to give results of low variance. The number of statistical trials, however, may be decreased by the use of simple control or antithetic estimators. View full abstract»

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  • Subjective evaluation of unsuppressed echo in simulated long-delay telephone communications

    Publication Year: 1971 , Page(s): 401 - 408
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1040 KB)  

    The paper describes an experiment to measure the subjective effect of unsuppressed echo to determine the improvement in echo return loss required of echo cancellers in long-delay telephone communications. Using a simulated long-delay telephone connection of 16.5 dB nominal overall reference equivalent, tests were carried out over a range of conditions in which the 1-way delay varied between 50ms and 600ms, and the echo return loss between 15 dB and 50 dB. Echo-path frequency characteristics which an echo canceller might cause in practice were represented by a flat characteristic and a charactereistic decreasing in loss with increasing frequency. Because of the large number of test conditions (40) in the experiment, the experimental design is unique and is described. View full abstract»

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  • Limitations of error-detection coding at high error rates

    Publication Year: 1971 , Page(s): 409 - 416
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1239 KB)  

    The paper seeks to justify the contention that the efficiency of error-detection-coding techniques is frequently overestimated owing to insufficient appreciation of the interaction between the characteristics of the code and those of the signalling channel itself. The redundancy of an error-detection code (e.d.c.) requires an increase in modulation rate, and this causes an increase in element error rate due to reduction in normalised signal/noise ratio. On h.f. radio circuits, ionospheric effects can cause even greater increases, and current interleaving and convolution techniques only recoup a small proportion of the disadvantage. It is shown that, in many cases, these factors can outweigh the correcting capabilities of current codes. Comparison of various binary codes and the Piccolo m.f.s.k. system suggests that, where circumstances are such that extremely low error rates are not essential, a nonredundant unprotected code may be comparable in availability with an e.d.c., and Piccolo would probably be an improvement. View full abstract»

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  • Correlation-recovered adaptive majority multiplexing

    Publication Year: 1971 , Page(s): 417 - 422
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (714 KB)  

    A novel method of multiplexing based on a pattern-recognition technique is described, in which binary data are combined for transmission over a common medium by modulation onto binary codewords. A majority-logic gate forms the transmitted (binary) signal from the modulated codewords. Demodulation is effected by a correlation process using digital matched filters. The system exhibits an adaptive property in the relationship between the channel error-correcting properties and the number of channels in use. Theoretical and experimental results are reproduced, and a description of a prototype equipment is included. View full abstract»

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  • Loudness ratings of telephone speech paths

    Publication Year: 1971 , Page(s): 423 - 436
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2094 KB)  

    Telephone engineers rely a great deal on loudness ratings of speech paths for the framing of national transmission plans and for international recommendations to secure proper co-ordination between national networks. Loudness ratings for such use are, by convention, based on subjective loudness comparisons against a specified high-quality reference system (NOSFER), and the measurements are difficult to reproduce accurately. A great deal of work has already been done to enable such ratings (called `reference equivalents¿) to be determined, by calculation from instrumentally measured sensitivities of the telephone sets and local lines. However, little practical use can be made of these results because of a lack of properly specified instrumental measuring methods. The situation may improve when international agreement has been achieved on the characteristics and method of use of artificial mouths and artificial ears for telephony. The paper presents a review of available fundamental information marshalled into a form convenient for use as soon as suitable electroacoustical measuring methods have been defined and accepted. The precision and reliability of loudness ratings can also be improved by replacing the wideband reference system by an `intermediate reference system¿ more like the commercial telephone equipment to be tested. Particulars suitable for such a system are suggested. View full abstract»

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  • Application of fourier techniques to computer-aided design of electronic systems

    Publication Year: 1971 , Page(s): 437 - 446
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1424 KB)  

    At an early stage in the design of electronic systems, decisions have to be made concerning the function and performance of certain vital elements in the main signal path of the system, such as modulators and crucial filters. WASP (waveform and spectral-analysis program) is a computer program which allows the user to analyse a proposed system of cascaded modules and to extract the waveform and spectrum of the signal at any point in the chain. The program exploits the fast Fourier transform to calculate the spectrum at the output of the successive blocks of the system. The progress of the calculation is controlled by a simple set of orders, which are provided by the user as part of his data. The method is applicable to radar, communications, sonar and control systems, and the paper uses, as an example, the design of a digital f.m. radio system. View full abstract»

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  • IEE Scottish Electronics & Control Section: Chairman's address. Public telecommunication in Britain

    Publication Year: 1971
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (144 KB)  

    First Page of the Article
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  • Automatic compensation in colour television cameras for changes in scene illuminant

    Publication Year: 1971 , Page(s): 449 - 459
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1408 KB)  

    Prototype equipment is described which automatically corrects the colour balance of a colour television camera for changes in the scene illuminant. The performance of this equipment, which is assessed over a wide range of illuminants, shows that a satisfactory degree of automatic control may be obtained in practice. View full abstract»

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  • Electronic field-store standards convertor

    Publication Year: 1971 , Page(s): 460 - 468
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1337 KB)  

    An electronic field-store standards convertor is described which converts colour-television signals on the American 525-line standard to signals on the European 625-line standard. The convertor was first introduced into service by the BBC to give coverage of the Mexico City Olympic Games. View full abstract»

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  • Design of complex microstrip circuits by measurement and computer modelling

    Publication Year: 1971 , Page(s): 469 - 474
    Cited by:  Papers (11)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (794 KB)  

    Measurement techniques have been developed which allow the complex admittance existing at a nominal microstrip open circuit to be accurately characterised. This information, together with the line loss and wavelength, has enabled the electrical defining plane of a shunt stub to be determined. By using a circuit-design technique based on computer modelling it is possible to allow for all these factors. When this approach was applied to the design of a filter with 13 elements, the computer element lengths, when fabricated in microstrip, produced a filter with a bandpass characteristic to within 1% of the computer-modelled response. The need for cut-and-try development is therefore virtually eliminated. The technique of exact computer modelling has also been applied to oscillator circuits, using varactortuned Gunn devices. These circuits are extremely complicated, since they employ waveshaping of the voltage applied to the device. The second harmonic is trapped in a carefully controlled independent resonant circuit. For certain devices, this technique can increase the microwave output power by a factor of 4 or 5. Without the use of cut-and-try methods, devices have operated only 5MHz away from the designed output frequency of 6GHz. View full abstract»

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  • Use of tests at elevated temperatures to accelerate the life of an m.o.s. integrated circuit

    Publication Year: 1971 , Page(s): 475 - 485
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1546 KB)  

    Assurances of a long service life will often be demanded of m.o.s. integrated circuits used in telecommunication equipment. An attempt has accordingly been made to identify failure risks and devise life-prediction procedures by accelerated testing, ambient temperature being the primary stress variable. The test vehicle, manufactured on a volume production line, had a simple circuit configuration permitting direct access to its constituent transistors and allowing each of them to be operated under different electrical conditions. The parameters monitored included threshold voltages, both of the transistors and of a spurious device, gain factors, transistor resistances (in the conduction mode), leakage currents and protective-diode breakdown voltage. The most significant response was obtained from the transistor threshold voltages, which change substantially but in a manner consistent both with the electrical operating conditions and with known physical theories of charge instability in the m.o.s. system. It is suggested that at least the drift of transistor threshold voltage is amenable to a life-prediction procedure, and it is shown how the results could be exploited for procurement-specification purposes. View full abstract»

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  • Analogue recursive computer

    Publication Year: 1971 , Page(s): 486 - 492
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (937 KB)  

    A control computer is described which uses a serial digital program to control an arithmetic unit and storage system working entirely in the analogue mode. Storage is capacitive, using field-effect-transistor switches for data selection. Using conventional techniques, speeds of 20¿s per arithmetic operation are readily obtainable. The first application of this computer is to aircraft-gas-turbine control. A control program, for example, of a Rolls Royce Olympus 593B engine occupies 120 instructions, and the computation has a recursion time of 3ms. An accuracy of within 0.1% is obtainable. View full abstract»

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  • Design of large high-speed floating-point-arithmetic units

    Publication Year: 1971 , Page(s): 493 - 498
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (858 KB)  

    An investigation of the design philosophy of large floating-point -arithmetic units has been undertaken, with a view to establishing the principles for constructing such a unit for a large high-speed computing system. The main consideration applied was maximum speed for a reasonable cost in a machine handling numbers 30¿64 bits in length. Consideration of compatibility with other systems was specifically excluded, although the unit to be implemented does take this factor into account. Within these constraints, it is shown that negative numbers should be represented in twos-complement form. Numbers of upto 64 bits in length would be handled, with the binary point at the less significant end of the mantissa. Rounding should be performed by forcing a `carry in¿ to the least significant bit when the answer is more than single length, sufficient information being retained to enable multilength arithmetic to be implemented. Answers should not be normalised. The data presented are sufficient to indicate the effect of applying different criteria. View full abstract»

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  • Design of large high-speed binary multiplier units

    Publication Year: 1971 , Page(s): 499 - 505
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (786 KB)  

    An attempt has been made to review the methods of multiplication available for use in a large high-speed computing machine. Number lengths of 50 to 60 bits and multiplicatiion times of less than 0.5 ¿s were the design aims. Suitable multiplier units will make use of carry-save adders to reduce the time for each addition cycle, and will decode several multiplier bits in each cycle to reduce the number of cycles required. The number of carry-save adders to be used is set largely by economic considerations. The number of multiplier bits to be decoded in each cycle is determined by the time required to form multiples of the multiplicand prior to cycling. It is shown that the best compromise between cost and speed is achieved if two or three carry-save adders are used in a serial-parallel configuration, and three or two multiplier bits are decoded in each cycle, respectively. A comparison with several other multipliers is made. A method for incorporating carry assimilation at the less significant end of the product is described, thus requiring the final propagate addition to be only single length, while still retaining the full double-length result. An indication of the effect of number length on the conclusions is inclued, but is not worked out in complete detail. View full abstract»

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  • Theory of cylindrical antennas in conducting media

    Publication Year: 1971 , Page(s): 507 - 510
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (442 KB)  

    A method is presented for analysing isolated symmetrical dipoles and two such parallel nonstaggered dipoles immersed in a homogeneous conducting medium. The results obtained by the present theory are in good agreement with experimental results. The theory is restricted to relatively thin dipoles, and the lengths of the dipoles should not considerably exceed the operating wavelength measured in the conducting medium. An interesting conclusion is reached that the usefulness of the idealised delta-function generator, commonly used in the linear-antenna theory, is restricted to media for which, approximately, ¿/¿¿<1. View full abstract»

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  • Simple method of antenna analysis leading to the mode-theory results

    Publication Year: 1971 , Page(s): 511 - 514
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (445 KB)  

    A method of antenna analysis is presented which gives the current distribution and input impedance of finite conical antennas. The results for the impedance are identical with those obtained from the 'mode theory', but the results for the current have the advantage that they are found in closed form. In addition, the method is much more easily applied. A very general method of obtaining the characteristic impedance of an antenna which is a section of a spherical transmission line is also described, and this method is applied to the folded triangular monopole. View full abstract»

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  • Ground-interference pattern of 16kHz radio waves during summer days

    Publication Year: 1971 , Page(s): 515 - 518
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (391 KB)  

    Results are presented from measurements of the signal strength made in an aircraft flying northwards from the 16kHz transmitter GBR, Rugby, England, on four days in June 1969, near the epoch of maximum, solar activity. The interference pattern due to the combination of ground and sky waves is found to change significantly with local time, whereas the change between different days at the same local time is small, even though the conditions of magnetic and solar activities have changed. This implies that, for the present observations, the influence of the Sun's position was more marked than that of the magnetic or solar conditions. The pattern is similar to, but extends, those of Budden, Ratcliffe and Wilkes3 and of Weekes4, which were also made at solar maximum. View full abstract»

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  • High-power radar for meteorological stuides in clear air

    Publication Year: 1971 , Page(s): 519 - 528
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1733 KB)  

    A very high-sensitivity S band radar capable of detecting targets with radar cross-section of 5 × 10¿10 m2 of reflectivities of 2 × 10¿15 m¿1 at a range of 10km has recently been brought into operation for meteorological studies of the clear atmosphere. The paper outlines the constraints set by the meterological requirements, and describes the radar which has been assembled to meet them. Examples are presented of clear-air echoes obtained both from extensive horizontal layers at hieghts up to 3 km, and also from high-altitude clear-air turbulence. View full abstract»

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  • Airgap winding for large turbogenerators

    Publication Year: 1971 , Page(s): 529 - 535
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1069 KB)  

    Modern turbogenerators have large airgaps for system stability. This airgap space can be used to accommodate the a.c. windings of the machine, instead of placing them in slots. In the paper, the disadvantages of windings in slots are discussed, together with problems that will result from putting the winding in the airgap. Using a published design for a conventional 750 MW machine and converting this to an airgap-winding design, it is shown that the size and weight of the total machine are considerably reduced, with corresponding reductions in cost and transportability. Since it is desirable that a practical airgap winding should pass through the stator bore, so that it can be prefabricated as a complete cylinder, the normal winding is discussed and is shown to be difficult to make as a cylinder. A concentric winding, proposed by the author, which has normal winding factors in the active region and which can be made as a cylinder, is described. Simplified calculations for forces between phase bands and for leakage reactance are given. These forces will have to be calculated in detail later, but the simplified calculation shows that they can easily be contained by modern reinforced resins. The leakage reactance is shown to be considerably reduced; this is important as an indication that there will be little need for transposition in the radial direction. A simple method of threading the rator through the airgap winding is described. View full abstract»

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  • IEE North Staffordshire Sub-Centre: Chairman's address. L.V. motor-control centres; their development and some design aspects

    Publication Year: 1971
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (133 KB)  

    First Page of the Article
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  • Induction-motor speed-control schemes employing stator-voltage variation and pole-change windings

    Publication Year: 1971 , Page(s): 537 - 542
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    The paper considers the advantages which may be obtained by introducing pole-change windings into squirrel-cage induction-motor speed-control schemes employing stator-voltage variation. It is concluded that, in certain specified cases, a significant increase in the range of operation may be obtained for a given dissipation of rotor power. View full abstract»

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  • Effect of skewing slots on flux distribution in induction machines

    Publication Year: 1971 , Page(s): 543 - 549
    Cited by:  Papers (15)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (974 KB)  

    Although skewing is practically the rule for all but the largest induction motors, its effect on the flux distribution has received little attention. It is shown by experiment that the effect of skewing can be very significant and results in a poorer performance. Some of the advantages which are commonly believed to accrue from the use of skew are fictitious if a proper choice of slot combination is made; these are discussed. View full abstract»

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  • Novel method for reversal of single-phase squirrel-cage induction machines

    Publication Year: 1971 , Page(s): 550 - 554
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (554 KB)  

    Several systems have been devised for the reversal of single-phase induction motors, the majority of which utilise quadrature, or approximately quadrature, stator windings. However, if the windings are constructed so that their axes are at an angle considerably less than 90° electrical, an alternative method of reversal can be obtained. Auxiliary-winding design criteria are developed for this novel method of reversal, and computed theoretical results are compared with test results for an experimental design of a split-phase start motor. It is demonstrated that this novel method has performance features which make it preferable to the other reversal systems of single-phase motors for ertain application. View full abstract»

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  • Rating of conductors for short-duration currents

    Publication Year: 1971 , Page(s): 555 - 570
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1726 KB)  

    The heat equation for the mean temperature of a conductor carrying a short-duration current is solved for adiabatic conditions at the surface and for all the relevant thermophysical properties varying quadratically with temperature. A simplified approximation to the solution is also given. Curves showing the variation of temperature with energy input and with the time integral of the square of the current density ¿ J2dt are presented for various conducting materials. These are in fair agreement with experimental data. Equations are given for calculating ¿ J2dt for various time-dependent current forms. It is shown from the measured prearcing energy and ¿ J2dt that, for current densities in the ranges 108¿1012 A/m2 and rupture times down to a few microseconds, the conductor rarely melts completely before rupture, owing to the radial temperature gradient, the loss of mechnical strength and the effect of electromagnetic forces. With rupture times faster than 1¿s, complete melting and even vaporisation can occur, because inertia and magnetic forces tend to cause the conductor to retain its physical shape. A method is given for calculating the loss of tensile strength of conductors subjected to repeated current transients. View full abstract»

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  • Erratum: Economic comparisons in planning for electricity supply

    Publication Year: 1971
    Save to Project icon | PDF file iconPDF (119 KB)  
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Aims & Scope

The Proceedings of the Institution of Electrical Engineers was published by the IET between 1963 and 1979.

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