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Electrical Engineers, Proceedings of the Institution of

Issue 8 • Date August 1963

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Displaying Results 1 - 25 of 31
  • Design of wide-band degenerate parametric amplifiers for 3100 Mc/s

    Page(s): 1299 - 1303
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (553 KB)  

    Two degenerate parametric amplifiers for the frequency of 3100 Mc/s are described. The first is a single-resonator type with a bandwidth of 140 Mc/s, a gain of 19 dB and an excess noise temperature of 84°K. The second uses an additional resonant circuit to increase the bandwidth to over 300 Mc/s, but the excess noise temperature is also increased to 180° K owing to additional losses. The gain and bandwidth of the amplifiers are near optimum. View full abstract»

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  • Investigation of an experimental narrow-band parametric amplifier

    Page(s): 1304 - 1312
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    A comparison of theory and experiment has been made for a negative-resistance three-frequency parametric amplifier incorporating a single varactor diode, operating in the h.f. band. The effect of diode series loss resistance has been simulated simply by connecting resistors in series with the diode. Good agreement between theory and experiment, in relation to gain, bandwidth and noise figure, has been obtained when the direct current flowing through the diode is negligible. Effects associated with a significant direct current have been investigated. View full abstract»

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  • Analysis of parametric amplifiers incorporating varactor diodes

    Page(s): 1313 - 1318
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    A review is given of the capacitance and elastance approaches to the solution of the equations of circuits incorporating varactor diodes. An attempt has been made to set down a framework within which the approximations made in any particular analysis can be assessed. View full abstract»

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  • Video waveform correctors for use with coaxial cable

    Page(s): 1319 - 1328
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1204 KB)  

    Consideration is given to the problem of correcting for the effects of the attenuation/ and phase/frequency distortion of a coaxial-cable pair on the transmission of video waveforms. A method of designing correcting networks is described which uses an adjustable waveform corrector to provide the component values for a fixed network whose design tolerances are arranged to give the minimum waveform distortion. Using this method, the design of waveform correctors for use with coaxial cable becomes a rapid and straightforward operation. View full abstract»

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  • Video transmission system for use with coaxial cable

    Page(s): 1329 - 1340
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1762 KB)  

    A description is given of a video transmission system capable of transmitting 625-line monochrome television signals with very low distortion on coaxial-pair cable over distances of up to 25 miles, possibly extensible to more than 50 miles. Because power for intermediate repeaters is not fed over the coaxial-pair cables, the use of the system may be restricted under some circumstances. Special techniques are used for the reduction of hum and low-frequency interference and for the waveform correction of the coaxial-pair cable. The system is designed on a waveform basis with the minimum reference to steady-state characteristics. View full abstract»

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  • Colour performance of the Secam colour television system

    Page(s): 1341 - 1349
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    The Secam colour television system has many parameters in common with the N.T.S.C. system, but the constraints imposed on the reproduction of both large-area colour and colour transitions by the practical limitations on amplitude and frequency excursions are different. After discussing the parameters of the Secam system which have been assumed throughout the paper, the relationship between the chromaticity of the transmitted colour and the modulation of the subcarrier is considered and compared with the relationship which exists for the N.T.S.C. system. In particular, the effect of luminance level on the gamut of reproducible chromaticities is examined, and it is shown that the frequency limitations on the deviation of the Secam subcarrier are not important in so far as they might be expected to limit the practical colour gamut. The chrominance resolution of the system is discussed, and the use of an asymmetric passband for the colour subcarrier is suggested. The effects on the colour picture of some types of signal defect are mentioned. View full abstract»

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  • Reading charge images off the storage surface of a camera tube

    Page(s): 1350 - 1364
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1970 KB)  

    The basic principles involved in reading the charge image which is stored on the insulating surface of the target in a camera tube are discussed. The relative importance of various sources of noise is investigated, choice of optimum frequency response depends on the detailed View full abstract»

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  • Angular-dependent modes in circular corrugated waveguide

    Page(s): 1365 - 1373
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (941 KB)  

    The paper gives an account of an investigation, both theoretical and experimental, of angular-dependent EH11 modes in a circular corrugated waveguide. The investigation was undertaken because oscillation in a mode of this type has been shown to be the cause of pulse-shortening or beam blow-up troubles occurring in electron linear accelerators under certain high-beam-current conditions. It is shown that the dispersion characteristics can represent either forward waves or backward waves dependent on the dimensional parameters, and under certain conditions there can be a changeover from one to the other within the pass-band. There are marked similarities between these results and those found theoretically by other workers, for hybrid modes in a circular waveguide containing a coaxial dielectric rod. The measurements also include the distribution of magnetic and electric fields in the axial region, using perturbation techniques. Series impedance values (relating fundamental electric field intensity to power flow) are derived, and are comparable with the theoretical results. They confirm that in a linear accelerator an EH11 oscillation need only build up to a power level of the order of kilowatts to account for the disruptive effect on the beam observed during pulse shortening. View full abstract»

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  • Wideband technique applied to h.f. transmitter station equipment

    Page(s): 1374 - 1384
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    The application of wideband technique to h.f. transmitters is described. The particular band dealt with is 2¿27.5 Mc/s, but the findings are not restricted to this band. The general principles of wideband power amplification are discussed, followed by a description of, and results obtained with, a 1 kW wideband amplifier which uses a modified distributed-amplifier technique. This not only permits better utilization of valves, but the amplifier is also less sensitive to varying output-load conditions. The amplifier may be used on a number of frequencies simultaneously. The use of wideband stages in conjunction with tunable stages in very-high-power transmitters is advantageous. The retuning of drives for a frequency change is avoided by the wideband mixer, which accepts an intelligence signal at 3.1 Mc/s and a frequency-determining signal, giving an output at the desired radiated frequency. Wideband transformers use ferrite cores, and introduce very small power loss. Transformers with a power rating of 40 kW are in use. The availability of wideband equipment simplifies the operation of transmitting stations. An arrangement particularly suitable for ground stations in air communication is described as an example of one of the many ways in which wideband equipment can be used. View full abstract»

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  • Modern trends in high-frequency transmitter design

    Page(s): 1385 - 1394
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1455 KB)  

    The operating costs of a transmitting station can be substantially reduced if the equipment is automatically tuned and all services are directly controlled from a central point. This is due to the reduction of operating staff covering three shifts, and to the saving in `off the air¿ time made possible by rapid change of frequency. The paper describes a range of transmitters with output powers up to 85kW which have completely automatic control of tuning, coupling and gain. The transmitters are of the linear-amplifier type, and hence are suitable for all forms of service used in h.f. communication, when associated with the appropriate signal source. In particular, the paper describes the automatic control system of the transmitter. Various aspects of performance are discussed, including the design requirements for low distortion and for the reduction of spurious and harmonic emissions. If the saving in operating costs is to be fully realized, a high standard of reliability is necessary. The types of components used are described. They include variable vacuum capacitors, variable inductors, silicon rectifiers and vapour-cooled valves. View full abstract»

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  • Medium- and high-power automatically tuned linear amplifiers

    Page(s): 1395 - 1401
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1113 KB)  

    The essential features of any communications transmitter are reliability, ready means of frequency changing and linearity. Recently developed high-gain power valves require 1 kW, or less, driving power, which can be obtained from untuned wideband stages instead of the usual tuned drives. With only one tuned stage, it is easy to obtain a high degree of linearity, and automatic tuning by a frequency-following system becomes particularly attractive, without being unduly complex or expensive. A continuous frequency-following system with automatic loading control offsets changes in feeder impedance, so that the final amplifier is always operating under optimum conditions. This is a great advantage compared with preset systems. The design of compact, self-contained equipments, requiring no special under-roof ducts for air or cables, simplifies installation, particularly in existing buildings where new equipments replace obsolescent types. For new buildings the cost can be kept to a minimum. The paper details the electrical design principles for 7¿ and 30 kW automatically tuned linear amplifiers that contain wideband driving stages. The mechanical design is discussed and also the arrangement of suitable servo-tuning and rectifier circuits. Final specification figures and some typical test results are given. View full abstract»

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  • Choice of multi-channel telegraph systems for use on H.F. radio links

    Page(s): 1402 - 1410
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1163 KB)  

    Telegraph systems for use over h.f. radio links are generally restricted to low modulation rates (100¿200 bauds) because of the effects of multi-path propagation. The usual practice is to employ frequency-division multiplexing to exploit the bandwidth of the radio channel. Different methods of modulation in the telegraph channels may be used¿frequency-shift, frequency-exchange and phase-shift. The performance of typical systems of each kind has been measured in the laboratory under similar conditions of propagation provided by a fading-circuit simulator with additive uniform spectrum random noise. The relative merits of the systems are discussed in relation to transmission accuracy and bandwidth utilization. These are found to vary according to propagation conditions and to whether automatic error correction is used or not. View full abstract»

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  • Developments in long-distance H.F. point-to-point communications

    Page(s): 1411 - 1420
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    The paper surveys technical developments in the point-to-point h.f. communication system of the British Post Office. In the first part, the development of radio-telegraph systems is discussed, and it is shown that these are tending to standardize on multichannel voice-frequency systems, using 2-tone for normally difficult routes (e.g. long routes subject to severe multipath effects) and narrow-band frequency modulation on the easier routes. Similarly, the development of radio-telephone systems is considered, and it is shown how the efficiency of these can be improved by the use of 4-wire privacy, with consequent simplification. The successful application in radio-telephony systems of a syllabic constant-volume amplifier, in conjunction with a complementary device at the receiving end regulated by a separate control channel, should-further increase their efficiency and may enable the radio terminals to be regarded as simple repeater stations. The second part describes modern systems which are to be provided at the rebuilt Leafield transmitting and Bearley receiving stations of the Post Office. The Leafield station will have two groups of six 30kW linear self-tuning transmitters, remotely controlled to radiate any of 25 synthesized frequencies and to have access to 10 aerial systems, each comprising two or three rhombic aerials. The Bearley station will have capacity for a large number of remotely controlled receivers with synthesized frequency control. New receivers will be of transistorized design, and the closer frequency tolerance provided by synthesized frequencies should, eventually, enable automatic frequency correction (a.f.c.) to be eliminated. It is planned to extend the control of the stations to the traffic terminals in due course, and this, together with the increased reliability of equipment which the fullest use of semiconductor devices is expected to bring, could lead to substantial economy in staffing. View full abstract»

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  • Highly stable frequency-shift-keying exciter

    Page(s): 1421 - 1424
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (454 KB)  

    The provision of a frequency-shift-keying system to meet present-day requirements presents the designer with three main difficulties; (a) the attainment of sufficient stability of the centre frequency, (b) the provision of a system suitable for keying at high digit rates, and (c) the prevention of out-of-band radiation. The paper indicates some problems inherent in systems commonly used in which the solution is often a compromise. A system is described in which a crystal-controlled master oscillator is used, and half the required shift frequency is added to, or subtracted from, the oscillator frequency by means of a pick-up coil turning in a rotating r.f. field. The method has the advantage that the stability of the frequencies of transmission is not appreciably degraded as in the case of frequency-pulled oscillators. Also, because the mark and space frequencies do not exist together, the problem of suppressing the alternative frequency does not arise, as in systems in which both frequencies are generated separately. After the f.s.k. signal has been generated at a convenient frequency, a second crystal-controlled oscillator converts it to the particular carrier frequency required. Out-of-band radiation is reduced by synchronizing the shift frequency with the basic square wave of the telegraph digits and correctly phasing it: this can easily be achieved with automatic telegraphy. In conclusion, a practical system including some design features is given. View full abstract»

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  • Connecting large machines to power systems

    Page(s): 1425 - 1433
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2226 KB)  

    There are several methods of connecting machines to systems, each method having its advantages for particular types of machine and specific system conditions. Whereas, in the past, limitations were imposed only on the characteristics of the machine during the process of connection attempts are now made to assess the mutual effects between the system and the machine and to make allowance for these. On large and important systems involving large machines it is becoming apparent that a thorough study of the problem of connection may result in a more economic and technically superior arrangement than has been used in the past. Several factors may be involved during machine connection; these include switching surges, voltage reductions caused by starting currents, acceleration effects with possible current pulsations and synchronizing effects. The significance of any, or all of these, on the system is determined by the consequent effects on other machines or apparatus connected to the system is on the machine itself. A combined analysis of the machine and local system is the only satisfactory way to determine the limiting factors which can be improved most economically, and so enable the most satisfactory combination of apparatus and starting method to be selected for any particular installation. View full abstract»

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  • Multi-phase rectifier currents

    Page(s): 1434 - 1440
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (617 KB)  

    The paper deals with a modified theory of multi-phase rectifier currents. This theory is based on the fact that all system currents, i.e. the rectified secondary line and phase, as well as the primary, currents in the feeding transformer, depend algebraically on the harmonics of the current through a single rectifier element. It suffices, therefore, to know all components of this current in order to compute the currents in all rectifier circuits. After a classification of all rectifier connections into three groups, the `element¿ current is computed and the above-mentioned proof given. The theory provides closer insight into the rectification mechanism, is very easy to apply, is more exact, and permits calculation of the torques produced in d.c. machifles by higher-current harmonics or the heating of rectifiers. View full abstract»

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  • Switching drive of induction motors

    Page(s): 1441 - 1450
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1086 KB)  

    Recent developments in semiconductors lead to new possibilities of motor control in general and of the induction motor in particular. The latter type of motor, although the most simple in construction and therefore the most widespread in use, does not lend itself easily to speed control and feedback arrangements. The paper shows that electronic control by means of semiconductors of the thyratron type is easily adaptable to speed-control requirements. This type of control, based on switching currents by semiconductor devices, is applied first to the stator circuit and secondly to the rotor circuit. In the former case a squirrel-cage motor can be used, but the rotor control circuit will show certain advantages. View full abstract»

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  • Phase-plane techniques for the solution of transient-stability problems

    Page(s): 1451 - 1461
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    The paper presents a graphical-numerical method for determining the transient stability limits of a two-machine system under the usual assumptions of constant input, no damping and constant voltage behind transient reactance. The method presented is based on the phase-plane criterion,1, 2 in contrast to the usual step-by-step and equal-area methods. For the transient stability limit of a two-machine system, under the assumptions stated, the sum of the kinetic energy and the potential energy, at the instant of fault clearing, should just be equal to the maximum value of the potential energy which the machines can accommodate with the fault cleared. The assumption of constant voltage behind transient reactance is then discarded in favour of the more accurate assumption of constant field flux linkages. Finally, the method is extended to include the effect of field decrement and damping. A number of examples corresponding to each case are worked out, and the results obtained by the proposed method are compared with those obtained by the usual methods. View full abstract»

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  • Magnetic field problem with axial symmetry and its solution in terms of Fourier-Bessel expansions

    Page(s): 1465 - 1472
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (802 KB)  

    A method for reaching implicit analytical solutions is explained, demonstrated and verified for certain problems of potential theory, characterized by having boundaries which are parts of co-ordinate surfaces. Different Fourier expansions for the potential are matched over an interface of the problem by the solution of linear simultaneous equations in their coefficients. Two problems are completed by numerical computations and the construction of equipotentials. Comparisons are made with known results for the easier problem, and with experimental results for the other. The method is considered as a computational alternative to relaxation and finite differences, and the axisymmetric problem is shown to be aimed at applications in the design of electrical machines. View full abstract»

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  • Influence of parasitic brush currents on the performance of D.C. generators

    Page(s): 1473 - 1479
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    The parasitic brush currents which flow in the armature coils short-circuited by the brushes at the moment of commutation modify the characteristics of a d.c. generator, and the effects are particularly noticeable when the speed is varied. The modification of the characteristics can be explained by representing the parasitic brush currents by a current flowing in an additional armature circuit subject to rotationally generated voltages. The pattern of behaviour predicated by the theory is in good agreement with the machine characteristics obtained by test. Although the theory is expressed in linear terms, it nevertheless explains phenomena which are significant in the practical performance of machines. View full abstract»

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Aims & Scope

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

Full Aims & Scope