摘要:

Loudness ratings of local telephone circuits are essential quantities in planning national telephone networks and in co-ordinating international telephony. At present, these have to be obtained by subjective testing, which is laborious, expensive and not readily reproducible except in particularly well equipped laboratories. Methods are also available (and in use for certain purposes) for obtaining loudness ratings by calculations and by instrumental measurements, but, to ensure uniform results, it is necessary to secure agreement on precise definitions of certain items so that the principles can be implemented equally well, to yield the same numerical values, by calculation and by objective instrumentation as well as subjectively. A new set of definitions is proposed. These are similar to those already examined and adopted provisionally by the British Post Office. Further examination of certain aspects is being carried out in the CCITT laboratory by experiments which include subjective tests, calculations based on frequency-response measurements with artificial mouths and artificial ears and by objective instrumentation which uses a special signal generator and a voltmeter. Results are showing that, with suitable precautions, the ratings can be made practically independent of the method of implementation. An important feature of such a unified set of principles will be the possibility of making confident theoretical estimates of the performance of hypothetical local telephone circuits which might later be realised in service. Thus, design, development, acceptance testing and maintenance of telephone equipment could, probably for the first time, be based on common fundamental principles.

DOI:10.1049/piee.1972.0284

出版商:IEE    

年代:1972

数据来源: IET

摘要:

The application of digital methods to the internal distribution of high-quality sound signals in a broadcasting system allows a high and predictable standard of technical quality to be maintained with the minimum of attention by operating staff. Pulse-code-modulation systems for the incorporation of a sound signal into a video waveform and for the multiplex distribution of programmes for the radio service will soon be in operation within the BBC, and the eventual use of national and international digital links for this purpose is envisaged. The feasibility of digital recording has also been demonstrated. This paper is mainly concerned with the special requirements to be met in the digital coding and decoding of broadcast-quality sound signals. Considerations of quantising noise, distortion and digit-error detection lead to a bit rate approaching half a megabit per second per channel, though this rate may be somewhat reduced as a result of current developments in digital companding. No attempt is made to deal with aspects of point-to-point transmission which are common to other digital systems, but the effects of digit-error rate and of timing jitter are considered, and tolerances are suggested.

DOI:10.1049/piee.1972.0285

出版商:IEE    

年代:1972

数据来源: IET

摘要:

The chain parameters of five well known regular nonuniform transmission lines (n.u.t.l.s) are evaluated. In these evaluations, the differential interrelations among the chain parameters of the n.u.t.l.s. in the form of 2nd-order matrix differential equations with their boundary conditions are employed. The method used is applicable to any nonuniformity, provided that the 2nd-order differential equations formed by the chain parameters have regular singularities.

DOI:10.1049/piee.1972.0286

出版商:IEE    

年代:1972

数据来源: IET

摘要:

The logic cellular array of a division device that is based on the SRT division algorithm extended to the case of redundant representation of the partial remainders is reported. In the paper, redundant binary representation of the partial remainders is due to the fact that any digit can have the following values: minus one (1), zero (0) and plus one (1). Comparison of the logic array proposed with other cellular logic arrays reported in the literature for binary division yielded that, with the former design, greater operating speeds may be attained.

DOI:10.1049/piee.1972.0287

出版商:IEE    

年代:1972

数据来源: IET

摘要:

Existing synthesis techniques are utilised to develop Tables of low-pass prototype element ‘g’ values of predistorted singly and doubly terminated first-kind 0.01 dB-ripple Cheby̅shev-filter networks with up to nine sections. Through conventional frequency-transformation techniques, corresponding bandpass circuits can also be realised. Excessive predistortion (low Q factor) will deteriorate the passband voltage standing-wave ratio, whereas the effects on stopband selectivity are insignificant. Further, the sensitivity of the prototype-element values becomes more acute as the requirement for predistortion is increased. The Tables may be used as a design tool for realising the optimum prescribed insertion-loss characteristics in practical microwave networks where the effects of parasitic component dissipation are critical.

DOI:10.1049/piee.1972.0288

出版商:IEE    

年代:1972

数据来源: IET

摘要:

Computer simulations are used to study the effect of envelope limiting on the performance of pulse-compression moving-target-indicator (m.t.i.) radar in the presence of clutter produced by stationary reflectors and nonstationary reflectors. It is shown that the use of pre-envelope concepts to deal with bandpass processes as complex lowpass envelopes enables efficient use to be made of high-speed fixed-point-computer fast-Fourier-transform (f.f.t.) techniques to investigate difficult nonlinear-radar-system problems.

DOI:10.1049/piee.1972.0289

出版商:IEE    

年代:1972

数据来源: IET

摘要:

An arbitrarily shaped aperture in the wall of a uniform waveguide of unspecified cross-section has been analysed in terms of its scattering and radiating properties, using variational techniques. The method is of general application, the principal requirement being that the Green's functions for the waveguide and the external medium or structure should be known. Attention is focused particularly on the problem of radiation into free space from a nonresonant narrow rectangular slot arbitrarily located in the broadwall of plane rectangular waveguide. Analytical expressions are presented for the transmission and reflection coefficients and the power radiated, and, where possible, the results are compared with those of other theories. An expression for the electric field in the slot has been derived, and this has been used to formulate rigorous conditions under which circular polarisation is radiated by crossed slots. The generally expressed conditions for circular polarisation are shown to be approximate only.

DOI:10.1049/piee.1972.0290

出版商:IEE    

年代:1972

数据来源: IET

摘要:

Nondimensional variables are described that take account of changes in flow geometry, gas velocity and pressure and arc current on the behaviour of axial-flow forced-convection arcs. Calculated steady-state characteristics are shown that are in good agreement with measurements made in nitrogen gas. An elementary theory is presented for the dynamic arc in nozzle flow that agrees qualitatively with the known behaviour of such arcs. The nondimensional scaling principle is extended to include the interaction between the arc and an electric circuit. It is shown that, for a simplified arc model, the zero-current energy balance of a given type of circuit can be described by a unique set of clearance/failure boundaries. Such a set of curves represents all combinations of gas-flow variables and circuit values.

DOI:10.1049/piee.1972.0291

出版商:IEE    

年代:1972

数据来源: IET

摘要:

Small changes in element parameters which can be caused by manufacturing tolerances, wear, aging, and maintenance can cause significant changes in the overvoltage performance of a power system in which they are incorporated. To study the effect of such dispersion on the performance, a computer-controlled transient-network analyser capable of rapid, accurate estimation of overvoltage-probability distributions has been developed. This system has been used to study the sensitivity of the probability distribution of overvoltage peaks to changes in circuit-breaker characteristics. The effects of prestrike, mechanical dispersion of contact-closure instants between phases, and preferred pole-closing sequences were investigated in typical networks using both plain and resistor-equipped breakers. Significant changes in overvoltage-probability distributions which could cause up to tenfold increases in line-flashover probabilities were found.

DOI:10.1049/piee.1972.0292

出版商:IEE    

年代:1972

数据来源: IET

摘要:

The paper describes tests involving sudden loss of generation on an isolated power system of more than 2000 MW installed capacity. Amounts of generation ranging from 3% to 27% of the system total were disconnected, causing voltage depression and frequency excursions. The maximum transient frequency drop recorded was 3.25 Hz. During the tests, measurements were made simultaneously at six different locations, five of which were concerned with load response, and the sixth with the (average) system frequency. Relatively homogeneous but different types of loads were selected, including residential, commercial, aluminum-plant mechanical-industry and electric furnace loads. The applied voltage and power flow to these loads were recorded during each system disturbance. Using data obtained from the tests, an attempt has been made to determine the characteristic parameters for the individual static loads. The test results and the experimental values of the characteristic parameters are presented and discussed.

DOI:10.1049/piee.1972.0293

出版商:IEE    

年代:1972

数据来源: IET