摘要:

The paper deals with an investigation that was carried out to determine whether simple data-compression techniques could be applied successfully to an experimental 9.6 kbit/s adaptive p.c.m. digital speech system: The main aim of the investigation was to ascertain whether compression factors of two or four could be achieved. In the paper, the results of the investigation are presented and it is shown that the adaptive p.c.m. system is converting speech into a 9.6 kbit/s digital form that appears to possess very little redundancy. The results of a statistical analysis of the data are given, and it is shown that a compression factor of two is unlikely to result in a speech quality that is commercially acceptable. The results of an experimental investigation that was carried out in support of the theoretical investigation are presented. The results of the experimental investigation show that although compression by a factor of two results in a speech quality that is commercially unacceptable, a 4/3 compression can be achieved without any serious degradation of the speech quality.

DOI:10.1049/piee.1976.0021

出版商:IEE    

年代:1976

数据来源: IET

摘要:

The polarisation of v.l.f. radiowaves reflected from the ionosphere at steep incidence has been determined from simultaneous measurements of the reflection and conversion coefficients. Changes due to the diurnal and seasonal variations in electron density are reported and the marked anomalies observed during sudden ionospheric disturbances produced by solar-flare activity are discussed.The propagation parameters have been calculated using the fullwave analysis for a number of idealised models of the electron density/height distribution. The calculated values are in close agreement with those obtained experimentally. It is suggested that these models could be used to determine the propagation parameters as an aid in the development of any new v.l.f. system.

DOI:10.1049/piee.1976.0022

出版商:IEE    

年代:1976

数据来源: IET

摘要:

Schwarz's iterative procedure of overlapping regions, which has been previously employed in the solution of polygonal waveguides and similar problems, is employed here to solve for the scattering matrix coefficients at the sharp junction of a sectoral and parallel-plate waveguides. It is shown that by dividing the junction into semi-infinite rectangular and sectoral subregions, and using the Green's functions of each, the problem is reduced to the solution of a system of integral equations of the Fredholm type. The scattering-matrix coefficients are computed and presented graphically as a function ofkb, together with the previously published data. The solution is relatively simple and the method is shown to be efficient since the fields are described in terms of rapidly convergent series (especially for a sectoral region of small flare angle), and accurate results are typically obtained after two or three iterations. It is shown that the method is applicable for sectoral regions of arbitrary flare angle, but a third circular subregion is particularly required for flare angles exceeding 180°.

DOI:10.1049/piee.1976.0023

出版商:IEE    

年代:1976

数据来源: IET

摘要:

Recent work in the areas of combinatorial logic-design theory and logic-gate circuits is leading to new concepts of logic-network realisation. In the paper, the multioutput threshold-logic gate is considered as a powerful configuration for future use both in s.s.i. package form and also for internal m.s.i./l.s.i. subsystem use. Design techniques to always fully utilise its logic power, particularly for multifunction applications, are, however, still awaited, although techniques which may be applied for simple networks are discussed, together with the possible line of further research in this area of increasing significance.

DOI:10.1049/piee.1976.0024

出版商:IEE    

年代:1976

数据来源: IET

摘要:

Increasing use will be made of multifault-(n-fault-) tolerant systems, i.e. systems whose performance is unaffected by any arbitrary combination ofnfaults. The paper presents a family of fundamental fault-tolerant systems using standby spares. Recursive algebraic expressions are given both for the smallest combinations of disabling failures and for the probabilistic reliabilities of each system in the family. It is shown that multifault tolerance by itself is not exactly synonomous with a best reliability or a best cost/benefit parameter. The ‘crossover’ surface of any redundancy is defined as the infinite set of all combinations of component reliabilities (as they decrease) for which the reliability of the redundant system has deteriorated to the same reliability as the nonredundant system. For component reliabilities outside the ‘crossover’ surface, the presence of the redundancy further decreases system reliability. This fact is established numerically forn=6. The 3-failure-tolerant system was proposed for an aerospace application, but in a slightly modified form. This modified form would tolerate only two failures of the most highly reliable components, but three failures of the least reliable components.

DOI:10.1049/piee.1976.0025

出版商:IEE    

年代:1976

数据来源: IET

摘要:

The paper describes a method of minimising the material cost of small, 3-phase, cage-rotor, induction motors. The quantities which are considered as variables are the turns per coil, the wire diameter and the stack length. The method is considered initially in the context of a typical specification for small induction motors, but the effect of the inclusion of additonal items in the specification is also discussed. The material cost and performance of several standard motors are compared with their optimised equivalents.

DOI:10.1049/piee.1976.0027

出版商:IEE    

年代:1976

数据来源: IET

摘要:

A frequently recurring problem in induction device theory involves the determination of the input wave impedance to a device. This is commonly done by solving for the field components. In this paper, a completely different method based on the scalar Riccati equation is described. It is shown that the wave impedance can be obtained by the numerical integration of a Riccati-type differential equation, having wave impedance as the unknown variable. This is illustrated with three simple models each having an unknown field distribution in one direction only. Extensive computer testing was carried out and the results obtained were found to agree very closely with published analytical methods. The method is very simple, easily programmed and avoids the use of higher transcendental functions.

DOI:10.1049/piee.1976.0028

出版商:IEE    

年代:1976

数据来源: IET

DOI:10.1049/piee.1976.0029

出版商:IEE    

年代:1976

数据来源: IET

摘要:

A method is given for obtaining the equivalent circuit of a set of concentric circular cylindrical conducting tubes within an alternating axial magnetic field. First, a general form of field solution is obtained using transfer matrices. A variable transformation is then made which makes it possible to derive an equivalent circuit for each annular region in the device. By joining the equivalent circuits in cascade, an equivalent circuit for the complete device is obtained. The applications of the theory include: electromagnetic shielding, flaw detectors and eddy-current heating. By using an equivalent circuit instead of the analytical form of field solution, much effort can be saved in both analysis and calculation. Experimental results are shown for shielding and impedance measurement.

DOI:10.1049/piee.1976.0030

出版商:IEE    

年代:1976

数据来源: IET

摘要:

The paper examines the effect of residual flux on switching transients in single-phase and 3-phase transformers, both experimentally and by calculation. Ferroresonance in single-phase and 3-phase transformers is also studied, with particular reference to the various modes, e.g. subharmonic. The basic equations for the transformer have been extended to include the effects of capacitance. The external circuit model used corresponds to a simple representation of capacitively-coupled transmission lines. Experimental and computed results are presented.

DOI:10.1049/piee.1976.0031

出版商:IEE    

年代:1976

数据来源: IET