摘要:

Assuming that current-density/electric-field curves are provided and that the Hall mobility does not change appreciably with the electric field, the small-signal tensor conductivity of n-GaAs in the presence of d.c. electric and magnetic fields is derived. Using this tensor conductivity, carrier-wave equations are solved for a long slab of n-GaAs sandwiched between dielectrics. It is found that wave vectors are generally skewed against the direction of the direct current. The gain factor of the propagation coefficient is found to be controllable by the magnetic field, especially when the slab is thin and the d.c. electric field is near the threshold value.

DOI:10.1049/piee.1972.0109

出版商:IEE    

年代:1972

数据来源: IET

摘要:

The paper reports on an investigation of the application of variable-level quantisation in p.c.m.-type speech-transmission systems. Variable-level (dithered) quantisation systems are compared with normal fixed-level quantisation systems. The systems are compared using intelligibility tests and subjective-appreciation tests, and a statistical analysis of the results is given. The analysis indicates that, in general, normal quantisation is superior to dithered quantisation.

DOI:10.1049/piee.1972.0110

出版商:IEE    

年代:1972

数据来源: IET

摘要:

Numerical results for elliptical waveguides are usually obtained from the appropriate Mathieu and associated Mathieu functions, but these are expensive to compute, because of slow convergence, and difficult to tabulate. It is shown that results for the cutoff wavelengths can be obtained using simple new formulas relating the ellipse (or circle) to an inscribed polygon. Cutoff wavelengths for the polygon can then be obtained efficiently using an available computer program. In this way, by applying boundary perturbation theory, the accuracy for cutoff wavelength from the original program has been increased by a factor of up to 104. Besides using an extrapolation technique, special advantage is taken of the elliptical shape which allows an ‘area correction’ to be applied to the approximating polygonal results.

DOI:10.1049/piee.1972.0111

出版商:IEE    

年代:1972

数据来源: IET

摘要:

A study of the complete mode spectrum of the dielectric-tube-loaded coaxial cable reveals that only the low-loss slow-wave TM01mode has no lower cutoff frequency. Mode designations are shown to be consistent with those previously adopted for dielectric waveguides. A numerical optimisation procedure is applied to an accurate perturbation analysis of the dominant mode to determine optimum dielectric-tube radial dimensions for minimum loss. Attenuation reductions as high as 75% of the unloaded values are attainable in certain overmoded cases. For the optimum conditions, the cable is well equalised, and the propagation characteristics are relatively insensitive to small variations in the dimensions of the tube.

DOI:10.1049/piee.1972.0112

出版商:IEE    

年代:1972

数据来源: IET

摘要:

A 1/30th scale model of the international standard instrument-landing-system glidepath is described. Interference effects on the linearity of the path in space are investigated, and a theoretical analysis is applied which confirms the integrity of the model operation. The effects due to aircraft taxying in typical airport regions have been measured using accurate scale models of common civil aircraft. Typical results are presented.

DOI:10.1049/piee.1972.0113

出版商:IEE    

年代:1972

数据来源: IET

摘要:

By using the results on explicit formulas for element values in 1-variable ladder networks dependent on one or two auxiliary parameters, and by using appropriate frequency transformations, certain generalisations may be made to 2-variable networks. For the solution to the approximation problem, which results in an elliptic function or Cheby̅shev response, nonreciprocal 2-variable networks result, but for the matched inverse-Cheby̅shev-response case, a simple 2-variable ladder network is obtained. This case is treated in detail, and typical responses for networks containing lumped and commensurate distributed elements are presented, with a specific example on a waveguide bandstop filter.

DOI:10.1049/piee.1972.0114

出版商:IEE    

年代:1972

数据来源: IET

摘要:

A development in laboratory bench-testing facilities for protective schemes is described. Test benches used at present contain linear inductors which have high X/R ratios so that offset transients associated with power systems may be simulated. However, owing to losses in the test network, these transients cannot be satisfactorily reproduced at large currents. It is shown here that by replacing the make switch in the conventional test bench with two inverse-parallel-connected thyristors, fired at carefully chosen intervals, it is possible to simulate transients on any system with acceptable accuracy. Details of the proposed test circuits are given, and both computed and experimentally obtained results are included to illustrate the negligible nature of the errors introduced. A method using the equipment for fusegear testing is also described.

DOI:10.1049/piee.1972.0115

出版商:IEE    

年代:1972

数据来源: IET

摘要:

A system is described for the measurement of the phase angle between two voltages separated from each other, and from the point where the results are to be displayed, by a distance of several miles. A correction for the transmission delay of the measurement signals is automatically made, and an accurate knowledge of the transmission-path characteristics is not required. At power frequencies, the measurement accuracy is within a small fraction of one degree.

DOI:10.1049/piee.1972.0118

出版商:IEE    

年代:1972

数据来源: IET

摘要:

Reactive-power installations at suitable points become necessary in most modern high-voltage networks, to prevent excessive voltage drops at load busbars. In the paper, the minimisation of the total required reactive-power installation is formulated as a nonlinear-programming problem. Based on certain specific features of this problem, a new solution technique, which results in a considerable reduction of computational effort, as compared with general optimisation techniques, is developed. An additional feature of this technique is that it can be used in conjunction with any standard a.c. load-flow program. The technique is applied to a typical network to bring out the advantages of this approach. An extension of this technique for cases where the voltage restrictions have to be satisfied for two or more loading conditions is also presented.

DOI:10.1049/piee.1972.0119

出版商:IEE    

年代:1972

数据来源: IET

摘要:

The simplest way of improving protective-current-transformer performance during transients is to make the transformer's magnetising inductance relatively low. This method may diminish transient errors but always increases steady-state errors. If the maximum acceptable transient error is defined, the primary current that may be transformed during the transient within the error limits depends on the transformer's magnetising inductance. For certain values of the magnetising inductance, this current reaches its maximum. It enables an optimisation of the protective current transformer to be made by adjusting both the core cross-section and the airgap length to achieve the desired level of transient accuracy.

DOI:10.1049/piee.1972.0120

出版商:IEE    

年代:1972

数据来源: IET