摘要:

A description is given of results obtained from soundings made with a spaced-cavity balloon-borne refractometer and 10cm-band vertical-incidence radar. The experiments, carried out at Cardington, Beds., England, in 1964 and 1965, show that at heights up to 2km there is often considerable inhomogeneity in the refractive-index structure, even in nonanticyclonic conditions. Instantaneous differences in refractive index of 5 parts in 106(5N units) were observed over distances of 11cm within discrete parcels of air in which the quotient of variance by scale size was unusually large, occasionally 10−11m−1. Such parcels were often located at or near the base of a layer of steep mean vertical gradient in refractive index associated with elevated inversions or isothermals. The results are discussed in relation to meteorological factors, such as wind shear and dynamic stability, and to theories of tropospheric scatter based on the concept of homogeneous turbulence.

DOI:10.1049/piee.1968.0217

出版商:IEE    

年代:1968

数据来源: IET

摘要:

Spatial (wave-number) spectra of refractive-index variations have been derived from measurements of frequency spectra made with a spaced-cavity refractometer located in and near elevated inversion layers. The intensity of the 1-dimensional wave-number spectrum decreased with increasing wave numberkask−n, with values ofngenerally greater than 5/3 and occasionally as large as 3 [kmay be regarded as equal to 2π/(blob size)]. The largest values ofnwere usually found in layers across which the value of Richardson's number was appreciably greater than unity. The variation from sample to sample in any sounding in the spectra intensity atk∽ 100m−1was often appreciably less than the corresponding variation atk∽ 1m−1. The results illustrate the dependence of spectral characteristics on sampling time.

DOI:10.1049/piee.1968.0218

出版商:IEE    

年代:1968

数据来源: IET

摘要:

A Taylor-series expansion is applied in the complex frequency plane in order to find the admittance of an antenna in a dissipative medium from the admittance of the same antenna in air. The admittance of a dipole antenna immersed in mediums with tan δ = 0.01 and 0.02 is tabulated. The values so obtained are in good agreement with measurements. The error and the range of values of the loss tangent of the medium, and the length of the antenna for which the present method is applicable, are examined from various points of view.

DOI:10.1049/piee.1968.0219

出版商:IEE    

年代:1968

数据来源: IET

摘要:

Public telecommunication networks are required to transmit various types of information, and any new method of transmission must provide a quality at least as good as the present standards. This paper describes the basis on which the fundamental characteristics were chosen for the new 24-channel short-distance p.c.m. system now being introduced by the British Post Office.Representative overall telephone connections were selected and assessments made of their speech-transmission performance when certain links in them are provided by p.c.m. systems having various sets of fundamental characteristics. Special attention was given to requirements concerning load capacity, quantising distortion (including performance at very low signal levels) and circuit noise. Acceptable values for each quantity were determined and certain compression characteristics examined in the light of these requirementsThe final choice of fundamental characteristics was based mainly on consideration of speech, and the new systems should provide a suitable standard for any conditions of use for telephony that can be envisaged at present. It is believed that other services that the systems may be required to transmit impose less onerous conditions than those for speech, and so it is expected that they will also satisfy requirements for these other services.

DOI:10.1049/piee.1968.0220

出版商:IEE    

年代:1968

数据来源: IET

摘要:

The upper bound on the order of complexity σmaxof general linear active networks is found. The result thus completes those already obtained for theRLCnetworks and for a restricted class of active networks.The result is applicable to networks consisting of independent sources, resistors, capacitors, inductors, gyrators, multiwinding ideal transformers and the four types of controlled sources. The voltage graph (NV) and the current graph (NI) associated with the active network (N) are used in the derivation. A common tree is defined as a set of branches which forms a tree in bothNVandNI. The network ‘operator matrix’ includes the set of equations resulting from Kirchhoff's voltage and current laws, applied toNVandNI, respectively, and the element behaviour between the corresponding branches inNVandNI.The order of complexity is obtained by an expansion of the determinant of the operator matrix and can be stated with respect to some particular common trees.In the state-space (variable) approach to network synthesis, the order of complexity represents the minimum number of reactive elements required for the realisation

DOI:10.1049/piee.1968.0221

出版商:IEE    

年代:1968

数据来源: IET

摘要:

The modified cut-set matrix of ann-port network is defined and its properties are enumerated. The importance of this concept in considering the parallel interconnection ofn-port networks containingR,LandCelements is demonstrated. A procedure is obtained for the generation of a class of continuously equivalent networks of a givenRLCn-port network. The class is characterised by the property that all networks belonging to this class have the same modified cut-set matrix. Using this procedure, it can be shown that, for a resistiven-port network in which every pair of vertexes is connected by a finite positive conductance, a large number of continuously equivalent networks containing only nonnegative conductances can always be obtained. The usefulness of this result in the synthesis ofRLCn-port networks is indicated

DOI:10.1049/piee.1968.0222

出版商:IEE    

年代:1968

数据来源: IET

摘要:

A procedure for the realisation of a generalKnetwork, which is a generalisation of the conventional 2n-node network realisation of a dominant matrix, is given. It is shown that a set of dominant matrices can be realised by 2n-noden-port networks having the same modified cut-set matrix. This technique is used in evolving a procedure for the realisation of 2-element-kindn-port networks.

DOI:10.1049/piee.1968.0223

出版商:IEE    

年代:1968

数据来源: IET

摘要:

Every electrical machine consists of electric and magnetic circuits interlinked. Good machines have circuits of low resistance and reluctance, the latter generally achieved by the use of a steel structure. If magnetic flux is made to thread a relatively long air path, compensation for the higher reluctance otherwise introduced can be sought by making the area of the flux path large.The paper shows how useful shapes of machine can be developed in which a large part or all of the magnetic circuit consists of air. Machines included are open-bar transformers, single-sided linear induction motors, and homopolar d.c. machines with superconducting field windings. Vertical forces in open-sided linear motors are calculated.The paper concludes with a brief discussion of the possibilities of electromagnetic current collection for traction systems employing a moving transformer

DOI:10.1049/piee.1968.0224

出版商:IEE    

年代:1968

数据来源: IET

摘要:

The Graetz (3-phase) bridge circuit is the arrangement usually chosen for a 3-phase d.c. convertor, because it has the best valve and transformer utilisation, and hence lowest valve costs. This bridge has the disadvantage that the alternating current is fixed relative to the direct current, which means that the reactive-power requirement is dependent upon the active power. If three single-phase bridge circuits are used, however, it is possible to vary the relationship between the alternating and the direct currents, and hence it is possible to change reactive power without varying active power. This facility is particularly useful when a number of convertors are connected in series on the d.c. side, when the direct current is common to all convertors and voltage control is used to set the active power level. The operation of a convertor using three single-phase bridge circuits is analysed, and it is shown that, although the bridge is more expensive on valves, it has operational advantages over the conventional Graetz bridge. The theoretical and practical operating limitations are discussed, and it is shown that the convertor can be operated continuously over its complete power range with a reactive-power requirement of only 70% of the rated convertor apparent power, compared with 100% for a Graetz bridge. The cost of terminal plant other than valves is shown to be the same for both convertor circuits. In a brief economic assessment, it is shown that the overall cost of the new convertor may be only 14% higher than a similarly rated Graetz bridge

DOI:10.1049/piee.1968.0227

出版商:IEE    

年代:1968

数据来源: IET

摘要:

The current and potential along an extensive underground conductor are determined for voltage, current and conductive energisations. The general expressions for current and potential are derived, and it is shown that the approximate relations may be obtained from differential equations based on the equivalent circuit for the underground conductor. In the case of conductive energisation, the point, parallel and perpendicular earth electrodes are considered. it is shown that parallel or perpendicular earth electrodes, being sufficiently short, may be replaced by an equivalent point earth electrode

DOI:10.1049/piee.1968.0229

出版商:IEE    

年代:1968

数据来源: IET