摘要:

A programme channel requires greater bandwidth than a normal telephone speech channel. It can be accommodated in a time-division multiplex (t.d.m.) transmission system by using the pulse trains of several speech channels. The paper shows that, when these pulse trains are not equally spaced, distortion components are produced in the output signal.In general, the distortion components are at the channel pulse-repetition frequency and its harmonics, together with upper and lower sideband components. To obtain a sufficiently low distortion level, the permissible departures from equal pulse spacing are only of the order of ±1° or less. Similar distortion is also introduced if the pulses are not identical in height and shape. To obtain sufficiently low distortion level, the differences in height and length of the pulses used for a programme channel may only be of the order of 1%.Although the analysis is made for t.d.m. systems using pulse-amplitude modulation (p.a.m.), its results are shown to be applicable to some systems using other forms of modulation, such as pulse-code modulation (p.c.m.). It is concluded that p.c.m. systems are unsuitable for programme transmission unless the total number of time slots per frame (including synchronising pulses) is an exact multiple of the number of speech channels required to constitute a programme channel.

DOI:10.1049/piee.1965.0241

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The relations between the field distribution across an aperture, its autocorrelation function and the angular power spectrum of the radiated field are used to analyse the fields produced by particular aperture distributions. The effect of illuminating only a small part of the total area of a large aperture is considered, and some of the average properties resulting from a randomly distributed illumination are derived. The case of linear arrays with a statistically small number of elements is also considered. The method outlined may also be extended to cylindrical or spherical arrays.

DOI:10.1049/piee.1965.0242

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The characteristics of the surface waves guided along a perfectly conducting infinite cylinder are investigated for the case in which it is immersed in a magnetoionic medium and oriented so that its axis is parallel to the direction of the magnetostatic field. The surface waves are found to be propagated along the cylinder for frequencies less than the plasma or the gyromagnetic frequency of the electrons, whichever is lower. The phase velocity of the surface waves is always less than the velocity of electromagnetic waves in free space. The dependence of the characteristics of the surface waves on the radius of the cylinder is also examined.

DOI:10.1049/piee.1965.0243

出版商:IEE    

年代:1965

数据来源: IET

摘要:

Heater/cathode insulation in indirectly heated valves is considered as a two-part phenomenon: the comparatively slow deterioration during operational conditions followed by a rapid thermal breakdown, which is caused directly by the sudden passage of a large current between heater and cathode.Examination of heater/cathode failures in valves tested under rigidly controlled conditions has indicated some of the laws governing the deterioration of the insulation. The effects of various parameters such as temperature of operation, thickness of insulation and applied potential have been studied, and comparisons have also been made for different heater and cathode materials.The experimental evidence is discussed in an attempt to explain the failure mechanism involved, and the conclusion that electrolysis is the principal factor is supported by the results of a number of experiments carried out with specially designed electrode structures.

DOI:10.1049/piee.1965.0244

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The Linvill models and the more conventional equivalent circuits can be used to make roughly equally accurate predictions of terminal behaviour of semiconductor devices. An extreme case, the diode storage time, illustrates this point. The principal feature of the Linvill models, not found in other models, is that current is expressed in terms of excess hole and electron densities. Specifically, the distributed current in a semiconductor device is approximated in the Linvill model by a finite number of currents in corresponding current nodes, and each of the nodes is associated with a particular elementary volume. The relation between the hole- and electron-charge density and the current in any elementary volume is represented by elements of a lumped equivalent circuit.When the models are applied to a practical problem, it is not possible to use the very large number of lumped elements which would be needed closely to model the distributed current, and a small number of model elements is used. In such a ‘simplified’ model, the one-to-one correspondence between model space and device space is obscure, and, furthermore, conditions based on this correspondence are not sufficient to obtain correctly the model element values. Using, in the last analysis, arbitrary configurations, the model elements must be calculated in such a manner that they match some set of terminal characteristics. A further practical drawback is that the lumped elements cannot be measured directly because they are expressible in terms of hole and electron concentrations, themselves not measurable.Without altering the intent of the Linvill approach, both of the above difficulties can be mitigated. One can represent the currents in the device by an alternative set of lumped elements in which the notion of volume is absent. Such elements are not necessarily associated with physical volumes and no contradictions are encountered with the simplified models. The alternative set of elements proposed in this paper can, furthermore, often be measured in terms of current and voltage. A last by no means negligible advantage is that a special symbolism is not required.

DOI:10.1049/piee.1965.0245

出版商:IEE    

年代:1965

数据来源: IET

摘要:

A large-signal analysis of varactor harmonic generators without idlers is given. The voltage across the varactor is expressed as a Fourier series in the harmonic charges, and, by expressing the input circuit as an impedance, and the output circuit as a voltage generator in series with an impedance, the relevant coefficients of the series are found. It is found expedient to express the circuit in this way in order to determine the coefficients without any approximation. The efficiency is then calculated as a function of input power; it is found that, for maximum efficiency, input and output resistances should be equal and an expression is given to determine their value. Finally, design curves are given for second-, third- and fourth-harmonic generators, from which optimum operating conditions can be found.

DOI:10.1049/piee.1965.0246

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The paper describes a new type of electronic analogue multiplier-divider, in which a voltage-controlled variable-gain element, based on the field-effect transistor, is shared in time between two circuits. In one circuit, the gain is made proportional to the ratio of two input signals; in the other, it acts on a third input signal to provide the output.Sharing is effected at, for example, a frequency of 1 kc/s, by transistor switches, and the system performs 4-quadrant multiplication and 1-quadrant division. Only one, simple a.c., amplifier is required, and high accuracy can be achieved with input signals having full-scale values as low as 5V and 10μA.

DOI:10.1049/piee.1965.0247

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The brushes in d.c. machines bridge the micas between the commutator segments, and the coils thereby short-circuited may carry parasitic currents. As described in a previous paper on d.c. generators, the short-circuited loops may be represented, for many calculations, by an auxiliary-armature circuit. In the present paper, it is shown, by calculation and test, that the parasitic currents may have marked effects on the speed-regulation properties of motors under linear conditions, and that these effects may partly persist in the nonlinear régime. It is suggested that many anomalies, commonly ascribed in an undefined way to brush effects and armature reaction, are amenable to a stricter treatment in terms of the concepts proposed.

DOI:10.1049/piee.1965.0250

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The paper describes experimental results obtained from transient tests on a laboratory universal machine, connected to operate as a 3-phase alternator. During these tests, which were carried out in order to measure the parameters, severe harmonic distortion was found in the armature-current waveform under conditions of sudden symmetrical short circuit. This appeared to be mainly second and third harmonic together with a very low-frequency subharmonic. The paper gives an analysis of the machine with computed values of transient current and shows that, with the compromise design used to achieve a measure of generalisation, such harmonics are to be expected. It also shows mathematically that the usual transient d.c. component in the armature current may become a transient, very-low-frequency oscillation, depending on the machine parameters.These effects observed on a ‘universal machine’ were also found during tests carried out on a second generalised machine of different design.It was found that damping and field time constant have considerable effect on the transient harmonic distortion in the short-circuit armature current.

DOI:10.1049/piee.1965.0252

出版商:IEE    

年代:1965

数据来源: IET

摘要:

Single-step methods of numerical integration, such as the Runge-Kutta routine, have been widely used in the application of digital computers to the analysis of transient stability in synchronous power systems, but no previous paper appears to have described the alternative integration methods, which are based on prediction and correction, although they are being increasingly used in other scientific applications of digital computers. The purpose of the present account is therefore to document a comprehensive series of experiments which incorporate several different predictor-corrector methods, the primary aim of which has been to discover the feasibility of using longer step lengths than are possible with single-step methods, thereby reducing the total computing time expended in analysis.The experiments indicate that the length of step interval is influenced, in addition to the precise technique of integration, by the essential basis of step-by-step analysis, in which the solutions of algebraic equations always lie one step behind those of differential equations. A method of auxiliary prediction of nonintegrable variables is developed to promote a closer realisation of their required simultaneous solution, and the substantial increase in step length which then becomes possible is demonstrated.

DOI:10.1049/piee.1965.0253

出版商:IEE    

年代:1965

数据来源: IET