DOI:10.1049/jiee-1.1929.0108

出版商:IEE    

年代:1929

数据来源: IET

摘要:

The work of previous authors on the subject of paper as a cable-insulating material is briefly reviewed. It is shown that, in the past, attention has been directed too exclusively to the fibre stock, and the relation of the physical structure to the electrical properties has been relatively neglected. The characteristics which a cable-insulating paper should possess are then outlined. Briefly, these are high electric. strength, high oil-absorption, low electrical conductivity, high mechanical strength, and permanence.The results of tests designed to determine the relation of the paper structure to these qualities are then quoted and discussed. From these tests it is concluded that a satisfactory paper for power-cable insulation should have the fibres closely packed to give low bulk while still retaining high absorbency. The fibre packing should not be obtained by heavy surface calendering.The methods of test employed and the influence of the manufacturing processes on the product are briefly discussed in appendices.

DOI:10.1049/jiee-1.1929.0109

出版商:IEE    

年代:1929

数据来源: IET

摘要:

This paper is an account of work which was undertaken in the first place to study the performance under various conditions of paper-dielectric condensers such as are commonly used for power-factor correction.It shows that breakdown of dielectrics in service is due to ionization of entrapped air; and that, removal of the air being impossible, the design of cables and condensers should be such as to prevent ionization. The principle of this design is to subdivide the dielectric.The effect of surges in causing breakdown is indicated, and a new test for finished products is suggested.

DOI:10.1049/jiee-1.1929.0110

出版商:IEE    

年代:1929

数据来源: IET

摘要:

In this paper an account is given of investigations of shortwave transmission effects made during the past two years. These include, firstly an investigation of scattering, multiple signals and signal mutilation, which supplies perhaps the main bulk of the paper, secondly the results of a nine months' direction-finding interception of short-wave commercial stations, and finally a discussion, in the light of these results, of the problems of short-wave transmission and such cognate subjects as the nature and constitution of the Heaviside layer, fading and polarization effects.An opportunity is afforded for the revision of conclusions arrived at in the author's previous paper.* The chief alteration is in the estimated height of the lowest levels of the Heaviside layer in daytime. The accumulation of evidence from the time-lag experiments of Breit and Tuve, and the interference experiments of Appleton and those of Hollingworth (which incidentally both give the group time and consequently an over-estimate of the height) have led the author to a revision of the mathematical result by which he obtained from long-wave measurement the effective height of the daylight ionized layer, and in doing so he has found an error which makes the estimated height just double that previously obtained, for inseatd of the relationd0= h2/λ†we haved0= h2/λ, making the estimated height lie between 80 km for summer and 97 to 100 km for winter.Previously the value of τ, the mean time between collisions, was found to lie between the limits 0.5 × 10−6and 0.5 × 10−7(on the basis of magnetic storm effects). Calculations based on the kinetic theory would imply a height of between 76 and 92 km for these values of τ in fairly close agreement with the above, and there is no necessity to make the rather forced assumption previously made that the electronic mean free path was some 10 to 50 times greater than that calculated from the normal kinetic theory on the assumption that the electron may penetrate the outer rings of the molecules without being appreciably deflected. Apparently this effect occurs only in inert gases, such as helium, and is not likely to occur in the upper atmosphere.With regard to scattering, the glancing angle for transmission, great-circle bearings of the main rays, and the daylight attenuation, the author has found the previous conclusions to be on the whole well-founded.Some modification of the lower wave-length limit for night transmission is required, and the author finds that this lower limit depends on the time of the night and season. Late-night regions behave very differently from early-night regions, thus confirming Appleton's results showing a progressive change in the Heaviside layer during the hours of darkness. The short-wave daylight limit appears to be close to 10m, but sporadic long-distance transmissions have been observed on wave-lengths shorter than this.The interpretation of many observations of short-wave transmission depends upon a previous experimental knowledge of scattering. A discussion of scattering will therefore be given first, and later the general results of long-distance and short-distance direction -finding will be considered. Fading and magnetic storms will next be discussed, then “skip effects”, and finally a general theoretical discussion in the light of the results obtained will be given.

DOI:10.1049/jiee-1.1929.0114

出版商:IEE    

年代:1929

数据来源: IET

摘要:

This paper describes a high-frequency radio apparatus capable of measuring in absolute units the intensity of the electromagnetic field over the frequency band of 5 to 12 megacycles per sec. It is easily portable, since the total weight without batteries is only 60 lb. An untuned antenna, which is coupled to the grid of the detector valve in an unusual manner, is used to pick up the energy to be measured. Sensitivity is not seriously affected since the range of intensities which can be measured is from 10 microvolts per metre to 10 000 microvolts per metre. The screening difficulty is lessened by using a resistance attenuator and toroidal inductances, and by totally disconnecting the aerial during calibration. The set consists of a detector valve with which is associated a control valve. One stage of audio-frequency amplification follows the detector, and a diode used as a second detector allows a galvanometer to be used for the signal comparison. A separate heterodyne is used to obtain the audio frequency. A resistance method is used to attenuate the current from the local source. The complete apparatus has been subjected to a series of tests in self-consistency and absolute value, and these are described in the paper.

DOI:10.1049/jiee-1.1929.0116

出版商:IEE    

年代:1929

数据来源: IET

摘要:

A historical survey of the literature dealing with the reflection of wireless waves reveals a difference of opinion concerning the phase-change produced when reflection takes place from Hertzian rod oscillators.In this paper the currents produced in two tuned vertical aerials both acting as receivers in a radiation field are discussed theoretically. Two special cases are considered in detail, viz. (1). when the aerials are less than one wavelength apart and are in line with the transmitter("end-on" position), and (2) when they are less than one wave-length apart and at right angles to the transmitter ("broadside-on" position).In the first case, the current in the aeiral nearer to the transmitter attains a maximum value when the distanceDbetween the aerials is approximately 0.33λ or 0.85λ, and is a minimum whenDis approximately 0.60λ, where λ is the wave-length. The current in the aerial remote from the transmitter reaches a maximum value whenDis 0.16λ, and then steadily decreases as the distance between the aerials increases to one wave-length.For the "broadside-on" position, the current in each aerial attains a maximum when the distance between teh aerials in 0.71λ.The details of the design of the short-wave oscillator and receiving aerials are outlined, and the method of procedure in order to obtain the current measurements is described.The experimental results obtained are compared with the theoretical calculations. The solutions of the general equation tan a(1 + cos β) = (a2− 1)/a gives the critical values of the ratio of the distance between two tuned antennae to the length of the wave, for which the antenna currents are a maximum or a minimum, the plane of the antennae being at any angle β to the direction of propagation.

DOI:10.1049/jiee-1.1929.0118

出版商:IEE    

年代:1929

数据来源: IET