摘要:

It is proposed to outline the activities of the Post Office in telecommunication research. It is not proposed, however, within the limits of this paper to deal with radio work. Description of the Dollis Hill Research Station with regard to the lay-out, buildings, and organization, is followed by details of the various research groups. So far as possible, the paper is confined to descriptions of principles and methods involved in carrying out the various types of investigations, and, in general, details of individual researches are omitted. In a few specific cases, however, it has been considered desirable to give certain details in order to convey some indication of what is involved in telecommunication research. The paper deals primarily with the period since the establishment in 1921 of the Dollis Hill Research Station. In order, however, to complete the picture, it is desirable in the first place to refer briefly to the period prior to 1921.

DOI:10.1049/jiee-1.1934.0111

出版商:IEE    

年代:1934

数据来源: IET

摘要:

The paper first deals with the evolution of the Benson boiler and then proceeds to detail the steps taken to enable it to be used for commercial purposes, first at critical and later at sub-critical pressures.The present design of the boiler is next discussed and it is claimed that a considerable saving in weight and cost is obtained with it as compared with ordinary water-tube boilers. A brief discussion of the probable future development of the boiler follows.The operation of the boiler at variable pressure is next dealt with. Finally, some figures of cost are given and the advantages and possibilities of the boiler are summarized.

DOI:10.1049/jiee-1.1934.0116

出版商:IEE    

年代:1934

数据来源: IET

摘要:

The paper discusses the problems of summation metering arising from the requirements of the 1926 Act, and it indicates the reasons which led to the choice of impulse instead of electrical summation on the larger equipments. For duplicate circuits the latter has been adopted as being simpler and less expensive. The types of meters installed were specially designed for grid metering purposes, and the accuracy obtained is an advance on previous requirements.The methods of impulse transmission and reception are described and compared, and it is shown that for uniform accuracy and performance “graded” impulsing is essential. The rate of impulsing has a decided effect on the life of the equipment and also on its accuracy. Considerable experience has already been gained in several of the grid districts, and the modifications which have been made to weak designs have resulted in consistent and accurate records.The large financial transactions dependent on the metering records make exacting demands on the equipments, and the number of operations performed annually necessitates constant and regular maintenance, for which a suitable programme is suggested.The number of faults to be expected on a satisfactory equipment is indicated, and it is shown that, although the majority of these are of a minor nature, delay in drawing up fault reports may result in the records being lost at a critical period.

DOI:10.1049/jiee-1.1934.0121

出版商:IEE    

年代:1934

数据来源: IET

摘要:

The paper gives an account of some measurements of ground electrical constantskand Σ made by the tilting-rod apparatus, being a continuation, on shorter waves, of the experiments described in an earlier paper. The employment of higher frequencies involved some modification of the apparatus and also an extension of the theory to allow for the effect of the dielectric constant, which begins to influence the results under these circumstances. The paper divides the measurements into four groups: (1)Measurements made at one site over prolonged periods to investigate seasonal variation. (2)Measurements on selected sites over a large range of wavelengths to determinekand Σ. (3) Summary of all measurements made at a number of different sites to determine Σ only. (4) Measurements made on sites with abnormal ground surface, singled out in a separate table for the purpose of emphasis and comment.A theoretical section is devoted to the extension of the analysis of the field of a plane wave advancing over the surface of an imperfect conductor, in order to derive a simple relationship between wavelength, tilt angle, conductivity, and dielectric constant. Values of Σ andk,are obtained by plotting a suitable function of tilt angle against frequency and choosing from a series of theoretical curves, plotted for different values of Σ andkthat which most nearly fits the results. It is concluded that no seasonal change of Σ was detectable, but that changes from wet to dry weather had an appreciable effect and that the conductivity was not appreciably different from its long-wave value. The series of measurements taken on a large area of ice over deep fresh water probably constitute the most interesting results, giving values of 100 forkand 1.4 × 108for Σ. Theory indicates that the results may be regarded as applying to the water rather than to the ice. This is confirmed by the value ofkobtained, which corresponds approximately to the normal “static” value of the dielectric constant of water and is many times greater than that of ice.

DOI:10.1049/jiee-1.1934.0126

出版商:IEE    

年代:1934

数据来源: IET

摘要:

The electrical properties of the earth play an important part in many modern applications of physics and electrical engineering. In the early portion of this paper a summary is given of the published information on the electrical properties of soil for alternating currents at frequencies from 50 to nearly 200 million cycles per sec. Particular interest is attached to the properties at radio frequencies, and it is shown that, while a certain amount of knowledge has been acquired by the use of field methods depending upon some characteristic of electric wave propagation, the results available apply to certain rather scattered ranges of frequencies and to some fairly localized portions of the earth's surface.The later portions of the paper are concerned with the investigation of the conductivity and dielectric constant of samples of soil by a laboratory method of measuring resistance and reactance at radio frequencies. This method was used for the majority of the measurements which were carried out at frequencies between 100 and 10 000 kilocycles per sec., but, by the aid of a standard type of capacitance bridge, the work was extended through the audio-frequency range to a power frequency of 50 cycles per sec.A series of preliminary measurements showed that reliable results could be obtained which were independent of the size and shape of the fixed condenser, in which the soil was packed as the dielectric. The conductivity and dielectric constant were both found to be very dependent upon the moisture content of the soil, except when this was within the normal range for the site under consideration. In a typical case the conductivity for dry soil, at a frequency of 1 200 kilocycles per sec., was of the order of 105electrostatic units (corresponding to a resistivity of 9 megohms per cm cube), while at a moisture content of between 12 and 26 per cent a limiting value of between 108and 2 × 108electrostatic units (resistivity 9 000 to 4 500 ohms per cm cube) was obtained. The corresponding values of dielectric constant ranged from 3 or 4 for dry soil up to 30 or 40 for very moist soil. The effect of frequency on conductivity was more marked for dry than for moist soil, and in the latter case there was a small although definite rise in the conductivity at the highest frequencies. The dielectric constant decreased with increase of frequency towards a limiting value for moist soil, whereas for dry soil the variation of dielectric constant with frequency was very small. From measurements made on samples of different types of soil it was found that the temperature coefficient of the conductivity at 20°C. was about 2.3 per cent per deg. C., whereas the effect of temperature on the dielectric constant was negligible. In both cases, however, a sudden decrease in the value took place in passing through O° C., which is attributable to the partial or total freezing of the water content.When the validity of the laboratory method had been established, and it had been found that the results obtained thereby agreed with those previously available from field measurements, the investigation was extended to a study of the properties of soil from 12 different sites in England and Scotland. In the majority of these cases, samples of soil were obtained for measurement at various depths down to 10 ft., while in one case the depth was extended to 300 ft. The results are given in detail in tabular form in the paper. It is shown that, at a typical frequency of 1 200 kilocycles per sec., the conductivity of surface soil varies between 0.16 × 108and 4.0 × 108electrostatic units for different sites, while at various depths the values range from 1.6 × 105to about 1010electrostatic units. In general it is shown that the clay soils have a high conductivity (i.e. above 108electrostatic units) accompanied by high dielectric constant, and the loam and chalk soils an average value of about 108electrostatic units for conductivity and 20 for dielectric constant, while soil of a sandy or gritty nature gives a much lower conductivity value. The lowest values (of the order of 105electrostatic units) mentioned above were obtained on the solid granite or slate subsoils found at some of the sites.The concluding section of the paper illustrates in graphical form the effect of the electrical properties of the soil on the penetration of alternating currents below the surface. Curves are plotted for certain of the sites from which samples of soil were obtained for measurement. These curves illustrate the fact that while at a frequency of 100 kilocycles per sec. a few per cent of the current at the surface may penetrate to a depth of 20 metres (over 60 ft.), at a frequency of 10 000 kilocycles per sec. the current is practically confined to the first 3 or 4 metres of depth. The effect of such current penetration on the field at the surface due to an electric wave being propagated along this surface is a subject that must remain for further investigation.

DOI:10.1049/jiee-1.1934.0127

出版商:IEE    

年代:1934

数据来源: IET

摘要:

The paper gives an account of the development and construction of the new transmitter now installed at the National Physical Laboratory for the emission of the special signals required in connection with modern research on the ionosphere. It also deals briefly with the methods adopted for the dissemination of standard-frequency signals for calibration purposes.The new installation has been designed to handle all the sending services required from the Laboratory over a continuous frequency range of 250 to 6000 kilocycles per sec.(wavelength 1200 to 50 metres). Owing to the rapid change in the emitted frequency required in many tests, a single oscillating circuit is employed and the oscillations are maintained by a push-pull system. A series modulator is provided for controlling the anode-circuit supply to the oscillator. The special emissions required for ionospheric research consist of frequency-change and pulse transmissions. In the former emission, the frequency is continuously varied over a small range by means of an entirely automatic mechanism which gives precision of both timing and frequency-change, while in the latter type of emission, pulses of waves may be emitted of short duration and at a repetition frequency synchronized with the a.c. supply mains.Two types of standard-frequency programmes are emitted. In one of these the output from the continuously-running 1000-cycle standard tuning-fork is used to modulate a suitable carrier wave; and in the other a standard radio frequency is emitted by using the transmitter as the final stage in an amplifier supplied by a quartz-crystal-controlled master oscillator.All the operations required in connection with these various emissions are effected by simple panel switchgear so as to render rapid changes in frequency and type of transmission possible, while a cathode-ray oscillograph equipment is incorporated for the observation of the modulation envelope.The whole installation was designed and constructed at the Laboratory for an input power of at least 4kW, although at present the input is limited by supply conditions to 2kW.

DOI:10.1049/jiee-1.1934.0129

出版商:IEE    

年代:1934

数据来源: IET