摘要:

The first part of this paper deals with the selection, calibration, maintenance and operation of apparatus standards selected as representative samples of the types of telephones in general use. Particulars of the acoustical and electrical characteristics of microphones and receivers are given.The second part of the paper deals with telephone standards giving high-quality transmission and specially designed for standardization purposes, and of which the acoustical and electrical characteristics are capable of precise specification and measurement.The Appendix deals with the range of frequencies required for various classes of telephonic transmission.

DOI:10.1049/jiee-1.1928.0008

出版商:IEE    

年代:1928

数据来源: IET

摘要:

A description is given of a series of experiments to determine the attenuation of wireless waves over land. The intensity of the signals from the London broadcasting station (2 LO; λ = 364 m) was measured along a number of radial lines in seven different directions up to a maximum distance of 100 miles. From these measurements curves were drawn of the overall attenuation, and derived curves showing only the surface absorption effect. The experimental results were then compared with curves drawn in accordance with Sommerfeld's theory of attenuation. The results show that the attenuation is not the same in all directions, the difference being quite important, and the comparison with theory shows for all directions a considerably greater attenuation than would be expected from the previously determined value of the earth's conductivity.It is suggested that both these features of the results could be explained as an effect due largely to the well-wooded nature of the English country-side. To show this, an experimental method was developed by which the energy-absorbing property of individual trees could be directly measured. The results obtained enabled the total energy-absorbing properties of a given tree-covered area to be calculated, thus providing a correction for trees which could be introduced into the theoretical formula.The conclusion arrived at was that the greater part of the discrepancy between Sommerfeld's theory and experiment could be ascribed to the effect of trees, and also that the same agency offered a satisfactory explanation of the difference of attenuation observed in different directions—the greatest attenuation corresponding to the most-wooded regions, and vice versa.The experimental results show no evidence of any screening or other effect due to hill systems encountered in the region investigated, which included the North and South Downs and the Chiltern and Cotswold ranges.Finally, check-measurements of attenuation on two other wave-lengths gave results satisfactorily confirming the conclusion derived from the main experiments.

DOI:10.1049/jiee-1.1928.0012

出版商:IEE    

年代:1928

数据来源: IET

摘要:

It is known that the value of the power factor of a balanced three-phase load obtained by the two-wattmeter and the three-wattmeter methods are not always the same. It is known also that the ratio of the mesh voltage to the star voltage to earth is not always equal to √3. The author investigates the reasons for these variations and with the help of solid geometry develops a pictorial method of considering the problem. It is proved that √3 is the maximum value of the ratio of the mesh voltage to the potential difference between a terminal and earth. It is also proved that a star inductive load only has an equivalent mesh load when the time constants of the arms of the star load are all equal.

DOI:10.1049/jiee-1.1928.0014

出版商:IEE    

年代:1928

数据来源: IET

摘要:

The author was led to write this paper by reading Mr. F. Creedy's paper entitled “Some Developments in Multi-Speed Cascade Induction Motors,” † and the present paper mainly shows a new way of arriving at the same conclusions as Mr. Creedy.For the sake of clearness the new method of studying the subject is first applied to the ordinary windings which produce only one rotary field. The two-field windings on the rotor of the cascade motor are then treated, and finally some curves are given showing the amount of copper used in the cascade windings, compared with that employed in the ordinary windings.

DOI:10.1049/jiee-1.1928.0015

出版商:IEE    

年代:1928

数据来源: IET