摘要:

Engineers differ from pure scientists in being concerned with products which have to be made. Manufacturing processes are therefore of vital importance to the electrical engineer, for they determine the practicability and economic possibilities of his designs. During the last ten years, manufacturing processes have begun to undergo fundamental changes, owing very largely to electronic developments. Numerical control will eventually alter our machine shops. Computers will handle all the vast quantity of paperwork, costing and accounting. Semiconductors are becoming of increasing importance, and the processes by which they are made are developing rapidly in sophistication. Electrical-engineering graduates who enter factory life, however, can make contributions in other areas than these, for, with the changes which are bound to come, the application of their intellectual approach to the multifarious problems they will meet can make a real contribution to our future. It is a contribution which the IEE should encourage.

DOI:10.1049/piee.1970.0001

出版商:IEE    

年代:1970

数据来源: IET

摘要:

Radio and the weather are intimately connected: from this stems the interdisciplinary subject of radio-meterorology. Out of the study of the effects of the weather on radio wave propagation, radio techniques for meterorological research and applications are evolved. Some consideration is given in the paper to the relationship between atmospheric electrical discharges (lightning) and associated radio phenomena, but the emphasis is mainly on the interaction between the troposphere, with its constituents, and very short radio waves. The importance of radiometerorological research to the development of space and terrestrial communication is discussed, and also the relevance of such research to a better appreciation of the dynamical processes in the lower atmosphere.

DOI:10.1049/piee.1970.0002

出版商:IEE    

年代:1970

数据来源: IET

摘要:

During the period from January to December 1966, measurements have been made of the mode structure and absorption loss for high-frequency (h.f.) transmissions received over oblique propagation paths ranging in length from 500 to 1000km. The propagation characteristics for these circuits have been evaluated for the conditions appropriate to the period of observation by means of a ray-tracing analysis developed from the Booker quartic equation and also by two ‘prediction’ methods. In general, the predicted values of absorption agree well with the experimental results, although some discrepancies occur during the winter months since neither of the prediction methods makes allowance for the anomalous winter behaviour. The accuracies of the ray-tracing results are dependent on the validity of the assumed ionospheric model, and, when electron-density/height distributions derived from vertical-incidence soundings at the receiving site are employed, the ray-tracing calculations of mode structure and absorption loss are found to be consistent with experimental observations of these parameters.

DOI:10.1049/piee.1970.0003

出版商:IEE    

年代:1970

数据来源: IET

摘要:

Signals received beyond the normal horizon by partial reflection at an elevated layer of large vertical gradient of refractive index have been calculated using a high-speed computer. The results, obtained for wavelengths between 1 and 30m and for transmitter-receiver spacings of 100–400km, are more extensive and accurate than those previously available. The received field strength is most sensitive to absolute changes in antenna height, is less sensitive to changes in layer height, and is least sensitive to absolute changes in transmitter-receiver spacing and the effective Earth radius.

DOI:10.1049/piee.1970.0004

出版商:IEE    

年代:1970

数据来源: IET

摘要:

A simple and quantitatively accurate representation of the current distribution in a dipole antenna immersed in a dissipative medium is derived. Numerical data are given and are found to be in good agreement with the experimental results when ∣kh∣≥ 1.0 and ∣Ka∣ ≤ 0.08.

DOI:10.1049/piee.1970.0005

出版商:IEE    

年代:1970

数据来源: IET

摘要:

A brief discussion of the theoretical approach to the problem of obtaining the maximum efficiency, for both paraboloidal- and spherical-reflector antennas, is presented. In both types of antenna, the problem reduces to obtaining the optimum combination of amplitude and phase of the hybrid modes propagating in the guide, so that, at the feed aperture, the resultant hybrid field closely matches that field which would be produced by a plane wave incident on the antenna. With shallow reflectors, a purely analytical method can be used, whereas graphical computer-aided optimisation techniques may be used to obtain the solution when the reflector is deep. The paper, however, presents a simple method of obtaining the approximate mode composition, which often proves to be satisfactory. As an illustration, results obtained by the approximate method are also compared with published results.

DOI:10.1049/piee.1970.0006

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The effects of mutual coupling and other errors on the directional performance of a zero-steering system for a linear array are considered. Some measured directional patterns, obtained from two different experimental systems employing 4-element-dipole arrays, are shown. The first model employs components of moderate accuracy, the second is a much more complex model are also shown. With a total of four dummy elements, the directional minima were between 20 and 50dB below the mainbeam response over a 180° sector in all measured patterns. Simplified systems for steering a restricted number of zeros, and the application of Zero-steering systems to planar arrays are also discussed.

DOI:10.1049/piee.1970.0007

出版商:IEE    

年代:1970

数据来源: IET

摘要:

It is found from experimental investigation that the equivalent network of a thin displaced longitudinal slot in the broad wall of a rectangular waveguide changes from a parallel element to a series element a back to parallel element again as the length of the slot is increased from about λ/2 to about 3λ/2. In the paper, analytical experssions for the immitance variations in the series and shunt forms of representations have deen found. The electric-field distribution in th aperture plance of the slot is replaced by suitable magnetic-curent distribution. The field distribution in the aperture plane of a slot, representable as a shunt element, is an even function and produces a discontinuity in modal current. The analytical expression for the complex admittance in the shunt form of equivalent network has been found from the reaction of the magnetic field due to the slot with the magnetic current exciting the slot and the discontinuity in modal current. A slot, whose equivalent network is a series element, has an odd distribution of electric field in its aperture plane, and such a slot produces a discontinuity in modal voltage. The analytical expression for the impedance in the series form of equivalent network is found from the power radiated by, and power stored in the vicinity of, the radiating slot and the discontinuity in modal voltage. The analytical expression for the impedance in the series form of equivalent network is found from the power radiated by, and power stored in the vicinity, of the radiating slot and the discontinuity in modal volage. The theoretical results are in good agreement with experimental observations.

DOI:10.1049/piee.1970.0008

出版商:IEE    

年代:1970

数据来源: IET

摘要:

A c.w.-burst signal is shown to have certain advantages over both pulse and normal c.w. techniques in the testing of coaxial cables intended for long-distance frequency-division-multiplex systems. The burst is made long enough to integrate the effect of reflections over a length of cable, yet sufficiently short to enable connector and termination reflections to be distinguished from those in the cable itself by means of an Ascan oscilloscope display. It is possible, in fact, to measure the v.s.w.r. of any segment of the cable by means of a suitable choice of burst length and observation time. An analysis is presented of the relationship between such a backscattered signal and the perturbation in the forward transmission with systematic irregularities of cable impedance. The effect of jointing practical drum lengths to form a repeater length of cable is discussed, and the analysis is illustrated by reference to the standard 9.5mm cable over the frequency range 10–100MHz.

DOI:10.1049/piee.1970.0009

出版商:IEE    

年代:1970

数据来源: IET

摘要:

Experimental measurements of the propagation characteristics of the basic OMEGA frequencies 10.2 and 13.6kHz, made in August 1966, taken over air routes within 2000km of the OMEGA Trinidad transmitter, are used to estimate errors in navigation due to the presence of more than one waveguide-propagation mode close to a transmitter. During the day, the maximum likely error due to propagation effects using the frequencies 10.2 and 13.6kHz are of the order of ±3km at 300–400km from a transmitter. For night conditions, errors that are multiples of a lane width (15km for 10.2kHz and 11km for 13.6kHz) will be experienced.

DOI:10.1049/piee.1970.0010

出版商:IEE    

年代:1970

数据来源: IET