摘要:

This paper is a sequel to an earlier one and recapitulates its main points, in particular the recovery in field strength that can occur on crossing a land/sea boundary. Further experimental evidence is reviewed which is in agreement with the theory but is not sufficiently strong to be conclusive. The optimum conditions for obtaining the recovery in practice are discussed, favouring the choice of a wavelength of about 4 m where the distances required are quite small, and of 100 m where the attenuation with distance in the diffraction region is much greater over land than over sea. Experiments on approximately these two wavelengths are then described which give the expected increases in field strength and show that the calculated curves fit the observations as closely as the experimental conditions warrant. In the light of this confirmation of the theory, some of its practical implications are reviewed, in particular with regard to the siting of transmitters near stretches of water in relation to their service areas, the possibilities of frequency-sharing under ground-wave conditions, and the ground-wave coverage of medium- to long-wave navigational aids.

DOI:10.1049/pi-3.1950.0039

出版商:IEE    

年代:1950

数据来源: IET

摘要:

The most important factor restricting the performance of slotted measuring lines at very high frequencies (v.h.f.) is likely to be the effect of mechanical irregularities on the probe pick-up, unless the line is unusually well-constructed. These irregularities set a lower limit to the standing-wave ratio which can be measured, and below this limit the standing-wave pattern is completely obscured. Impedances giving rise to standing-wave ratios above this limit can be measured, though the effect of the irregularities reduces the accuracy.If the line is not disturbed these irregularities will usually have a repeatable effect, and they can be compensated for by a simple multiplication, the multiplying factor varying with the position along the line but being constant for each position. It is shown in the present paper how these correction factors may be derived. The procedure described is somewhat lengthy, but once it has been carried out all that is involved in subsequent impedance measurements is a multiplication of each of the voltage readings by a tabulated factor.

DOI:10.1049/pi-3.1950.0042

出版商:IEE    

年代:1950

数据来源: IET

摘要:

The paper describes the construction of electrical capacitors, shows the importance of excluding air and moisture from the dielectric and suggests how the sealing mechanisms may be assessed. Various methods of sealing are discussed, and the factors influencing the choice of dielectric to suit the electrical circuit and its ambient conditions are considered. The life required from capacitors is related to their main uses and to the geographical locations in which they may be required to operate.

DOI:10.1049/pi-3.1950.0043

出版商:IEE    

年代:1950

数据来源: IET

摘要:

Video amplifiers, for use in modern high-definition and colour television systems, must have the best transient response possible. Theoretical considerations show that the neutralizing of the phase error produced by the “top-correction” networks normally employed, can improve the rate of rise of transients by more than 40%, and at the same time reduce “overshoot” from greater than 20% to less than 9%. In a typical example, the phase error of a 16-stage amplifier can be corrected by three sections of bridged-T network, and almost the whole of the theoretically available improvements can be obtained. A method is outlined for evaluating the phase characteristic of an amplifier with an arbitrary amplitude-characteristic, and a practical example of its application is given. Photographs of square-wave transients taken from a cathode-ray tube, may be compared with the theoretical response, and the conclusion is drawn that optimum performance in multi-stage amplifiers is to be obtained by the use of “maximally-flat” circuits with phase correction.

DOI:10.1049/pi-3.1950.0045

出版商:IEE    

年代:1950

数据来源: IET

摘要:

A recent paper by J.A. Pim describes experiments in which ultra-high-frequency sparking potentials were measured between parallel electrodes, rounded to cause breakdown in the uniform field region at the centre. Some of the curves show breakdown potentials which increase as the gap-length is reduced. In this note, an attempt is made to explain why the spark does not simply transfer to a longer gap nearer to the edges of the electrodes.

DOI:10.1049/pi-3.1950.0047

出版商:IEE    

年代:1950

数据来源: IET

摘要:

For many years it has been known that, in principle, optical lenses could have been made from non-homogeneous glass. For example, if a glass sphere of unit radius were made with refractive index varying according to the relation.μ = √(2−r2)where μ = refractive index andr= radial distance from centre, it would act as a lens with the focus on the surface of the sphere.Such non-homogeneous glass cannot be produced in practice; however, a microwave analogue has been constructed using spaced conducting sheets to produce a region of refractive index varying in accordance with the above relation.This lens, being circularly symmetrical, is free from aberrations as the feed is moved around the circumference, and is therefore suitable for wide-angle scanning. It will operate only when the direction of polarization is such that the magnetic vector is normal to the conducting sheets.

DOI:10.1049/pi-3.1950.0048

出版商:IEE    

年代:1950

数据来源: IET

摘要:

A description of the frequency characteristics of waveguides with periodic structure is obtained in a general manner from a discussion of loaded transmission lines. An equivalent circuit is analysed to obtain more detailed confirmation of the frequency characteristics. These methods are applied to periodic waveguides with systematic detuning of resonators. All the general features of these types of guide are obtained by elementary reasoning, but for specific design problems a detailed treatment based on Maxwell's field equations is required. This method is used and discussed in the design of a periodic waveguide with every third resonator detuned, for which a space harmonic exists with constant phase-velocity over a wide frequency-band. Experimental methods of checking the theoretical frequency characteristics are discussed, and the results obtained for the constant-phase-velocity guide are given.

DOI:10.1049/pi-3.1950.0053

出版商:IEE    

年代:1950

数据来源: IET

摘要:

Some problems of electron gun design are briefly discussed. The gun is analysed into two separate parts, the triode generator and the final lens, which are considered separately. Preliminary experiments show that cathode tilt in the triode has negligible effect on beam centrality and symmetry. Effects of lateral displacement and tilt of the first anode for various anode/grid spacings are experimentally determined for several types of triode geometry.The effects of displacement, tilt and deformation of the final lens are investigated. Two Appendices are given, the first discussing the experimental technique and the second applying the work to a form of ion-trap electron gun which has found wide use and which has advantages over all other forms of trap.

DOI:10.1049/pi-3.1950.0054

出版商:IEE    

年代:1950

数据来源: IET