摘要:

The general problem of voltage regulation under load is reviewed and the principal technical and operating characteristics of existing voltage-regulators are summarized. The problem has not been found easy of solution, as the more simple devices are restricted in scope and have other technical limitations, whilst apparatus of more general application is relatively expensive and complicated.A recent developmentis described which in principle involes an isolated and short-circuited coil moving up and down the leg of a laminated iron core over fixed coils. Smooth voltage variation over any desired range is obtained without switches, contacts, flexible leads, or windings in slots. After a discussion of the new regulator, the special features and application of regulators are considered under the separate headings of voltage control (a) in transmission and distribution circuits, and (b) for industrial and laboratory purposes.

DOI:10.1049/jiee-1.1938.0112

出版商:IEE    

年代:1938

数据来源: IET

摘要:

The major factor which hampers the progress of broadcasting is the lack of a sufficient number of channels in which to contain the increasing number of transmissions. In the present state of the art few, except local, stations can be received without interference from other broadcasting stations on frequency-contiguous channels Unless the upper frequencies of modulation of the wanted station are severely attenuated and unless, therefore, reproduction is lacking in intelligibility and naturalness. This inter-station interference can be eradicated or minimized, and quality improved as regards “top” reproduction, if all or part of one sideband of the transmitted spectrum is cut away. The cutting-away operation on the side-band, however, produces harmonic distortion in the received signals. It is the object of the asymmetricsideband system of transmission to cut away part of one sideband without introducing audible harmonic distortion.The paper gives a quantitative analysis which shows how asymmetry, either of phase or of magnitude, between two sideband components, created by any given modulation component, is related to harmonic distortion; and it is shown that this distortion is proportional, over a large range of values, to depth of modulation. The nature of the sound spectrum is such that the intensities in the upper register are much less than those in the lower middle register. Since the degree of asymmetry between counterpart sideband components is a measure of the attenuation of the cut-away sideband, this attenuation can be increased as the modulation frequency is made greater. This is tantamount to saying that, as the sideband frequency becomes more and more removed from the carrier frequency, it may be more and more attenuated while the distortion can be made to remain constant and small. Thus in asymmetric technique the outer parts of one sideband may be removed without the introduction of audible distortion.Curves are derived, based upon the evaluation of expressions given in the quantitative analysis, which show the required attenuation-constant of niters which cut away part of one sideband but produce no more than a constant distortion. It is proved that phase asymmetry between counterpart sidebands may give rise to more serious distortions than are created by magnitude asymmetry acting alone, and a network is described which keeps phase asymmetry to a minimum and yet gives a close approximation to the required attenuation.Accounts are given of practical tests wherein the quality of reproduction obtainable from an asymmetric transmitter is compared with that given by orthodox modulation. While it is true that a highly trained ear may, on rare occasions, be able to detect some slight differences between the two types of reproduction, when they are directly compared, the general public would be quite incapable of so doing, even if they possessed receiving apparatus so free from distortion itself as to give them an opportunity to do so. It is pointed out that it is better to face the occasional minute deteriorations in quality given by the asymmetric system than to suffer from the continuous hissing and splitting sounds brought about by existing inter-station interference.In the latter part of the paper an analysis is given which shows that the asymmetric system has three possible applications to space broadcasting as it is practised to-day, namely (1) It could be used to allow carrier difference frequencies of the order of 11–12 kc. without introducing any sideband overlap interference. (2) It could be applied to existing conditions, where carrier difference frequencies are of the order of 9 kc, and would reduce inter-station interference to the order of one-tenth its present value. (3) If existing interferences are considered to be tolerable, then carrier difference frequencies can be reduced to 6 kc. without increasing interference above its existing values; this implies that 11/2; times the number of stations workingin Europe to-day on exclusive waves could be accommodated in the existing waveband.It is suggested, finally, that a policy could be adopted such that the introduction of the asymmetric system would encourage receiver development along lines wherein, by an augmentation of only the carrier component at the detector, all distortion due to the use of an asymmetric spectrum would be eliminated. Thus an evolution might be envisaged which led to the introduction of the ideal carrier and single-sideband type of transmission when all receivers were adapted to reduce the resulting distortion to a tolerable amount.

DOI:10.1049/jiee-1.1938.0118

出版商:IEE    

年代:1938

数据来源: IET

摘要:

This paper is concerned with the fluctuations generated in networks with non-uniform temperature distribution, Experiments are described which verify a formula relating to thermal fluctuations deduced in an earlier paper. The simplified representation adopted in that paper is fully substantiated: the fluctuations are shown to be independent of the temperature of reactive circuit elements.Coexistent thermal and thermionic fluctuations are then discussed. They are assumed to be mutually independent, and experiments are described which verify this hypothesis. A representation of thermionic fiuchiations is proposed analogous to that adopted for thermal fluctuations, and a general formula applicable to certain classes of networks containing thermionic valves is deduced.This formula is applied in a concluding section to a wideband photocell amplifier. Various practical recommendations are made which yield improved signal/noise ratios.

DOI:10.1049/jiee-1.1938.0120

出版商:IEE    

年代:1938

数据来源: IET

摘要:

The following paper describes the development of simple experimental direction-finders for wavelengths between 6 and 10 metres, and their use in an investigation of the accuracy of direction-finding on these wavelengths. It is shown that the inherent accuracy of the instruments is well within the limits of ± 2°, while their sensitivity is sufficient for observation on an experimental 50-watt transmitter at ranges up to 22 miles over flat ground. Bearings have also been taken on signals emanating from London television transmitters, blindlanding beacons, and also from commercial and amateur transmitting stations some 3,000 miles away.Detailed experiments have shown that the site on which the direction-finder is used must be clear of obstacles, particularly trees and vertical wires, for a radius of at least 50 to 100 yards; and there are indications that similar conditions are necessary for the site of the transmitter. When such conditions are satisfied, the bearings observed at distances up to 22 miles from the transmitter may be in error by as much as 8°, although in the majority of cases the error was less than 2°. Such errors tend to diminish in magnitude as the range increases, and they may or may not be affected by small changes in position of the direction-finder, by changes in frequency of the transmitter, or in the orientation of the transmitting aerial. For a given set of conditions, the changes in bearings observed from day to day do not exceed about 2° for ranges of 20 miles, although in some long-distance observations made on signals from American stations at a range of 3,000 miles the variations in bearings were much larger.A brief study has been made of the behaviour of the loop direction-finder when horizontally polarized waves are emitted at the transmitting station. It is shown that the errors experienced in this case can be almost entirely eliminated by the use of a rotating spaced vertical aerial arrangement in place of the loop. The evidence resulting from the use of this Adcock type of direction-finder indicates that the errors with the loop set are due to the reception of horizontally polarized waves.

DOI:10.1049/jiee-1.1938.0121

出版商:IEE    

年代:1938

数据来源: IET

摘要:

The paper gives an account of some systematic measurements of the lateral deviations of wireless waves received at Slough from various short-wave transmitters over a period of several months. The measurements were made by means of a spaced-aerial direction-finder of the four fixed-loop type, and the first part of the paper is devoted to a description of the apparatus, together with an account of its performance in respect of instrumental accuracy, pick-up factor, and other characteristics.The second part of the paper describes the measurements themselves, which were made photographically from a cathoderay oscillographic goniometer. Some of the observations were made on pulse transmissions from Nauen (Λ = 30 m.) and Dorchester (Λ = 37.3 m.), and the remainder on continuouswave transmissions from Zeesen (Λ = 31.4m.), Prague (Λ = 44.6 m.), and various American stations.The results obtained show that the variations in bearings which arise from instrumental causes do not exceed about 2°, and are usually of the order of 1°. The records demonstrate that lateral deviation occurs for the above cases to an extent which depends on the range and type of the reflected waves observed. Deviations of 10° to 20° were recorded from the more distant stations, while in the case of Dorchester, distant 160 kilometres, the deviations were as much as 50° on occasions. From a study of these observations it is concluded that the effective points of reflection at the ionosphere may be as much as 50–100 km out of the great-circle path.

DOI:10.1049/jiee-1.1938.0122

出版商:IEE    

年代:1938

数据来源: IET

摘要:

Polarized telegraph relays have been used since the early days of the telegraph, but information regarding the design has hitherto been limited practically to a discussion of static conditions only.The paper discusses static and dynamic conditions of polarized telegraph relays. From the point ofview of performance relays are divided in two classes, viz. those with stiff and those with springy tongues. It is shown that a satisfactory performance as regards short transit time and freedom from chatter can only be obtained with relays of the second class. The necessity for damping the motion is pointed out.In the latter part of the paper a practical design based on the theoretical part of the paper is described, and various test methods are discussed with regard to this design.

DOI:10.1049/jiee-1.1938.0124

出版商:IEE    

年代:1938

数据来源: IET