摘要:

The object of the present survey is to put forward for consideration the problems which will confront a television reconstruction committee and it is hoped that the presentation of these problems, with as much data as it has been possible to collect, will prove of value. Fig. 1 is a “genealogical tree” showing the layout of the subject.

DOI:10.1049/ji-3-1.1944.0034

出版商:IEE    

年代:1944

数据来源: IET

摘要:

As a preliminary to the problem of designing a simple wide-band short-wave aerial for omni-directional requirements, the paper briefly discusses the comparative merits of vertical and horizontal polarization when low suspension is involved. The stages leading to the development of a novel form of aerial based on known principles are outlined, and the antecedent and subsequent experimental tests are described. The factors limiting band-width are examined, and this in turn leads to an examination of the factors determining the form and dimensions of an aerial under working conditions. The economical grouping of the aerial is considered, and some particulars are given of a check on the arrangement finally adopted. Ideal polar diagrams are illustrated, and attention is devoted to the modifying effect of physical conditions on the vertical diagrams. The paper concludes with an analysis of the quasi omni-directional properties of the horizontal dipole. The mathematical treatment of the diagrams is given in the appendices, and, for consistency, a short appendix outlines the derivation of the formula for transfer loss.

DOI:10.1049/ji-3-1.1944.0040

出版商:IEE    

年代:1944

数据来源: IET

摘要:

The paper first describes the systems in most general use, and gives a brief definition of modulation requirements for telegraph services.The various sources of distortion are described; these are fading, noise, and interference from other stations, but chiefly phase distortion due to propagation over more than one route between transmitter and receiver. The on-and-off character of morse signalling enhances the difficulties which come from most sources of distortion.There follows a description of the general characteristics required in radio receivers designed for the purposes under discussion, including a description of two types of receiver in current use. This is followed by a consideration of special requirements of the recording units into which the receivers' work, with a description of a typical unit.In the discussion of both the receiver and the recording unit the special measures provided to offset the three types of distortion previously mentioned are discussed in some detail.At first sight it may appear extraordinary that the simple business of rectifying a signal and passing the resulting direct current through an ordinary telegraph relay can become so complex as the paper suggests. It is almost wholly owing to the combined effects of the three types of distortion discussed that many of the complexities have arisen. Experience has shown that the necessity of continuing high-speed working during abnormal conditions demands the comparatively complicated solution described.Diversity reception is discussed in some detail, with particular reference to the special problems of combining the automatic gain-control (a.g.c.) systems and the receiver outputs.Recording by undulator is chiefly considered in the paper as a whole, but the discussion on the effects of distortion, and the counter-measures taken, is even more applicable to machine-printing systems, since the latter have less margins of tolerance in operation.The paper concludes with an indication of the trend of development towards different methods of signalling, which may reduce difficulties of reception and recording in comparison with the old on-and-off methods of conveying intelligence.

DOI:10.1049/ji-3-1.1944.0041

出版商:IEE    

年代:1944

数据来源: IET

摘要:

With the growth of inter-continental service the provision of large numbers of circuits on submarine cables will probably become a major problem in post-war telephony, as radio telephony is unlikely to meet all requirements. In this paper, an account of the present position of submarine-cable telephony is given, and the problem of the increased utilization of cables is examined. Major progress now turns mainly on the development of suitable submerged repeaters, and details are given of a repeater recently laid in the Irish Sea by the British Post Office. This repeater is suitable for comparatively shallow waters only, but is believed to be the first submerged repeater to be included in a working cable system. By its introduction the traffic capacity of the cable has been increased from 24 to 48 circuits.

DOI:10.1049/ji-3-1.1944.0047

出版商:IEE    

年代:1944

数据来源: IET