摘要:

Considerable progress has been made in the development of broadcast receivers over the 10-year period 1929 to 1939, the chief features of which have been the almost complete supersession of the straight r.f. receiver by the superheterodyne and the increase in the number of accessory circuits. Design has been influenced to a great extent by the fact that the sales market consisted of a large majority of purchasers of first receivers. This has rather tended to over-emphasize the accessory circuit (which can be made a good selling point) at the expense of basic design and the potential user's needs. With market saturation approaching, replacements must become a larger and larger proportion of the total sales, and this should give the designer an opportunity of producing receivers calculated to fulfil the more exacting requirements of the user.This paper is intended to assist the designer in taking stock of the present position and is divided into two main sections, dealing with past and probable future developments. Part 1, compiled from an examination of over 1 000 circuit diagrams, is a review of receiver circuits which have stood the test of production. The receiver is analysed stage by stage in the general discussion preceding the detailed examination of typical circuits, the salient features of which are listed separately. Representative examples of the most popular types of present-day receivers and a short note on performance specification complete the section.Part 2 is concerned with some fundamental problems and the lines of possible development. Selectivity, fidelity, electrical interference and automatic accessory circuits for volume, frequency, selectivity and remote control are some aspects of receiver design to which attention is devoted. After a short discussion on performance specification deficiencies, the predominating influence of transmitter characteristic on the overall selectivity of the complete transmission chain is stressed. Part 2 concludes with a suggestion for improving broadcasting conditions by group allocation of wavelengths.

DOI:10.1049/ji-3-1.1941.0009

出版商:IEE    

年代:1941

数据来源: IET

摘要:

This paper discusses some of the more important applications of the quartz crystal in the telecommunication art. In particular, the applications of both quartz oscillators and resonators by the Radio Branch of the Post Office are outlined and the performance of representative equipments incorporating crystals is described. In view of their importance, the methods which have been developed in the Department for the production of the necessary quartz oscillators and resonators are considered in some detail.The paper is divided into an Introduction and four Parts. In the Introduction, the scope of the paper, the quartz crystal and a standard nomenclature are considered. Quartz oscillators and their application to frequency control are considered in Part 1. Part 2 discusses the quartz resonator and some of its uses in frequency measurement and frequency selection. The production of quartz oscillators and resonators is briefly described in Part 3, while Part 4 is concerned with anticipated future development in both production and application.

DOI:10.1049/ji-3-1.1941.0011

出版商:IEE    

年代:1941

数据来源: IET

摘要:

This paper outlines various methods which can be used for the production of interlaced signals by apertured-disc film scanners. A novel arrangement using an intermittent-magnification optical system is described, and details are given of a complete transmitter according to this method. The continuously moving film is illuminated by a split optical system to remove picture flicker, and a device is included for the exact compensation of film shrinkage.Comprehensive details are given of the construction of highspeed discs, and of punches and dies for the production of scanning holes only 30–40 microns in diameter. It is shown that, for a given noise level at the input of the vision channel, the scanning resolution obtainable is proportional to the strength/density ratio of the disc material, and the limit is well above present television standards.Synchronizing signals are all derived from the disc, and various mechanical arrangements are shown by which multiple and sub-multiple frequency signals are available for control purposes.

DOI:10.1049/ji-3-1.1941.0014

出版商:IEE    

年代:1941

数据来源: IET