摘要:

High-definition television was described in 1935 by the Selsdon Committee as having not less than 240 lines per picture. Public transmission of an interlaced 405-line service commenced in 1936 and lasted until 1985, having been gradually displaced by 625-line colour. Today, high definition means more than 1000 lines, and is unlikely to be broadcast from conventional terrestrial transmitters.This Address reviews the development of terrestrial television transmission technology from the, pre-war Baird/Marconi-EMI trials, through the period of post-war Band I and III expansion to the introduction of u.h.f. and the ultimate realization in the United Kingdom of one of the most highly developed and effective colour transmission networks anywhere in the world.

DOI:10.1049/jiere.1986.0001

出版商:IERE    

年代:1986

数据来源: IET

DOI:10.1049/jiere.1986.0005

出版商:IERE    

年代:1986

数据来源: IET

摘要:

Approaches to the determination of the worst-case available output power or induced voltage in a structure acting as an unintended receiving antenna are presented. Such structures fall into two categories: ‘electrically-small’ and ‘electricallylarge’, dependent on the size of the structure relative to the wavelength of the incident radiation. Electrically-small structures have simple radiation patterns; their efficiency is very low and is dominated by the ohmic loss resistance. The most realistic canonical model for this case is the loop antenna: an analysis of the relevant characteristics of this is presented, together with experimental corroboration.The results have implications for prediction of the following hazards: ignition of flammable gas mixtures; shock/burn hazards to personnel; initiation of electric detonators.

DOI:10.1049/jiere.1986.0006

出版商:IERE    

年代:1986

数据来源: IET

摘要:

Approaches to the determination of the worst-case available output power or induced voltage in a structure acting as an unintended receiving antenna are presented. Electrically-large structures have complex radiation patterns and a relatively high efficiency. The most realistic canonical model for unintended receiving antennas is the loop antenna, but when this becomes electrically-large its radiation pattern becomes difficult to predict. However, it is known that the pattern will be similar to that of the long dipole antenna and, since inefficiency effects are not significant in this case, it is acceptable to use the long dipole as the canonical model for the electrically-large case. An algorithm for computation of long dipole characteristics was developed: computed worstcase results are presented.The results have implications for prediction of the following hazards: ignition of flammable gas mixtures; shock/burn hazards to personnel; initiation of electric detonators.

DOI:10.1049/jiere.1986.0008

出版商:IERE    

年代:1986

数据来源: IET

摘要:

This paper provides an evaluation of the performance of a framed slotted ring network supporting both voice and data. An investigation based on simulation models shows the delay-throughput characteristic of pure data at various levels of voice traffic. Provided that the total number of voice slots per frame does not exceed the frame capacity, periodic entry is guaranteed to each off-hook subscriber while talking, with almost zero access delay.

DOI:10.1049/jiere.1986.0009

出版商:IERE    

年代:1986

数据来源: IET