DOI:10.1049/ree.1982.0022

出版商:IERE    

年代:1982

数据来源: IET

摘要:

The paper describes the initial stages of the development of microprocessor-based equipment to convert pages of teletext and viewdata information into forms suitable for blind users. The paper concentrates on the development of hardware and software to convert the information into Grade I Braille, which is then displayed on a refreshable row of electrically activated pins, arranged in standard Braille configuration. Initial reactions to the device have been encouraging, and the paper concludes with a discussion of development work now in progress.

DOI:10.1049/ree.1982.0024

出版商:IERE    

年代:1982

数据来源: IET

摘要:

The work reported here is concerned with measuring and trying to predict coupling between coaxial cables. The surface transfer impedance per unit length, ZT, is the parameter that determines how the signal gets into and out of the coaxial cables: this is measured in the frequency range from 100 kHz to several GHz in some cases. The third circuit, outside the coaxial cables, consists of the outers of the sending and victim cables and any other conducting and dielectric material in the vicinity. A lumped representation of the tertiary serves well at frequencies for which the length is less than a tenth of a wavelength; distributed circuit models are useful at all frequencies.

DOI:10.1049/ree.1982.0026

出版商:IERE    

年代:1982

数据来源: IET

摘要:

Ruze and Rotman lenses are types of parallel-plate lens which can be used to form multiple beams for antenna arrays. An algebraic analysis is used to relate the different orders of phase aberration to the lens contours, and shows that lenses with zero second- and third-order aberrations can be designed. For a given array length and beam scan angle requirement, the analysis determines the minimum lens size and simplest design which can be used.

DOI:10.1049/ree.1982.0027

出版商:IERE    

年代:1982

数据来源: IET

摘要:

Classes of array codes for correcting bursts of errors, bursts of erasures, and mixed error-and-erasure bursts, are described. A specific example of a burst-error-correcting array code, and its decoder, is given. These codes have relatively high rates, small decoding delay, simple encoding and decoding algorithms, and are capable of high-speed operation. Array codes have a wide range of application in digital communications.

DOI:10.1049/ree.1982.0028

出版商:IERE    

年代:1982

数据来源: IET

摘要:

Channel assignment procedures for mobile radio systems are usually based on the assumption of equal spacing in frequency between all available channels, and it is customary to argue that the growing demands for greater numbers of channels in the limited spectrum available must be met by dividing the present separation interval of 12.5 kHz by two.Such a measure would however demand major changes in the specification and design of equipment and the purpose of the present paper is to consider alternative strategies for channel frequency assignment which might increase the available number of channels while making less stringent demands on improvements in equipment performance. A typical computed result shows that, by reducing channel bandwidth by 20% and utilizing an assignment strategy based on multiples of a 2.5 kHz increment, the bandwidth needed to accommodate eight channels with freedom from third-order intermodulation interference is reduced from 437.5 kHz to 200 kHz.

DOI:10.1049/ree.1982.0029

出版商:IERE    

年代:1982

数据来源: IET