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  • (1967) Boadle, Ronald Dean
    A television system is concerned with the faithful transmission of transient signals in a restricted bandwidth. The sine-squared pulse has proved to be a suitable test signal for such systems. The C.C.I.R.-approved method of generating such pulses uses a 7th order network, devised by W. E. Thomson, of the British Post Office. The work described herein was aimed at the development of networks with a lower distortion than the 7th order Thomson network, so that the pulse generator could be used for testing very low distortion systems and units. Ninth and eleventh order transfer functions, calculated by the Thomson method, gave impulse responses of superior shape, but the improvement in overshoot was moderate. Alternative methods, giving transfer functions with higher order numerators, were studied - in these, the pulse shapes were not quite so perfect, but the overshoots were smaller than those produced by Thomson functions of the same order. Four transfer functions were selected, and networks were synthesised from these. The filters were built up, and tested for insertion loss and impulse response. In the course of the work, a number of computer programs were written for various phases of the project. Descriptions of these are given, illustrated by flow charts, and sample calculations.

  • (1967) Hollo, Paul

  • (1968) Ruddick, Rodney Clive
    It is demonstrated that a re-timing device for binary signals can be realised using digital circuit techniques. The mechanism of regeneration through storage of input information is outlined, and the operating principles of practical systems performing this function are discussed. The input signal requirements are defined to allow design of a, practical regenerating system. Control system theory is then used to select a desired system response function whose steady state and transient performance are analysed. Tests made on the laboratory prototype system show good agreement with the mathematical analysis. Further study of the system is suggested with regard to the use of non-linear response functions in the feedback network, thereby providing an improvement of the regeneration characteristic. It is felt that an important side result arising from the work lies in the development of a digital phase difference comparator. Such a device can conveniently be constructed using integrated circuit techniques - a point of considerable interest to designers of telemetry equipment. Construction of the prototype regenerator constituted a major part of the project work as may be realised from the circuit diagrams involved. For this reason discussion of the principles of circuit operation is fairly comprehensive.