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UBC Theses and Dissertations

Demodulator compensating networks Pritchard, John Robert Gilbertson


This thesis deals with the study of some demodulator lead-lag networks. Specifically the problem has involved analysis and design, accompanied by experimental verification of a new approach to the realization of phase-lead and phase-lag networks for application in ac servomechanisms. Analysis has been made of several circuits, different in physical layout but operating on the same basic principle. By computing the parameters which describe the step response of the particular network, an equivalent transfer function is obtained. This transfer function is the describing function for the limiting case of infinite carrier-to-signal-frequency ratio. Experimental work was done with an electro-mechanical network, capable of generating low-frequency sinusoidal-modulated signals. Phase and amplitude characteristics of an ac lead network, centred at a frequency of 400 cycles per second, were obtained. Since only in the limit Wc/Ws → ∞ can the network be represented exactly by a describing function, experimental and analytic results for the network were compared to check the limiting describing function as a practical representation.

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