Linearity of some modulation circuits.

Hately, Maurice Clifford

Abstract

The work consists of a detailed study of the methods of analogue modulation and demodulation of electrical carrier waves by amplitude and frequency, with the object of presenting improved techniques where necessary. The thesis is divided into five parts, of which the last is devoted to the conclusions. The first and second parts deal with amplitude modulation and demodulation. A novel form of mismatched diode modulator circuit is proposed to improve the linearity of such processes. Developed forms are tested with sinusoidal carrier drive. It is shown that the mismatched demodulator will eliminate distortion due to diagonal clipping. By Fourier analysis it is shown that chopped sine wave modulators, of which there are many types presently used, cannot be deeply modulated and remain linear. The mismatched modulators are re-tested with square wave drive and improved performance is obtained. The third and fourth parts are given to an examination of frequency modulation and demodulation. For applications of low cost, two simple linear frequency modulators are recommended. For receivers, a new theoretical approach to the spectrum of a frequency modulated wave is presented, in which the Bessel series are derived using a straightforward expansion technique. The sensitivity and linearity of the Foster-Seeley type discriminators are investigated in detail.

Citation

HATELY, M.C. 1975. Linearity of some modulation circuits. University of Aberdeen; Robert Gordon's Institute of Technology, MSc dissertation. Hosted on OpenAIR [online]. Available from: https://doi.org/10.48526/rgu-wt-1993292

• Thesis Type: Dissertation
• Deposit Date: Jun 27, 2023
• Publicly Available Date: Jun 27, 2023
• DOI: https://doi.org/10.48526/rgu-wt-1993292
• Keywords: Amplitude modulation; Modulators (Electronics); Modulation (Electronics)
• Public URL: https://rgu-repository.worktribe.com/output/1993292
• Award Date: Apr 30, 1975