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Unformatted text preview: 6.003: Signals and Systems Lecture 24 May 6, 2010 6.003: Signals and Systems Course VI Underground Guide Please give us and future students feedback on 6.003 by participating Modulation in the Course VI Underground Guide Survey: https://sixweb.mit.edu/student/evaluate/6.003-s2010 May 6, 2010 Communications Systems Signals are not always well matched to the media through which we wish to transmit them. signal applications audio telephone, radio, phonograph, CD, cell phone, MP3 video television, cinema, HDTV, DVD internet coax, twisted pair, cable TV, DSL, optical fiber, E/M Amplitude Modulation Amplitude modulation can be used to match audio frequencies to radio frequencies. It allows parallel transmission of multiple channels. x 1 (t) x 2 (t) x 3 (t) z 1 (t) z 2 (t) z(t) y(t) z 3 (t) cos 1 t cos 2 t cos c t cos 3 t LPF Superheterodyne Receiver Edwin Howard Armstrong invented the superheterodyne receiver, which made broadcast AM practical. Edwin Howard Armstrong also invented and patented the “regenerative” (positive feedback) circuit for amplifying radio signals (while he was a junior at Columbia University). He also in- vented wide-band FM. Amplitude, Phase, and Frequency Modulation There are many ways to embed a “message” in a carrier. Here are three. Amplitude Modulation (AM): y 1 ( t ) = x ( t ) cos( ω c t ) Phase Modulation (PM): y 2 ( t ) = cos( ω c t + kx ( t )) t Frequency Modulation (FM): y 3...
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