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Unformatted text preview: UCLA Electrical Engineering Professor Jain EE 113D TA Delbert Huang Experiment 3 Modulation Techniques Purpose • To implement amplitude modulation and demodulation on the TMS320C542 DSKplus board. • To investigate frequency modulation on the DSKplus board. Introduction and PreLab Review In Experiment 3, you will write software code to perform AM modulation using the TMS 'C54x. Before the experimental procedure is outlined, work through the following questions to review your knowledge of AM modulation. You should include the answers in a discussion format in the text of your report for this experiment. 1. Amplitude modulation (AM, speci cally DSBSC) modi es the amplitude of a carrier (a sinusoid) according to the amplitude of the signal s(t)  a >(*)> y(t) (signal) ^ (AM output)  cos(2 pi Fc t) (Carrier) so that the output is simply y ( t ) = as ( t ) cos (2 πF c t ) (1) where F c is the carrier frequency and a determines the degree of modulation. 2. When implementing amplitude modulation with DSP in this experiment, we are limited by the sampling frequency Fs since any resultant frequencies that are above F S / 2 will be aliased back into the lower frequencies. Given that the input signal s ( t ) is bandlimited to frequency F , what is the range of carrier frequencies such that there is no aliasing after modulation? 3. Back to continuous time. Show that by modulating y ( t ) with c ( t ) = cos (2 πF c t ) again, we can recover s ( t ) ; this is demodulation. What (if any) ltering is necessary? (Hint: You will end up with three frequencies after modulating the signal twice. Find the one frequency that is the original and lter out the rest.) Do this question graphically using the relationships derived previously.Do this question graphically using the relationships derived previously....
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This note was uploaded on 10/20/2009 for the course EE 113D taught by Professor Briggs during the Spring '09 term at UCLA.
 Spring '09
 Briggs
 Frequency, Gate

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