EL 6183 Week No 3 - Polytechnic University EL 6183 EE 4163...

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Polytechnic University EL 6183 EE 4163 DSP lab Lab #3 DSP Applications Using the DSK board A) Objectives At the end of this lab, students will be using the skills learned in the first two labs to build the following systems: AM Modulator Voice Scrambler using the exclusive OR with C/C++ FSK modulator B) Lab Report For lab report #3, in addition to: 1
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the traditional well formatted cover page, the signed pages of this lab, the conclusion, students are expected to: include a screen capture of waveforms insert their C/C++ source codes, explain the choices made if any, etc. C) AM Modulator 1. Theoretical Review The block diagram of an Amplitude Modulator is given in the diagram of Fig 1. Fig 1: Block Diagram of an Amplitude Modulator The message m(t) is multiplied by the carrier signal to give the signal s(t) which is a Double Side Band Suppressed Carrier (DSB-SC) signal. 2
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) 2 sin( ) ( ) ( ft A t m t s π = If the spectrum of the message is represented as in Fig 2, that of the modulated signal s(t) is given by Fig 3. f max - f max f M(f) Fig 2: Spectrum of the message f o +f max f o -f max -f o -f max -f o +f max f o -f o f S(f) Fig 3: Spectrum of the modulated DSB-SC Signal If the message is sinusoidal with frequency f max , the spectrum of the modulated is given in Fig 4. f o +f max f o -f max -f o -f max -f o +f max f o -f o f S(f) Fig 4: Spectrum of the modulated DSB-SC Signal for a Sinusoidal Message To allow for easy and cheap demodulation, it is required to have an amplitude modulated signal with carrier. This is achieved by adding the carrier signal to s(t). 3
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) 2 sin( ) 2 sin( ) ( ) ( ft A ft A t m t y π + = ) 2 sin( )) ( 1 ( ) ( ft t m A t y + = as implemented by Fig 1. As long as the message is such that |m(t)|>0, the spectrum of y(t) is given by Fig 5.
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EL 6183 Week No 3 - Polytechnic University EL 6183 EE 4163...

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