What is the bandwidth of the modulated signal

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Reference no: EM132676547

ECE 44000 Transmission of Information - Purdue University

Lab - Amplitude Modulation

Section 1: DSB-SC Simulink

This lab is a follow up from previous lab. You need to demonstrate similar modulation scheme using Simulink.
Use the same parameters from lab 4.
Use 100 kHz for the sampling frequency as you had in Lab 4.
In Simulink, obtain the spectrum analyzer plots of DTMF signal
Using DSBSC AM Modulator block, obtain the scope of DTMF signal and modulated DTMF signal. Also obtain the spectrum analyzer plot of modulated DTMF signal. (8 points).
Demodulate the signal using DSBSC AM Demodulator block with low pass filter cut off frequency of 20kHz. Obtain the spectrum analyzer plot of demodulated DTMF signal. Also obtain the time scope signal of original signal and demodulated signal .
Repeat the demodulation scheme above but change the low pass filter cut off frequency to 5kHz. Obtain the spectrum analyzer plot of demodulated DTMF signal. Also obtain the time scope signal of original signal and demodulated signal .

ADDITIONAL INSTRUCTIONS:
Make sure scope plots are zoomed in and show no more than 5ms of data
Use peak finder to identify all the frequency peaks.
Assume 50 Ohms Spectrum analyzer load.
Make sure to have your spectrum analyzer settings configured to show only one sided spectrum (positive frequency only).

Answer the following questions:
Based on what was taught in lecture session, how many peaks of demodulated signal do you expect to see? Do you see the same number of peaks in your result? If there are more peaks than expected, indicate which are going to give significant contributions.
Is the demodulated signal in phase with the original message? Why is there phase change?
Which low pass filter cut off should you use? 5kHz or 20kHz? Explain why?
What is the bandwidth of the message?
What is the bandwidth of the modulated signal?

Section 2: SSB Simulink

For either upper sideband modulation or lower sideband modulation, answer the following questions:
Does the spectrum looks like single side band or double side band modulation? Explain why! Identify which of the peak(s) have significant contribution? (You need to convert dBm into Watts and show why you choose the peaks). Is this expected? Explain
What is the bandwidth of the message?
What is the bandwidth of the modulated signal?
What are the main advantage of SSB over DSB modulation?

Random Variables - Amplitude Modulation

1. Based on what was taught in lecture session, how many peaks of demodulated signal do you expect to see? Do you see the same number of peaks in your result? If there are more peaks than expected, indicate which are going to give significant contributions.
2. Is the demodulated signal in phase with the original message? Why is there phase change?
3. Which low pass filter cut off should you use? 5kHz or 20kHz? Explain why?
4. What is the bandwidth of the message?
5. What is the bandwidth of the modulated signal?

Does the spectrum looks like single side band or double side band modulation? Explain why! Identify which of the peak(s) have significant contribution? (You need to convert dBm into Watts and show why you choose the peaks). Is this expected? Explain
What is the bandwidth of the message?
What is the bandwidth of the modulated signal?
What are the main advantage of SSB over DSB modulation?

Reference no: EM132676547

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