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6.02 Spring 2008
1 of 29
Lab #2
Massachusetts Institute of Technology
Dept. of Electrical Engineering and Computer Science
Spring Semester, 2008
6.02 Introduction to EECS 2
Lab #2: Modulation and Filtering
Goal:.
...................................................................................................................................
2
Instructions:.
........................................................................................................................
2
Prelab: .
................................................................................................................................
3
A. Understanding Modulation .
.......................................................................................
3
B. Understanding Demodulation .
...................................................................................
7
C. Low Pass and Band Pass Filter Design.
.....................................................................
9
D: Exercises:
Filtering and Modulating Signals With Nonzero Bandwidth.
...............
17
Lab Exercises (9am  noon and 2pm – 5pm, Wed., February 20, 2008):.
........................
18
A. Objectives.
................................................................................................................
18
B. Introduction.
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18
C. Building a FDM Receiver .
.......................................................................................
20
D. Exercises .
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21
Example Interview Questions.
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27
Checkoff for Lab 2 .
.........................................................................................................
29
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Lab #2
Goal:
Learn principles of modulation and filtering through hands on interaction with Matlab
and the USRP board. In particular, you will become familiar with a wireless
communication scheme known as frequency division multiplexing, and will write Matlab
code to receive voice signals that have been modulated to different frequency bands.
You will also examine the issue of frequency offset in demodulation.
Instructions:
1.
Complete the Prelab exercises
BEFORE
Wednesday’s lab (February 20, 2008).
Complete Tasks 16, and for each task save the plots that you produce and hand
in the plots at the beginning of the lab.
2.
Complete the activities for Wednesday’s lab (see below) and get checked off by
one of the TAs.
Be sure to work in pairs.
3.
Look over the example interview questions, and be prepared to answer questions
similar to them after you finish the lab on Wednesday.
6.02 Spring 2008
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Lab #2
Prelab:
Modulation
,
demodulation
, and
filtering
are integral to the frequency division
multiplexing (FDM) communication system you will be building in Lab 2.
The purpose
of these prelab exercises is to familiarize you with the implementation of these signal
processing operations using simple sinusoidal signals.
A. Understanding Modulation
The purpose of this exercise is to understand the mechanics of modulation and
demodulation as well as to study the effects of these operations on signals in the time and
frequency domains.
We will study the modulation and demodulation of a 1 Hz sinusoid
by 10 Hz.
Consider the signal
)
*
2
cos(
)
(
t
t
x
π
=
.
This is a sinusoid with amplitude of 1 and
frequency of 1 Hz.
Create a Matlab file called “modulation.m” and enter the following
commands to create and visualize x(
t
) in the time domain.
Your code should generate
Figure 1.
Fs = 1000;
% Sample Frequency in Hz
t = 0:1/Fs:5;
% Time vector from 05 seconds in increments of
% 0.001 seconds (eg. 0 0.001, 0.002, 0.003 .
..)
x = cos(2*pi*1*t);
% Cosine with amplitude 1 and frequency 1 Hz
figure(1)
% Create Figure 1
plot(t,x)
% Plot Signal
x(t)
in Figure 1
title(
'TimeDomain'
);
% Add Title
TimeDomain
to Figure 1
xlabel(
'Time (sec)'
);
% Add
Time (sec)
as xaxis label of
Figure 1
ylabel(
'Amplitude'
);
% Add
Amplitude
as yaxis label of Fig. 1
axis([0 1 2 2])
% Set xaxis range [01] sec and
%
yaxis range [2 2]
Figure 1
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Lab #2
Now lets visualize the magnitude of the spectrum of x(
t
).
Since x(
t
) is a real signal, the
magnitude of its spectrum is an even function (symmetric about 0 Hz).
We expect to see
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This note was uploaded on 08/23/2009 for the course EECS 6.02 taught by Professor Terman during the Spring '08 term at MIT.
 Spring '08
 Terman
 Computer Science, Electrical Engineering

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