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Lab 2 Amplitude Modulation

This document provides information about a lab experiment on amplitude modulation (AM) using MATLAB. It discusses the theory behind AM, including how an AM signal is generated by varying the amplitude of a carrier signal based on an audio signal. The objectives are to generate and demodulate an AM signal using Simulink. Steps are outlined to design the Simulink model for AM modulation and demodulation based on the mathematical equations provided. Output waveforms will be captured and discussed at the modulator and demodulator stages.

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77 views4 pages

Lab 2 Amplitude Modulation

This document provides information about a lab experiment on amplitude modulation (AM) using MATLAB. It discusses the theory behind AM, including how an AM signal is generated by varying the amplitude of a carrier signal based on an audio signal. The objectives are to generate and demodulate an AM signal using Simulink. Steps are outlined to design the Simulink model for AM modulation and demodulation based on the mathematical equations provided. Output waveforms will be captured and discussed at the modulator and demodulator stages.

Uploaded by

alif fuden
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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FACULTY OF ELECTRONIC AND COMPUTER ENGINEERING

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

FAKULTI KEJURUTERAAN ELEKTRONIK DAN


BENG 3211
KEJURUTERAAN KOMPUTER

ELECTRONIC ENGINEERING LAB 3

BENG 3211

ELECTRONIC ENGINEERING LAB 3

LAB 2 : AMPLITUDE MODULATION (AM)


LAB 2: Amplitude Modulation (AM)

Department of Electronic Engineering


1.0 Objectives
Generation of modulation and demodulation of an Amplitude Modulation (AM) signal
using MATLAB.

2.0 Theory
Amplitude Modulation (AM) is a process that a high-frequency carrier signal is modulated
by a low-frequency modulating signal (usually an audio). In amplitude modulation the
carrier amplitude varies with the modulating amplitude, as shown in Figure 5.1.

Vmax

Vmin

Figure 5.1: AM signal

If the audio signal is Vm cos(2f m t ) and the carrier signal is Vc cos(2f c t ) , the amplitude-
modulated signal can be expressed by:
V AM (t )  Vc 1  ma cos(2f m t )cos(2f c t ) (5.1)

where Vm = audio amplitude Vc = carrier amplitude

f m = audio frequency f c = carrier frequency

m a= modulation index = Vm / Vc

Rewriting (5.1), we obtain


1
V AM (t )  Vc ma cos(2 ( f c  f m )t )  cos(2 ( f c  f m )t )  Vc cos(2f c t ) (5.2)
2
The first term on the right side of (5.2) represents double sideband signal and the second
term is the carrier signal. According to (5.2), we can plot the spectrum of AM modulated
signal as shown in Figure 5.2.

Figure 5.2: Spectrum of AM signal

In an AM transmission the carrier frequency and amplitude always remain constant, while
the sidebands are constantly varying in frequency and amplitude. Thus, the carrier
contains no information since it never changes. This means that the carrier power is a
pure dissipation when transmitting an AM signal. Thus, the transmitting efficiency of
amplitude modulation is lower than that of double-sideband suppressed carrier (DSB-SC)
modulation, but the amplitude demodulator circuit is simpler.

The m a in (5.1), called modulation index or depth of modulation, is an important


parameter. When m is a percentage, it is usually called percentage modulation. It is
defined as
Vm
ma   100% (5.3)
VC

It is difficult to measure the ADC in a practical circuit so that the modulation index is
generally calculated by:
Vmax  Vmin
ma   100% (5.4)
Vmax  Vmin

where Vmax  Vc  Vm and Vmin  Vc  Vm , as indicated in Figure 5.1.

As mentioned above, audio signal is contained in the sidebands so that the greater the
sideband signals the better the transmitting efficiency. From (5.2), we can also find that
the greater the modulation index, the greater the sideband signals and the better the
transmitting efficiency. In practice, the modulation index is usually less or equal to 1. If m
a> 1, it is called over modulation.

3.0 Procedure
Design the Simulink Model of AM modulation and demodulation. As it is clearly seen that
the AM model is exactly based upon the mathematical foundation provided in the
theoretical section. Based on the model, execute the output at the AM Modulator and at the
AM Demodulator as the result of this experiment.

4.0 Discussion and Conclusion


Discuss the steps taken to generate the output waveform of AM for modulation process
and demodulation process. Conclude your observation as the conclusion.

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