ELECTRICAL ENGINEERING STUDIES

COLLEGE OF ENGINEERING
UNIVERSITI TEKNOLOGI MARA

BASIC COMMUNICATION ENGINEERING

(ECM241)

MODULE 1
AMPLITUDE MODULATION (AM)

COURSE OUTCOME (CO) - PROGRAMME OUTCOME (PO)

CO3 Develop the proper waveform and spectrum of analog and digital transmission techniques
based on the applied modulation or multiplexing.(P3)
PO5 Apply appropriate techniques, resources, and modern engineering and IT tools to well-
defined engineering problems, with an awareness of the limitations.

OUTCOMES
1. To display the modulated and demodulated signal of AM.
2. To measure the spectrum of AM in frequency range.

EQUIPMENT
1. MATLAB software
2. PC or laptop

THEORY
Amplitude Modulation (AM) is the process of varying the amplitude of the Radio Frequency
carrier wave by the amplitude variations of a modulating signal or the information signal. The
instantaneous value of the carrier amplitude changes in accordance with the amplitude
variations of the modulating signal. Figure 1.1 shows how an AM signal is generated when a
carrier signal is modulated by a modulating signal.

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 Figure 1.1: (a) Modulating signal (b) Carrier signal (c) Modulated signal

AM Modulator and Demodulator

An example of AM Modulator is diode modulator as shown in Figure 1.2, which consists of a
resistive mixing network, a diode rectifier, and an LC tuned circuit. A demodulator or a detector
is a circuit that accepts a modulated signal and recovers or detect the original modulating
information. The simplest AM demodulator is a diode detector as shown in Figure 1.3.

Figure 1.2: Diode Modulator

D1
Demodulated
AM signal
signal R1 C1

Figure 1.3: Diode

DetectorAM Signal Characteristics and Parameters

In AM signal, the amplitude of the carrier wave varies sinusoidally between the values of ( Vc
+ Vm ) and ( Vc - Vm ) as shown in Figure 1.4, where Vc is the peak value of the carrier signal,
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 while Vm is the peak value of the modulating signal. The ratio of the modulating signal voltage
to the carrier voltage is called modulation index, ma. The value of modulation index also can
be obtained from the maximum and minimum value of modulated signal and can be expressed
as percentage as follows:

V V V
m %m 100%
V V V

In practice, it is desirable to operate with as closed as to 100 percent modulation so that the
maximum information signal can be transmitted.

Figure 1.4: AM Modulated Signal

AM frequency spectrum which is a plot of amplitude versus frequency can be obtained from
equation (1.1). It can be seen that an AM wave contains the carrier and the two sidebands
namely lower side band (LSB) and upper side band (USB) as illustrated in Figure 8.5. The
difference between USB and LSB will determine the bandwidth of the AM signal.

maVc maVc
AM (t) V sin 2 f t cos 2 ( f c f m )t cos 2 ( f c f m )t (1.1)

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Figure 1.5: AM Frequency Spectrum

4
PROCEDURES

SIMULINK BLOCK DIAGRAM SETUP

a) First, open MATLAB, the desktop will appear in its default layout (Figure 1.6 (a)). Then, click
Simulink icon to open the blank window of the Simulink. After that, save the blank window with
any suitable name i.e DSB_AM.
b) To choose the block, open Simulink Library Browser as shown in Figure 1.6 (b).

(a) (b)
Figure 1.6: (a) MATLAB desktop layout (b) Simulink Library Browser

c) Next, in the Simulink Library open Communications System Toolbox > Modulation >
Analog Passband Modulation (Figure 1.7 (a)). Then, click and drag "DSB AM Modulator
Passband" block into DSB_AM window that has been created earlier. Repeat the same step for
"DSB AM Demodulator Passband" block. The DSB_AM window can be seen in (Figure 1.7 (b)).

(a) (b)
Figure 1.7: (a) Communication System Toolbox (b) DSB AM Modulator and
Demodulator

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d) Next, in the Simulink Library select Simulink > Sources > Signal Generator and drag
the "Signal Generator" block in the DSB_AM window (Figure 1.8 (a) and (b))

(a) (b)
Figure 1.8: (a) Signal Generator block from Sources (b) Signal Generator in DSB_AM
window

e) Then, in the search menu, type "Zero-Order Hold" (Figure 1.9 (a)) and then press Enter.
Drag the "Zero-Order-Hold" block into DSB_AM window as shown in Figure 1.9 (b).

(a) (b)
Figure 1.9: (a) Searching of Zero-Order-Hold block (b) Zero-Order-Hold in DSB_AM
window

f) To measure the signals in the time range, a measuring instrument is required. Select
Simulink > Sinks > Scope and drag the "Scope" block in the DSB_AM Window (Figure
1.10).

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 Figure 1.10: Scope block added in DSB_AM window

g) To display the result in frequency range, a spectrum analyzer is required. In the search
menu, type "spectrum" (Figure 1.11 (a)) and then press Enter. Drag the "Spectrum Analyzer"
block into DSB_AM window as shown in Figure 1.11 (b).

(a) (b)
Figure 1.11: (a) Searching of Spectrum Analyzer (b) Spectrum Analyzer block in
DSB_AM window

h) The scope should be connected to DSB AM Modulator Passband, DSB AM Demodulator

Passband and Spectrum Analyzer. To create three input ports at the scope, double click the
scope,then a scope window as shown in Figure 1.12 (a) will be opened. Go to configuration
properties, insert number 3 into the number of input ports. Click layout, select three blocks
either in vertical or horizontal direction.

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 (a) (b)
Figure 1.12: (a) Scope window (b) Configuration Properties of the Scope

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i) Next, connect all blocks as shown in Figure 1.13.

Figure 1.13: Final Circuit of Amplitude Modulation

SIMULATION PARAMETER
By double clicking the function block, the dialog box will appear. Insert the parameters
of each function block as follows:

a) "Signal Generator" block:

Figure 1.14: Signal Generator Parameter

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b) "Zero-Order Hold" block:

Figure 1.15: Zero-Order-Hold Parameter

c) "DSB AM Modulator Passband" :

Figure 1.16: DSB AM Modulator Passband Parameter

d) "DSB AM Demodulator Passband":

Figure 1.17: DSB AM Demodulator Passband

Parameter

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e) For "Scope" block in Figure 1.18, the appropriate name of the signal should be given i.e.
Modulationsignal for the first scope display. Then, insert the minimum and maximum value for
Y-limits. Then, click apply. Repeat the same steps for second and third display (Modulated
signal and Demodulated signal).

Figure 1.18: Signal Labelling

f) "Spectrum Analyzer" block:

Figure 1.19: Spectrum Analyzer Parameter

g) Repeat step (a) “Signal Generator” block – set amplitude to 0.5 Volt and the rest of the setting
remains unchanged. Then draw the displayed output in Result Sheet.

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 UiTMCPP/PKE/ECM241/Laboratory Rubric/Oct2023/Ver1

LABORATORY WORK
ELECTRICAL ENGINEERING STUDIES
COLLEGE OF ENGINEERING
UNIVERSITI TEKNOLOGI MARA
CAWANGAN PULAU PINANG
COURSE NAME: BASIC COMMUNICATION ENGINEERING COURSE CODE: ECM241
EXPERIMENT
EXPERIMENT TITLE:
DATE:
PROGRAMME
STUDENT’S NAME:
CODE:
STUDENT’S ID: GROUP:

LECTURER’S NAME:

Develop the proper waveform and spectrum of analog and digital transmission
COURSE OUTCOME (CO): CO3
techniques based on the applied modulation or multiplexing.(P3)
PROGRAMME OUTCOME Apply appropriate techniques, resources, and modern engineering and IT tools to well-
PO5
(PO): defined engineering problems, with an awareness of the limitations.
- -
KNOWLEDGE PROFILE (DK):
- -
- -
PROBLEM SOLVING (DP): - -
- -
ENGINEERING ACTIVITIES
- -
(NA):
POOR FAIR GOOD EXCELLENT
CRITERIA SUB-ATTRIBUTE SCORE WEIGHT MARKS
1 2 3 4
Handling
Unable to
Software/Equipment Handle the Handle the Handle the
handle the
Ability to demonstrate software/ software/ software/
software/
a proper use of equipment with equipment with equipment x 0.75
Demonstration setup

equipment
software/equipment moderate minimal without
even with
Experimental/

assistance assistance assistance

assistance
-
Complete
Unable to Complete Complete
constructing
Constructing Circuit construct constructing constructing
model/circuit/
Ability to construct model/circuit/ model/circuit/ model/circuit/
system coding x1
model/circuit/system system coding system coding system coding
with minimal
coding even with with moderate without
assistance
assistance assistance assistance

Complete Complete
Output Response Complete
Incomplete output output
Ability to obtain output output
output response but response but x 0.5
response using response
response with major with minor
modern tools without error
error error
Output

Complete Complete
Output Validation Complete
Incomplete output output
Ability to perform data output
output validation but validation but x 0.25
validation based on validation
validation with major with minor
the measured result without error
error error

TOTAL (MARKS) /10

RESULT SHEET :
Table 1a
Output Wave
Draw input :

Information signal

Draw display output:

AM (amplitude modulated
signal) 1st setting

Draw display output:

Spectrum Analyzer (AM

Frequency spectrum)

Table 1b
Draw display output:

AM wave (amplitude
modulated signal) 2nd
setting

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OUTPUT VALIDATION

1. Based on the AM modulated waves obtained in Table 1a and Table 1b, discuss the changes
observed in modulation index when amplitude is varied.

………………………………………………………………………………………………………….

………………………………………………………………………………………………………….

2. Measured the following items from output observed from Table 1a.

a) Vmax = ……………………………………

b) Vmin = ……………………………………..

c) Frequency for upper sideband = …………………………...

d) Frequency for lower sideband = ……………………………