Amplitude modulation (AM) is a one of the conventional technique used to transmit message signals using a carrier wave. The amplitude or strength of the high frequency carrier wave is modified in accordance with amplitude of the message signal. If you are a newbie to Simulink, please read our article Introduction to Simulink.

First of all lets get into the basics..

• Carrier signal (S_c) = A_csin(2πf_ct)
• Message signal (S_m) = A_msin(2πf_mt)   # fm must be smaller than fc

When carrier amplitude is altered with respect to message signal,

• Modulated Signal = (A_c+ A_msin(2 πf_mt))*sin(2 πf_ct)

In terms of modulation index (m=Am/Ac) the equation becomes

• Modulated signal= (1+ msin(2 πf_mt))*A_csin(2 πfct) 

Where,

• A_c = Carrier signal amplitude
• A_m = Message signal amplitude
• f_c= Carrier frequency
• fm =Message frequency

Generating AM in Simulink

For generating AM we just have to implement the equation of AM in block level.

Blocks Required

Analyzing the equation we need,

1. Carrier Signal Source
2. Message Signal Source
3. Blocks for viewing the signals – Scope
4. Product Block
5. Summer Block
6. Constant Block

We can find these blocks in the following locations of Simulink Library…

Carrier, Message, Constant blocks

• Simulink –> Sources –> Sine wave
• Simulink –> Sources –> Constant

View Block

• Simulink –> Sink –> Scope

Product and Summer Block

• Simulink –> Math Operations–> Product
• Simulink –> Math Operations–> Summer

Block Diagram

Block parameters can be changed by selecting the block and parameter that I used are given below..

• Carrier Signal frequency = 2*pi*25 and sampling time=1/5000
• Message Signal frequency = 2*pi and sampling time=1/5000
• Amplitudes of both signals are 1

Output Waveforms