AM Generation using SimulinkManoj Shenoy
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 (Sc) = Acsin(2πfct)
- Message signal (Sm) = Amsin(2πfmt) # fm must be smaller than fc
When carrier amplitude is altered with respect to message signal,
- Modulated Signal = (Ac+ Amsin(2 πfmt))*sin(2 πfct)
In terms of modulation index (m=Am/Ac) the equation becomes
- Modulated signal= (1+ msin(2 πfmt))*Acsin(2 πfct)
- Ac = Carrier signal amplitude
- Am = Message signal amplitude
- fc= Carrier frequency
- fm =Message frequency
For generating AM we just have to implement the equation of AM in block level.
Analyzing the equation we need,
- Carrier Signal Source
- Message Signal Source
- Blocks for viewing the signals – Scope
- Product Block
- Summer Block
- 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
- Simulink –> Sink –> Scope
Product and Summer Block
- Simulink –> Math Operations–> Product
- Simulink –> Math Operations–> Summer
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