This document discusses amplitude modulation (AM). It defines AM as a modulation technique where the amplitude of a carrier signal is varied in accordance with a message signal. It describes the theory behind AM mathematically and discusses generating AM signals in a lab using a function generator, voltage controlled oscillator, and mixer circuit. It also lists the components used, shows waveshapes of AM, and discusses advantages/disadvantages and applications of AM including broadcasting, mobile communications, and aircraft communications.

1. AMPLITUDE MODULATION
COURSE NO.: EEE 3218
COURSE TITLE: COMMUNICATION ENGINEERING II
SESSIONAL

2. Content
 What is Modulation?
 Why is Modulation needed?
 Classification of Modulation
 What is Amplitude Modulation?
 Amplitude Modulation Theory
 Waveshapes of AM
 Generation of AM in Laboratory
 List of Components
 Amplitude Demodulation Kits & Outputs
 Advantages & Disadvantages
 Applications

3. What is Modulation?
Modulation is the process by which the characteristics of a
carrier signal is varied according to the message signal.
Why is Modulation Needed?
 Message signal is incompatible for direct transmission. So its
strength has to be increased by modulation with a high frequency
carrier signal which doesn’t affect the parameters of message
signal.

4. Classification of Modulation
Amplitude Modulation
Frequency Modulation
Phase Modulation
What is Amplitude Modulation?
Amplitude Modulation is a modulation technique where the amplitude
of a carrier signal is varied in accordance with the message signal
to obtain a modulated signal.
Angular Modulation

5. Amplitude ModulationTheory
The amplitude of a carrier signal is varied by the modulating signal
whose frequency is lower than that of the carrier signal.
Modulating Signal, Vm (t)=VmSin(2*pi*fm)t
Carrier Signal, Vc(t)=VcSin(2*pi*fc)t
Modulated Signal, V(t)=(Vc+ VmSin(2*pi*fm)t)*Sin(2*pi*fc)t
=VcSin(2*pi*fc)t+((m*Vc)/2)*Cos(2*pi*fc-2*pi*
fm)t – ((m*Vc)/2) )*Cos(2*pi*fc+2*pi*fm)t
Here, m(modulation index)=Vm/Vc
For perfect modulation, m=1
For Under Modulation, m < 1
For Over Modulation, m > 1

6. Waveshapes of AM

8. Generation of AM in Laboratory
A function generator was used to generate a modulating signal and a voltage
controlled oscillator (VCO) was used to generate a carrier signal. Then, using
a mixer circuit, a modulated signal was generated.
Varying the amplitude of modulating signal, there were three types of modulation.
They were:
 Perfect Modulation
 Under Modulation
 Over Modulation
In overmodulation, one kind of distortion was occurred.

9. List of Components
Function Generator
Voltage Controlled Oscillator(VCO)
Mixer Circuit
Wires
Oscilloscope

10. Mixer CircuitVCO
Function Generator
Fig.: Amplitude Modulation Transmitter Kit

11. Fig. Perfect Modulation(m=1) Fig. Over Modulation(m=2)
Fig. Under Modulation(m=0.6)

12. Advantages
AM transmitters are less complex.
AM receivers are cost-effective.
Disadvantages
Not efficient in terms of power usage.
Not efficient in terms of bandwidth.

13. Application of AM
Broadcasting of both audio and
video signals.
Mobile, radio communications.
Aircraft communications.

14. Thank You