Basics of AM

1. Amplitude Modulation

2. Amplitude Modulation
• Modulating signal- Audio signal
• Carrier signal –Radio frequency
signal
• Electronic device used for
modulation- Modulator
• Frequency and phase of the
carrier is not changed.

3. Amplitude Modulation

4. Mathematical representation of Amplitude Modulation
 AM is defined as system of modulation in which the
instantaneous value of the carrier changes in
accordance with amplitude of the modulating
signal.
 instantaneous value of the modulating signal
em =Em sinωmt
 em – instantaneous amplitude of the modulating signal
 Em – maximum amplitude of the modulating signal
 ωm = 2πfm – angular frequency of the modulating signal

5. Contd.
 instantaneous value of the carrier signal
ec =Ec sinωct
 ec – instantaneous amplitude of the carrier signal
 Ec– maximum amplitude of the carrier signal
 ωc = 2πfc – angular frequency of the carrier signal

6. Contd.
 instantaneous value of the amplitude modulated signal
eAM =EAM sinωct
 eAM – instantaneous amplitude of the modulated signal
 EAM– maximum amplitude of the modulated signal
 ωc = 2πfc – angular frequency of the carrier signal
EAM

7. Contd.

8. Contd.

9. Example
 A carrier wave of frequency 10MHz and peak value 10Volts is amplitude
modulated by a 5KHz sine wave of amplitude 6Volts. What is the modulation
index?

10. Frequency Spectrum of AM Wave

11. Total Power of amplitude modulated wave