Amplitude modulation

Complete description of Amplitude Modulation.

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 Modulation Theory The amplitude of a carrier signal is varied by the modulating signal whose frequency is lower than that of the carrier signal. Modulating Signal, V m (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

7. 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.

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

9. Mixer Circuit VCO Function Generator Fig.: Amplitude Modulation Transmitter Kit

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

11. 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 .

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

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