Amplitude Modulation and Demodulation
AMPLITUDE MODULATION AND DEMODULATION :
OBJECTIVE :
Study how to perform the amplitude modulation and demodulation and to calculate the modulation index for various modulating voltages.
Theory :
AMPLITUDE MODULATION :
Modulation is defined as the process by which some characteristics of a carrier signal is varied in accordance with a modulating signal. The base band signal is referred to as the modulating signal and the output of the modulation process is called as the modulation signal.
Amplitude modulation is defined as the process in which is the amplitude of the carrier wave is varied about a means values linearly with the base band signal. The envelope of the modulating wave has the same shape as the base band signal provided the following two requirements are satisfied.
1. The carrier frequency fc must be much greater then the highest frequency components fm of the message signal m (t) i.e. fc >> fm
2. The modulation index must be less than unity. if the modulation index is greater than unity, the carrier wave becomes over modulated.
3. Modulation index = (A-B)/(A+B). where A and B as shown in the figure below.
Figure 1: Designing modulation index Fig2: Amplitude modulation model graph
Design Procedure :
Modulated Signal (Under Modulation) :
Given VC = 300mV, fc = 500 KHz, fm = 1KHz.
Set modulating voltage Vm = 200mV.
Emax = 220 V, Emin = 60 V Modulation index (m) = E max - E min/ E max + Emin X 100 = 0.57%
Modulated Signal (Over Modulation) :
Given VC = 300mV, fc = 500 KHz, fm = 1KHz.
Set modulating voltage Vm = 200mV.
Emax = 320 V, Emin = 70 V Modulation index (m) = E max - E min/ E max + Emin X 100 = 1.56%
Test Procedure :
1. The power supply is connected to the collector of the Transistor.
2. Modulated Output is taken from the collector of the Transistor.
3. Calculate Emax and Emin from the output waveform.
AMPLITUDE DEMODULATION :
The
OBJECTIVE :
Study how to perform the amplitude modulation and demodulation and to calculate the modulation index for various modulating voltages.
Theory :
AMPLITUDE MODULATION :
Modulation is defined as the process by which some characteristics of a carrier signal is varied in accordance with a modulating signal. The base band signal is referred to as the modulating signal and the output of the modulation process is called as the modulation signal.
Amplitude modulation is defined as the process in which is the amplitude of the carrier wave is varied about a means values linearly with the base band signal. The envelope of the modulating wave has the same shape as the base band signal provided the following two requirements are satisfied.
1. The carrier frequency fc must be much greater then the highest frequency components fm of the message signal m (t) i.e. fc >> fm
2. The modulation index must be less than unity. if the modulation index is greater than unity, the carrier wave becomes over modulated.
3. Modulation index = (A-B)/(A+B). where A and B as shown in the figure below.
Figure 1: Designing modulation index Fig2: Amplitude modulation model graph
Design Procedure :
Modulated Signal (Under Modulation) :
Given VC = 300mV, fc = 500 KHz, fm = 1KHz.
Set modulating voltage Vm = 200mV.
Emax = 220 V, Emin = 60 V Modulation index (m) = E max - E min/ E max + Emin X 100 = 0.57%
Modulated Signal (Over Modulation) :
Given VC = 300mV, fc = 500 KHz, fm = 1KHz.
Set modulating voltage Vm = 200mV.
Emax = 320 V, Emin = 70 V Modulation index (m) = E max - E min/ E max + Emin X 100 = 1.56%
Test Procedure :
1. The power supply is connected to the collector of the Transistor.
2. Modulated Output is taken from the collector of the Transistor.
3. Calculate Emax and Emin from the output waveform.
AMPLITUDE DEMODULATION :
The