Explain Modulation techniques.
1. Amplitude modulation - AM
2. Angle Modulation
A. Frequency modulation - FM
B. Phase modulation - PM
1. Amplitude Modulation – AM
A continuous-wave goes on continuously without any intervals and it is the baseband message signal, which contains the information. This wave has to be modulated.
According to the standard definition, “The amplitude of the carrier signal varies in accordance with the instantaneous amplitude of the modulating signal.”
Means that the amplitude of the carrier signal containing no information varies as per the amplitude of the signal containing information, at each instant.
This can be well explained by the following figure.
Fig. Amplitude Modulation
The figure shows the modulating wave, which is the message signal.
The next one is the carrier wave, which is a high frequency signal and contains no information. While, the last one is the resultant modulated wave.
2. Angle Modulation
Angle modulation is further divided into frequency modulation and phase modulation.
A. Frequency Modulation(FM)
In amplitude modulation, the amplitude of the carrier signal varies. Whereas, in Frequency Modulation (FM), the frequency of the carrier signal varies in accordance with the instantaneous amplitude of the modulating signal.
Hence, in frequency modulation, the amplitude and the phase of the carrier signal remains constant. This can be better understood by observing the following figure.
Fig. Frequency Modulation
The frequency of the modulated wave increases, when the amplitude of the modulating or message signal increases.
Similarly, the frequency of the modulated wave decreases, when the amplitude of the modulating signal decreases.
Note that, the frequency of the modulated wave remains constant and it is equal to the frequency of the carrier signal, when the amplitude of the modulating signal is zero.
B. Phase Modulation(PM)
In frequency modulation, the frequency of the carrier varies. Whereas, in Phase Modulation (PM), the phase of the carrier signal varies in accordance with the instantaneous amplitude of the modulating signal.
So, in phase modulation, the amplitude and the frequency of the carrier signal remains constant.
This can be better understood by observing the following figure.
Fig. Phase Modulation
The phase of the modulated wave has got infinite points, where the phase shift in a wave can take place.
The instantaneous amplitude of the modulating signal changes the phase of the carrier signal.
When the amplitude is positive, the phase changes in one direction and if the amplitude is negative, the phase changes in the opposite direction.
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