We can modulate the information-bearing signal into two types namely.These
are called Modulation Techniques.
1. Analog Modulation
2. Digital Modulation
Analog modulation is the process of converting an analog input signal into a
signal that is suitable for RF transmission.
Digital modulation is the process of converting a digital bistream into an analog signal suitable for RF transmission.
Modulation Index
Modulation Index indicates the depth of modulation. As the amplitude of the modulating signal increases, modulation index increases. For amplitude modulation, the modulation index is given as
m =EmEc
m =Amplitude of modulating signal Amplitude of the carrier.
For frequency modulation,
m =δfm m =Maximum frequency deviation Modulating frequency.
Analog modulation
The Analog carrier signal is modulated by analog information signal so that information bearing analog signal can travel larger distance without the fear of loss due to absorption.
The Analog modulation is of two types:
1) Amplitude Modulation
2) Angle Modulation
The Angle modulation is further classified as Frequency modulation and Phase Modulation.
Amplitude Modulation:
In this type of modulation, the strength of the carrier signal is varied with the modulating signal.
Frequency Modulation: In this type of modulation, the frequency of the carrier signal is varied with the modulating signal.
Phase Modulation: In this type of modulation, the phase of the carrier signal is varied with the modulating signal. It is the variant of the frequency modulation.
The analog carrier signal is modulated by digital information signal. It is also considered as digital to analog conversion.