Modulation and Demodulation

A message carrying signal is the one that has to get transmitted over a certain distance, and for it to establish a reliable communication, it requires the help of a high-frequency signal, which should not affect the original properties or characteristics of the transmitted message signal.

If the characteristics of the message signal are changed, then the message contained in it also alters. Therefore, it is essential to take care of the transmitted message signal. A high-frequency signal can travel up to a larger distance, that too, without getting affected by external disturbances. We usually take the help of such a high-frequency signal called a carrier signal for transmitting the message signal. The process is known as Modulation.

Modulation refers to the process of changing the parameters of the carrier signal corresponding to the instantaneous values of the modulating signal.

 

What is a Baseband Signal?

A baseband signal refers to a transmission signal that hasn’t been modulated or demodulated to its original frequency. It can be transmitted over optical fibres, coaxial cables. 

 

What is the Need for Modulation?

The baseband signals are not compatible with direct transmission. For such a signal to travel much larger and longer distances, its strength has to be increased by modulating with a high-frequency carrier wave, which doesn't affect the parameters of the modulating signal.

 

Advantages of Modulation

Before the concept of modulation, the antenna used for transmission had to be large enough. Consequently, the range of communication used to get limited as the wave couldn't travel to a distance without getting distorted.

The advantages of implementing modulation in the communication systems are as follows:

  • The size of the antenna gets reduced

  • There’s no scope for signal mixing

  • The communication range increases

  • Multiplexing of signals occurs

  • Adjustments in the bandwidth are allowed

  • Improvement in the reception quality

 

What are the Different Types of Modulation?

There are several different types of modulations. Based on the modulation techniques used, they are categorized into the types, as shown in the following figure.

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Modulation is broadly classified into continuous-wave modulation and pulse modulation.

In the continuous-wave modulation, a high-frequency sine wave is used as a carrier wave, whereas, in Pulse modulation, a periodic sequence of rectangular pulses is used as a carrier wave.

 

Amplitude Modulation

If the amplitude of the high-frequency carrier wave is varied following the instantaneous amplitude of the modulating signal, it is known as Amplitude Modulation.

If the angle of the carrier wave is varied, following the instantaneous value of the modulating signal, it is known as Angle Modulation.

The angle modulation is further classified into frequency and phase modulation.

 

Frequency Modulation

If the frequency of the carrier wave is varied, following the instantaneous value of the modulating signal, it is known as Frequency Modulation.

 

Phase Modulation

If the phase of the high-frequency carrier wave is varied following the instantaneous value of the modulating signal, it is known as Phase Modulation.

 

Difference Between Modulation and Demodulation

 Modulation is defined as the process of mixing a signal with a sinusoid to produce a new signal. The new signal has quite a few benefits over an un-modulated signal. To be specific, the mixing of the low-frequency signal with the high-frequency carrier signal is known as modulation.

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The term Demodulation refers to the process of extracting the original information-bearing transmitted signal from a carrier wave. A demodulator is an electronic circuit, which is used to recover the information content from the modulated carrier wave.

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