Modulation and the need for Modulation

What is Modulation?

Transmission of information by the communication systems over large distances is quite a feat of human ingenuity. We can talk, video chat and text anyone on this planet! Communication systems has used a very clever technique called Modulation to increase the reach of the signals. Two signals are involved in the modulation process. Message signals also known as baseband signals. Baseband signals are the band of frequencies representing the original signal. This is the signal to be transmitted to the receiver. The frequency of such a signal is usually low. The other signal involved with this is a high-frequency sinusoidal wave. This signal is called the carrier signal. The frequency of the carrier signals is almost, always higher than that of the baseband signal. The amplitude of the baseband signal is transferred to the high-frequency carrier. Such a higher frequency carrier wave is able to travel much farther than the baseband signal. But that’s not the only advantage of modulation.

What is the need for modulation?

  1. Size of the Antennae

When the transmission occurs over free space, the antennae radiate the signal out and the receiver receives it. In order to operate efficiently, antennae need to be in order of the magnitude of the wavelength of the transmitted signal.

\(L = \lambda = \frac{u}{\vartheta } = \frac{(3*10^{8})}{\vartheta }{Hz}\)

Speech frequencies range from 20 Hz to 20 kHz. So supposing this is a frequency of 20 kHz and it is radiated out to a receiver through a channel of free space.

\(Length \;of \;Antennae = \frac{3*10^{8}}{20*10^{3}} = 15000 m = 15 km\)

It is impossible to build an antenna this big. Instead, we use the concept of using a high-frequency carrier wave for the transfer of the signal and thus, use a 1000 kHz carrier wave to carry the signal. Length of the antennae now would be;

\(Length\; of\; Antennae = \frac{3*10^{8}}{1000*10^{3}} = 300 m\)

This length of the antenna can be built easily and this example clearly shows us how hugely the process of modulation is enabling communication systems.

  1. Wireless Communication

By using modulation to transmit the signals through space to long distances, we have removed the need for wires in the communication systems. The technique of modulation helped humans to use wireless equipment in a bug way in their lives. Telephones no longer had to remain plugged to a wall. All the benefits of modulation has raised our standards of living in a considerable manner.

  1. Interference from other signals

This is a point from the practical side of things. Suppose you are transmitting the baseband signal as it is to a receiver, say your friend’s phone. Just like you, there will be thousands of people of people in the city using their mobile phones. There is no way to tell such signals apart and they will interfere with each other leading to a lot of noise in the system and a very bad output. By using a carrier wave of high frequencies and allotting a band of frequencies to each message, there is no mixing up of signals and the received signals are absolutely perfect.

There are three types of Modulation:

  • Amplitude Modulation
  • Frequency Modulation
  • Phase Modulation

Learn these important concepts in the next articles only at BYJU’s.


Practise This Question

A ray of light is incident at an angle i from denser to rare medium. The reflected and the refracted rays are mutually perpendicular. The angle of reflection and the angle of refraction are respectively r and r’, then the critical angle will be