Explain the need for modulation in a communication system |

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23.05.2019 10:16:11 - In the modulation process, some parameter of the carrier wave (such as amplitude, frequency or phase) is varied in accordance with the modulating signal .

( - Modulation

In the modulation process, two signals are used namely the modulating signal and the carrier.

The modulating signal is nothing but the baseband signal or information signal while the carrier is a high frequency sinusoidal signal.

In the modulation process, some parameter of the carrier wave (such as amplitude, frequency or phase) is varied in accordance with the modulating signal . This


modulated signal is then transmitted by the transmitter.

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The receiver demodulates the received modulated signal and gets the original information signal back.

Thus, demodulation is exactly opposite to modulation.

In the process of modulation the carrier wave actually acts as carrier which carries the information signal from the transmitter to receiver.

Need of Modulation

You may be ask, when the baseband signal can be transmitted directly why to use the modulation?

The answer is that the baseband transmission has many limitations which can be overcome using modulation. It is explained below.

In the process of modulation, the baseband signal is translated i.e., shifted from low frequency to high frequency. This frequency shift is proportional to the frequency of carrier.

Advantages of Modulation

1. Reduction in the height of antenna

2. Avoids mixing of signals

3. Increases the range of communication

4. Multiplexing is possible

5. Improves quality of reception

We will discuss each of these advantages in detail below.

1. Reduction in the height of antenna

For the transmission of radio signals, the antenna height must be multiple of λ/4, where λ is the wavelength.

λ = c /f

Where c: is the velocity of light

F: is the frequency of the signal to be transmitted

The minimum antenna height required to transmit a baseband signal of f = 10 kHz is calculated as follows:

The antenna of this height is practically impossible to install.

Now, let us consider a modulated signal at f = 1 MHz. The minimum antenna height is given by,

This antenna can be easily installed practically. Thus, modulation reduces the height of the antenna.

2. Avoids mixing of signals

If the baseband sound signals are transmitted without using the modulation by more than one transmitter, then all the signals will be in the same frequency range i.e. 0 to 20 kHz. Therefore, all the signals get mixed together and a receiver cannot separate them from each other.

Hence, if each baseband sound signal is used to modulate a different carrier then they will occupy different slots in the frequency domain (different channels). Thus, modulation avoids mixing of signals.

3. Increase the Range of Communication

The frequency of baseband signal is low, and the low frequency signals cannot travel long distance when they are transmitted. They get heavily attenuated.

The attenuation reduces with increase in frequency of the transmitted signal, and they travel longer distance.

The modulation process increases the frequency of the signal to be transmitted. Therefore, it increases the range of communication.

4. Multiplexing is possible

Multiplexing is a process in which two or more signals can be transmitted over the same communication channel simultaneously.

This is possible only with modulation.

The multiplexing allows the same channel to be used by many signals. Hence, many TV channels can use the same frequency range, without getting mixed with each other or different frequency signals can be transmitted at the same time.

5. Improves Quality of Reception

With frequency modulation (FM) and the digital communication techniques such as PCM, the effect of noise is reduced to a great extent. This improves quality of reception.

Established in 2000, the main products are modulators both in analog and digital ones, amplifier and combiner. We are the very first one in manufacturing the headend system in China. Our 16 in 1 and 24 in 1 now are the most popular products all over the world.

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Dingshengwei Electronics Co., Ltd

Company Address: Buliding A,the first industry park of Guanlong,Xili Town,Nanshan,Shenzhen,Guangdong,China

Tel : +86 0755 26909863

Fax : +86 0755 26984949

Phone: +86 13410066011

Skype: soukaken

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