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What is need of modulation?

Subject : Principle of Communication Engineering

Topic : Introduction to Electronic Communication

Difficulty : Low

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34views

Need for modulation:

The baseband signals can be transmitted directly, but the baseband transmission has many limitations which can be overcome using modulation.

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.

The modulation process has the following advantages:

• Reduction in the height of antenna:

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

For the transmission of radio signals, the antenna height must be a multiple of (λ/4).Here λ is the wavelength. Λ =c/f where c is velocity of light and 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:

Minimum antenna height= λ/4 = c/4f=(3* 108)/(410103 )=7500meters i.e. 7.5 km

It is impossible to build antennae this big.

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

Minimum antenna height= λ/4 = c/4f=(3108)/(410*106 )=75 meter

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.

-Avoids mixing of 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 friends 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.

-Increase the range of 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.

-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.

-Improves quality of reception:

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

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21views

Need for modulation:

• The baseband signals can be transmitted directly, but the baseband transmission has many limitations which can be overcome using modulation.
• 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.
• The modulation process has the following advantages:

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

For the transmission of radio signals, the antenna height must be a multiple of (λ/4).Here λ is the wavelength. Λ =c/f where c is velocity of light and 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:

Minimum antenna height= λ/4 = c/4f=(3* 108)/(410103 )=7500meters i.e. 7.5 km

It is impossible to build antennae this big.

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

Minimum antenna height= λ/4 = c/4f=(3108)/(410*106 )=75 meter

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.

-Avoids mixing of signal

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 friends 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.

-Increase the range of 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.

-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.

-Improves quality of reception:

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