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.
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CONTACT US
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Company Address: Buliding A,the first industry park of
Guanlong,Xili Town,Nanshan,Shenzhen,Guangdong,China
Tel : +86 0755 26909863
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Source: electronicspost
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