Modulation
In the modulation process (includes the digital modulator and analog modulator) , 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.
The receiver demodultes the received modulated signal and
gets the original information signal back.
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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
Company: Dingshengwei
Electronics Co., Ltd
Address: Bldg 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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