Modulation is a processes of the characteristics of carrier signals superimposed by message signal.
The process of superimposition of modulating signal (low frequency) over carrier wave(high frequency )
is called modulation.
The process of impressing low-frequency information to be transmitted on to a high-
frequency wave, called the carrier wave, by changing the characteristics of either its
amplitude, frequency or phase angle is called modulation.
Another definition for modulation is:
The process of altering the characteristics of the amplitude, frequency, or phase angle
of the high-frequency signal in accordance with the instantaneous value of the
modulating wave is called modulation.
Functions of the Carrier Wave
The main function of the carrier wave is to carry the audio or video signal from the
transmitter to the receiver. The wave that is resulted due to superimposition of audio
signal and carrier wave is called the modulated wave.
Need for Modulation
The reason why low-frequency signals cannot be transmitted over long distances
through space is listed below:
1. Short Operating Range – When a wave has a large frequency, the energy
associated with it will also be large. Thus low-frequency signals have less power
that does not enable them to travel over long distances.
2. Poor Radiation Efficiency – The radiation efficiency becomes very poor for low-
frequency signals.
3. Mutual Interference – If all audio frequencies are sent continuously from different
sources, they would all get mixed up and cause erroneous interference air. If
modulation is done, each signal will occupy different frequency levels and can be
transmitted simultaneously without any error.
4. Huge Antenna Requirement – For a effective signal transmission, the sending
and receiving antenna should be at least 1/4th of the wavelength of the signal.
Thus, for small frequencies, the antenna will have kilometres of length. But if the
signal has the range of MegaHertz frequency, then the antenna size would be
less. The carrier wave cannot be used alone for transmission purposes. Since its
amplitude, frequency, and phase angle are constant with respect to some
preference.
, Need for Modulation
In modulation technique, the message signal frequency is raised to a range so that it is more
useful for transmission. The following points describe modulation’s importance in
communication system.
In signal transmission, the signals from various sources are transmitted through a common
channel simultaneously by using multiplexers. If these signals are transmitted simultaneously
with certain bandwidth, they cause interference. To overcome this, speech signals are
modulated to various carrier frequencies in order for the receiver to tune them to desired
bandwidth of his own choice within the range of transmission.
Another technical reason is antenna size; the antenna size is inversely proportional to the
frequency of the radiated signal. The order of the antenna aperture size is at least one by tenth
of the wavelength of the signal. Its size is not practicable if the signal is 5 KHz; therefore, raising
frequency by modulating process will certainly reduce the height of the antenna.
Modulation is important to transfer the signals over large distances, since it is not possible to
send low-frequency signals for longer distances.
Similarly, modulation is also important to allocate more channels for users and to increase noise
immunity.
Types of Modulation
The sinusoidal carrier wave can be given by the equation
vc = Vc Sin(wct + θ) = Vc Sin(2fct + θ)
Vc – Maximum Value
fc – Frequency
θ – Phase Relation
Since the three variables are the amplitude, frequency, and phase angle, the
modulation can be done by varying any one of them. Thus there are three modulation
types namely:
Amplitude Modulation (AM)
Frequency Modulation (FM)
Phase Modulation (PM)
,Click on the links given above to know more.
In India, radio broadcasting is done through amplitude modulation. Television
broadcasting is done with amplitude modulation for video signals and frequency
modulation for audio signals.
Amplitude Modulation (AM)
Definition
The method of varying amplitude of a high-frequency carrier wave in accordance with the information
to be transmitted, keeping the frequency and phase of the carrier wave unchanged is called Amplitude
Modulation. The information is considered as the modulating signal and it is superimposed on the
carrier wave by applying both of them to the modulator. The detailed diagram showing the amplitude
modulation process is given below.
, Amplitude Modulation
As shown above, the carrier wave has positive and negative half cycles. Both these cycles are varied
according to the information to be sent. The carrier then consists of sine waves whose amplitudes follow
the amplitude variations of the modulating wave. The carrier is kept in an envelope formed by the
modulating wave. From the figure, you can also see that the amplitude variation of the high-frequency
carrier is at the signal frequency and the frequency of the carrier wave is the same as the frequency of
the resulting wave.
Analysis of Amplitude Modulation Carrier Wave
1. Carrier wave →
2. Modulating signal →
The process of superimposition of modulating signal (low frequency) over carrier wave(high frequency )
is called modulation.
The process of impressing low-frequency information to be transmitted on to a high-
frequency wave, called the carrier wave, by changing the characteristics of either its
amplitude, frequency or phase angle is called modulation.
Another definition for modulation is:
The process of altering the characteristics of the amplitude, frequency, or phase angle
of the high-frequency signal in accordance with the instantaneous value of the
modulating wave is called modulation.
Functions of the Carrier Wave
The main function of the carrier wave is to carry the audio or video signal from the
transmitter to the receiver. The wave that is resulted due to superimposition of audio
signal and carrier wave is called the modulated wave.
Need for Modulation
The reason why low-frequency signals cannot be transmitted over long distances
through space is listed below:
1. Short Operating Range – When a wave has a large frequency, the energy
associated with it will also be large. Thus low-frequency signals have less power
that does not enable them to travel over long distances.
2. Poor Radiation Efficiency – The radiation efficiency becomes very poor for low-
frequency signals.
3. Mutual Interference – If all audio frequencies are sent continuously from different
sources, they would all get mixed up and cause erroneous interference air. If
modulation is done, each signal will occupy different frequency levels and can be
transmitted simultaneously without any error.
4. Huge Antenna Requirement – For a effective signal transmission, the sending
and receiving antenna should be at least 1/4th of the wavelength of the signal.
Thus, for small frequencies, the antenna will have kilometres of length. But if the
signal has the range of MegaHertz frequency, then the antenna size would be
less. The carrier wave cannot be used alone for transmission purposes. Since its
amplitude, frequency, and phase angle are constant with respect to some
preference.
, Need for Modulation
In modulation technique, the message signal frequency is raised to a range so that it is more
useful for transmission. The following points describe modulation’s importance in
communication system.
In signal transmission, the signals from various sources are transmitted through a common
channel simultaneously by using multiplexers. If these signals are transmitted simultaneously
with certain bandwidth, they cause interference. To overcome this, speech signals are
modulated to various carrier frequencies in order for the receiver to tune them to desired
bandwidth of his own choice within the range of transmission.
Another technical reason is antenna size; the antenna size is inversely proportional to the
frequency of the radiated signal. The order of the antenna aperture size is at least one by tenth
of the wavelength of the signal. Its size is not practicable if the signal is 5 KHz; therefore, raising
frequency by modulating process will certainly reduce the height of the antenna.
Modulation is important to transfer the signals over large distances, since it is not possible to
send low-frequency signals for longer distances.
Similarly, modulation is also important to allocate more channels for users and to increase noise
immunity.
Types of Modulation
The sinusoidal carrier wave can be given by the equation
vc = Vc Sin(wct + θ) = Vc Sin(2fct + θ)
Vc – Maximum Value
fc – Frequency
θ – Phase Relation
Since the three variables are the amplitude, frequency, and phase angle, the
modulation can be done by varying any one of them. Thus there are three modulation
types namely:
Amplitude Modulation (AM)
Frequency Modulation (FM)
Phase Modulation (PM)
,Click on the links given above to know more.
In India, radio broadcasting is done through amplitude modulation. Television
broadcasting is done with amplitude modulation for video signals and frequency
modulation for audio signals.
Amplitude Modulation (AM)
Definition
The method of varying amplitude of a high-frequency carrier wave in accordance with the information
to be transmitted, keeping the frequency and phase of the carrier wave unchanged is called Amplitude
Modulation. The information is considered as the modulating signal and it is superimposed on the
carrier wave by applying both of them to the modulator. The detailed diagram showing the amplitude
modulation process is given below.
, Amplitude Modulation
As shown above, the carrier wave has positive and negative half cycles. Both these cycles are varied
according to the information to be sent. The carrier then consists of sine waves whose amplitudes follow
the amplitude variations of the modulating wave. The carrier is kept in an envelope formed by the
modulating wave. From the figure, you can also see that the amplitude variation of the high-frequency
carrier is at the signal frequency and the frequency of the carrier wave is the same as the frequency of
the resulting wave.
Analysis of Amplitude Modulation Carrier Wave
1. Carrier wave →
2. Modulating signal →
