Amplitude Modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. In AM, the amplitude of the carrier wave is varied in proportion to that of the message signal, such as an audio signal. This allows the signal to be encoded and transmitted over long distances.
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A common real-life example of amplitude modulation is AM radio broadcasting. In this system, radio stations encode sound signals onto a high-frequency carrier wave, which is then transmitted through the air. When you tune your AM radio to a specific frequency, the radio receiver demodulates the signal, extracting the audio content so you can hear the broadcast.
The process of changing the amplitude of a carrier wave in accordance with the amplitude of the audio frequency (AF) signal is known as amplitude modulation (AM). Carrier wave remains unchanged in AM frequency. The amplitude of a modulated wave is varied in accordance with the amplitude of the modulating wave.
The ratio of change of amplitude of the carrier wave to the amplitude of the original carrier wave is called the modulation factor or degree of modulation or modulation index (m).
If a carrier wave is modulated by several sine waves the total modulated index m is given by
Suppose voltage equations for carrier wave and modulating wave are
where,
The voltage equation for AM wave is
The above AM wave indicated that the AM wave is equivalent to the summation of three sinusoidal waves, one having amplitude 'E' and the other two having amplitude
The AM wave contains three frequencies,
In general sideband frequencies are close to the carrier frequency.
The two sidebands lie on either side of the carrier frequency at equal frequency interval fm.
So, bandwidth
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Solved Example Based On Amplitude Modulation
Example 1: Choose the correct statement :
1) In amplitude modulation the amplitude of the high frequency carrier wave is made to vary in proportion to the amplitude of the audio signal.
2)In amplitude modulation, the frequency of the high-frequency carrier wave is made to vary in proportion to the amplitude of the audio signal
3)In frequency modulation the amplitude of the high frequency carrier wave is made to vary in proportion to the amplitude of the audio signal.
4)In frequency modulation, the amplitude of the high-frequency carrier wave is made to vary in proportion to the frequency of the audio signal
Solution:
The amplitude of a modulated wave is varied in accordance with the amplitude of the modulating wave
In amplitude modulation, the amplitude of the high-frequency carrier wave is made to vary in proportion to the amplitude of the audio signal.
Hence, the correct answer is the option (1).
Example 2: A signal
1)
2)
3)
4) NoneSolution:
Amplitude modulated signal
therefore
The AM signal is given by
Hence, the correct answer is the option (1).
Example 3: A 100 V carrier wave is made to vary between 160 V and 40 V by a modulating signal. What is the modulation index?
1) 0.6
2) 0.5
3) 0.4
4) 0.3
Solution:
From (1) \& (2)
So,
Hence, the correct answer is the option (1).
Example 4: An amplitude-modulated signal is plotted below :
Which one of the following best describes the above signal?
1)
2)
3)
4)
Solution:
Voltage equation for AM wave -
Resultant Modulated wave
From the graph
and
So signal equation is
Hence, the correct answer is the option (4).
Example 5: An audio signal
1) 25
2) 40
3) 15
4) 50
Solution:
The percentage change in the modulated wave and the carrier wave is given by :
Hence, the correct answer is the option (1).
Amplitude Modulation (AM) is a communication technique where the amplitude of a high-frequency carrier wave is varied in proportion to the amplitude of an audio signal. This method is widely used in AM radio broadcasting, where sound signals are encoded onto a carrier wave for transmission and later demodulated by receivers. Key concepts in AM include modulation index, sideband frequencies, and bandwidth, which determine the efficiency and clarity of the transmitted signal.
A vector in physics is a quantity that has both magnitude and direction, represented by an arrow.
A unit vector is a vector with a magnitude of one. It indicates direction only.
Vectors can be multiplied in several ways: scalar multiplication (multiplying a vector by a scalar quantity), dot product (or scalar product, yielding a scalar), and cross product (or vector product, yielding another vector).
Vector components are used to simplify vector calculations, especially in coordinate systems like Cartesian coordinates. They break down a vector into its perpendicular components along the coordinate axes (x, y, z).
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