Amplitude Modulation definition:

Amplitude modulation (AM) is a method of transmitting information by varying the amplitude of a carrier wave in response to changes in the amplitude of a modulating signal. In other words, the amplitude of the high-frequency carrier signal is varied in proportion to the amplitude of a lower frequency information signal (the modulating signal) that carries the information to be transmitted.

Amplitude Modulation


The modulating signal is typically an audio signal, which can be the voice of a person, music, or other sounds. The amplitude modulation technique allows the transmission of the original signal over long distances, and the signal can be received and demodulated by a receiver to extract the original information.

AM is one of the simplest forms of modulation, and it is widely used in broadcasting, radio communications, and other applications where the transmission of information is required over long distances.

Amplitude modulation is defined as the process in which the amplitude of the carrier signal is varied in accordance with the modulating signal or message signal.
Consider a sinusoidal carrier signal C (t) is defined as 

Time domain description

In signal processing, the time domain is a representation of a signal as a function of time. This means that the signal is viewed as a series of time-varying values, where the amplitude of the signal changes with time.

In the time domain, the signal is typically represented as a waveform, which shows the amplitude of the signal as a function of time. The waveform can be plotted on a graph where the x-axis represents time and the y-axis represents the amplitude of the signal.

By analyzing the waveform in the time domain, it is possible to extract various characteristics of the signal such as its frequency content, amplitude, duration, and shape. This can be useful in applications such as audio and speech processing, where the signal needs to be analyzed and manipulated in the time domain.

However, in some cases, it may be more convenient or efficient to analyze the signal in the frequency domain, which provides information about the frequency content of the signal rather than its time-varying characteristics.

Percentage modulation or modulation factor

The percentage modulation or modulation factor is a measure of the degree of modulation in an amplitude modulated (AM) signal. It is defined as the ratio of the amplitude of the modulating signal to the amplitude of the carrier signal, expressed as a percentage.

The percentage modulation is calculated using the formula:

% modulation = (amplitude of modulating signal/amplitude of carrier signal) x 100%

For example, if the carrier signal has an amplitude of 10 volts and the modulating signal has an amplitude of 2 volts, the percentage modulation would be:

% modulation = (2/10) x 100% = 20%

This means that the amplitude of the carrier signal is varying by 20% due to the modulation of the modulating signal.

The percentage modulation is an important parameter in AM systems because it affects the efficiency of the transmission and the quality of the recovered signal at the receiver. A higher percentage modulation results in a higher power consumption and may cause distortion or clipping of the signal. On the other hand, a low percentage modulation may result in poor signal quality and reduced intelligibility.

Frequency domain description

In signal processing, the frequency domain is a representation of a signal as a function of frequency. This means that the signal is viewed as a combination of different sinusoidal components, each with a specific frequency and amplitude.

In the frequency domain, the signal is typically represented as a spectrum, which shows the amplitude of each sinusoidal component as a function of frequency. The spectrum can be plotted on a graph where the x-axis represents frequency and the y-axis represents amplitude.

By analyzing the spectrum in the frequency domain, it is possible to extract various characteristics of the signal such as its frequency content, bandwidth, and harmonic components. This can be useful in applications such as audio and image processing, where the signal needs to be analyzed and manipulated based on its frequency components.

The transformation from the time domain to the frequency domain is done using a mathematical tool called the Fourier transform. The Fourier transform converts the signal from its time-domain representation to its frequency-domain representation, allowing the analysis and manipulation of the signal based on its frequency components.

The frequency domain is particularly useful in applications such as audio and image compression, where the signal can be transformed to a more efficient representation based on its frequency content. It is also used in digital signal processing, where signals can be filtered, equalized, or modified based on their frequency components.

Advantages of Amplitude modulation:-

• Generation and detection of AM signals are very easy
• It is very cheap to build, due to this reason it I most commonly used in AM radio broad casting

Disadvantages of Amplitude of modulation:-

• Amplitude modulation is wasteful of power
• Amplitude modulation is wasteful of band width

Application of Amplitude modulation: -

AM Radio Broadcasting