Q.Mention the basic methods of modulation.

A message signal is superimposed on a high-frequency carrier wave by varying its amplitude, frequency, or phase — giving the three basic types of modulation, AM, FM and PM.

Modulation is the process of superimposing a low-frequency message (information) signal on a high-frequency carrier wave, so that the resulting modulated signal can be transmitted efficiently over long distances using practically-sized antennas. Depending on which characteristic of the carrier wave $c(t) = A_c\sin(\omega_c t + \phi)$ is varied in accordance with the message signal, modulation is of three basic kinds:

1. Amplitude Modulation (AM) — the amplitude $A_c$ of the carrier wave is varied in proportion to the instantaneous amplitude of the message signal, while its frequency and phase remain constant.
2. Frequency Modulation (FM) — the frequency $\omega_c$ of the carrier wave is varied in proportion to the message signal's amplitude, while the amplitude and phase remain constant. …

Modulation = impressing a low-frequency information signal onto a high-frequency carrier by changing the carrier's amplitude, frequency or phase. The three types are AM, FM and PM.

Definition: Modulation is the process of combining a low-frequency information (message) signal with a high-frequency carrier wave, by varying some characteristic of the carrier in accordance with the instantaneous value of the message signal. It is needed because low-frequency audio signals cannot be transmitted efficiently over long distances (they require huge antennas and radiate very little power); a high-frequency carrier makes efficient, long-range transmission possible.

Types of modulation — according to which property of the carrier is varied:

1. Amplitude Modulation (AM) — the amplitude of the carrier is varied in step with the message signal (its frequency and phase stay constant). …

Modulation superimposes a low-frequency message (audio) signal onto a high-frequency carrier wave; the three basic methods vary the carrier's amplitude, frequency, or phase respectively.

Modulation is the process of superimposing a low-frequency message (baseband) signal on a high-frequency carrier wave, so that the resulting signal can be transmitted efficiently over long distances using practically-sized antennas. Depending on which characteristic of the carrier wave is varied in accordance with the message signal, there are three basic methods:

1. Amplitude Modulation (AM): the amplitude of the carrier wave is varied in proportion to the instantaneous amplitude of the message signal, while its frequency and phase remain constant.

2. Frequency Modulation (FM): the frequency of the carrier wave is varied in proportion to the instantaneous amplitude of the message signal, while its amplitude remains constant. FM offers better noise immunity than AM.

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Message signals are impressed onto a high-frequency carrier wave by varying one of its three parameters — amplitude, frequency, or phase — giving Amplitude Modulation, Frequency Modulation, and Phase Modulation respectively.

In communication systems, a low-frequency message (baseband) signal cannot itself be transmitted efficiently over long distances, so it is superimposed on a high-frequency carrier wave through a process called modulation. A sinusoidal carrier $c(t) = A_c \sin(\omega_c t + \phi)$ has three characteristics that can be varied in step with the message signal, giving the three basic methods:

1. Amplitude Modulation (AM): the amplitude $A_c$ of the carrier is varied in proportion to the instantaneous amplitude of the message signal, while its frequency and phase stay constant.
2. Frequency Modulation (FM): the frequency $\omega_c$ of the carrier is varied in proportion to the message signal, while amplitude stays constant. FM is more noise-resistant than AM. …

Modulation is done by varying either the amplitude, frequency, or phase of a carrier wave in step with the message signal, giving AM, FM and PM respectively.

Modulation is the process of superimposing a low-frequency message (information/baseband) signal onto a high-frequency carrier wave, so that the signal can be efficiently transmitted over long distances. Since a sinusoidal carrier wave $c(t) = A_c \sin(\omega_c t + \phi)$ has three characteristic parameters — amplitude $A_c$, angular frequency $\omega_c$, and phase $\phi$ — modulation can be achieved by varying any one of these in proportion to the instantaneous value of the message signal. This gives the three basic methods of (analog) modulation:

1. Amplitude Modulation (AM): The amplitude of the carrier wave is varied in accordance with the instantaneous amplitude of the message signal, while its frequency and phase remain constant.
2. Frequency Modulation (FM): The frequency of the carrier wave is varied in accordance with the message signal, while its amplitude remains constant. FM gives better noise immunity than AM. …