Amplitude modulation

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Telefunken arc radiotelephone

Meissner radiotelephone transmitter

Illustration of Amplitude Modulation

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AM spectrum

AM signal

Amplitude Modulation

Amplitude Modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength (amplitude) of the carrier wave in proportion to the waveform being sent, such as an audio signal.

History

The development of amplitude modulation dates back to the early 20th century. It was first used for voice transmission in radio broadcasting and later for television and other forms of communication.

Principle of Operation

In amplitude modulation, the amplitude of the carrier wave is varied in accordance with the information signal. The carrier wave itself remains at a constant frequency. The modulated signal consists of the carrier frequency and two sidebands, which are the sum and difference of the carrier frequency and the modulating signal frequency.

Mathematical Representation

The mathematical representation of an AM signal can be expressed as: \[ s(t) = [A + m(t)] \cos(2 \pi f_c t) \] where:

• \( s(t) \) is the modulated signal
• \( A \) is the amplitude of the carrier wave
• \( m(t) \) is the message signal
• \( f_c \) is the carrier frequency

Types of Amplitude Modulation

There are several types of amplitude modulation, including:

• Double-sideband suppressed-carrier transmission (DSB-SC)
• Single-sideband modulation (SSB)
• Vestigial sideband modulation (VSB)
• Quadrature amplitude modulation (QAM)

Applications

Amplitude modulation is widely used in various applications, including:

• AM radio broadcasting
• Aviation communication
• Two-way radio communication
• Television broadcasting (in the form of VSB)

Advantages and Disadvantages

Advantages

• Simplicity of implementation
• Compatibility with existing radio receivers

Disadvantages

• Susceptibility to noise and interference
• Inefficient use of bandwidth

See Also

• Frequency modulation
• Phase modulation
• Modulation
• Demodulation
• Radio broadcasting
• Telecommunication

Related Pages

• Radio wave
• Carrier wave
• Sideband
• Signal processing
• Analog signal