AM (Amplitude Modulation) - definition
AM (Amplitude Modulation) - definition
AM (Amplitude Modulation) is a classical method of analog modulation in which the amplitude of a carrier wave is varied in proportion to the instantaneous value of the information signal. The carrier wave, characterized by a constant frequency and phase, serves as the data carrier, while the information—such as audio—affects only its amplitude. As a result, the modulated signal’s envelope mirrors the shape of the modulating signal, allowing the original information to be recovered during demodulation.
AM has been widely used in radio communications, particularly within the medium and shortwave frequency bands, where the simplicity of transmitter and receiver design was a major advantage. The key benefits of amplitude modulation include ease of implementation and compatibility with simple detection circuits that can operate without an external power source. AM signals can be transmitted over long distances; however, their susceptibility to noise and interference—directly affecting the amplitude—limits transmission quality.
An AM signal consists of the carrier wave and two symmetrical sidebands that carry the actual information. In conventional AM, the entire signal structure is transmitted, which reduces energy efficiency and requires a broad transmission bandwidth. To address these limitations, more advanced forms such as Single Sideband (SSB) and reduced-carrier modulation were developed, improving spectral and power efficiency.
Although modern radio systems predominantly use digital modulation techniques or more robust analog methods, AM remains a relevant topic in technical education and continues to be employed in specialized applications such as aeronautical communication and international shortwave broadcasting.
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