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AM

Amplitude Modulation

A modulation technique that varies the amplitude of a carrier wave in proportion to the instantaneous value of the modulating signal while keeping frequency and phase constant
Category: Modulation
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Understanding Amplitude Modulation

AM encodes information by varying the carrier envelope. The modulation index (m) defines the ratio of the modulating signal amplitude to the carrier amplitude. At m=1 (100% modulation), the carrier amplitude varies from zero to twice its unmodulated value.

Standard AM produces a carrier and two sidebands (upper and lower), with the carrier containing no information. Single-sideband (SSB) and double-sideband suppressed carrier (DSB-SC) are bandwidth-efficient variants that eliminate the redundant carrier and/or sideband.

Common Questions

Frequently Asked Questions

Why is AM less efficient than FM?

Standard AM wastes power in the carrier (which carries no information) and is susceptible to amplitude noise. At 100% modulation, only 1/3 of total power is in the sidebands.

What is the bandwidth of an AM signal?

Standard AM bandwidth is twice the highest modulating frequency, as upper and lower sidebands are mirror images of each other.

See Also

Related Terms

AM → FM → Modulation →
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