Glossary Definition for Quadrature-Amplitude-Modulation

Glossary Term: Quadrature-Amplitude-Modulation 

Definition

Quadrature Amplitude Modulation: A modulation method in which two signals are used to amplitude-modulate two carriers that are in quadrature (90 degrees out of phase with each other). The two modulated signals are combined.

A common application is in PAL and NTSC color television transmission. Color is encoded into two analog signals (called I and Q), which modulate quadrature color carriers.

Modems also use this approach, to increase the data bandwidth they can carry (or, more accurately, to trade bandwidth for error rate or noise immunity).

Synonyms
  • Quadrature Amplitude Modulation
  • Quadrature Modulation
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