What is Quadrature Amplitude Modulation or QAM?

Quadrature Amplitude Modulation (QAM) is a highly efficient modulation scheme used to transmit digital data. It operates by modulating the amplitudes of two separate carrier waves that share the exact same frequency but are exactly 90 degrees out of phase with one another. The term 'quadrature' refers to this 90-degree phase difference, often mathematically represented as sine and cosine waves. Because these two carriers are mathematically orthogonal (independent), they can be combined, transmitted, and then perfectly separated at the receiver without interfering with each other, effectively doubling the data capacity. Distractors that mention digital data compression, single sideband generation, or analog video techniques are incorrect. While the phasing method for SSB also uses a 90-degree phase shift, QAM specifically modulates the amplitude of both quadrature carriers to encode dense digital data symbols.