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HDTV Glossary
http://www.hdtvmagazine.com/glossary.php?range=p-r
QAM (digital cable tuners) - Quadrature Amplitude Modulation. Digital modulation technique that calls for 64 and 256 QAM; using 64 QAM a cable channel that today carries one analog video channel could carry 27 Mbps of information, or enough for multiple video programs; using the 256 QAM, the standard 6 MHz cable channel would carry 40 Mbps. See DTV tuners.