QAM (television)

Digital television standard QAM is a digital television standard using quadrature amplitude modulation. It is the format by which digital cable channels are encoded and transmitted via cable television providers. QAM is used in a variety of communications systems such as Dial-up modems and Wi-Fi. In cable systems, a QAM tuner is linked to the cable in a manner that is equivalent to an ATSC tuner which is required to receive over-the-air (OTA) digital channels broadcast by local television stations when attached to an antenna. Most new HDTV digital televisions support both of these standards. QAM uses the same 6 MHz bandwidth as ATSC, using a standard known as ITU-T Recommendation J.83 Annex B ("J.83b"). Technical details QAM is a modulation format and does not specify the format of the digital data being carried. However, when used in the context of US digital cable television, the format of the data transmitted using this modulation is based on ITU-T J.83 Annex B ("J.83b"). This is in contrast to DVB-C which is also based on QAM modulation, but uses a DVB-based data format which is incompatible with North American receivers. QAM is a parallel form of modulation that transmits two