QAM (Quadrature amplitude modulation)

A digital modulation format which is used for the transmission downward in cable TV systems - commonly used for cable HDTV. A QAM tuner will allow you to see digital cable channels without a cable box but only those that are broadcast without restriction. For example, a 600 baud line (600 shifts in the signal per second) can effectively transmit 2,400 bit/s using the technique.

Televisions and other products equipped with QAM tuners can tune unscrambled digital cable channels from some cable providers, but to view scrambled channels a CableCard is required.

Many new televisions and other products equipped with QAM tuners so that users are not require to have a set top box in order to receive digital cable. However, most content sent by the cable company is scrambled, with the exception of some local channels. Which channels are scrambled is subject to change and varies by cable company and geographic location. Most consumers will still need a set top box to unscramble the digital cable signal to receive most cable channels.

QAM tuning for unencrypted (local must-carry) stations generally in High-Definition. With a deployment of recording capable DVR (Digital Video Recorder) set-tops, the industry makes the fastest inroads into the average US home.  The DVRs are necessary for recording and storing premium pay channels that are encrypted and cannot easily be imported to other players. 

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