    Cable QAM for HDTV Tuners Explained 
QAM is short for Quadrature amplitude modulation, which in the Digital TV world, is a scheme for sending TV signals via cable. Basically you are sending two signals down a single path, thereby doubling the bandwidth. This is important to the cable companies since they have limited bandwidth and HDTV takes quite a bit more of it than standard definition broadcasts. It come in two flavors in the US, 64 and 256 QAM. QAM64 is typically used for the cable music channels, and other standard definition stations. QAM256 is used primarily for High Definition signals. Both QAM64 and QAM256 will put a number of subchannels on the one channel number. In the case of QAM64 they could put 40 subchannels on one channel. QAM256 typically has only 2 subchannels, although some cable companies have been known to use 3. The more subchannels used, the less bandwidth for each individual station. The bottom line from the HDTV PC tuner perspective is you can receive unencrypted HDTV cable channels with certain tuners. QAM tuning is not well supported by the cable companies, as they would probably prefer that you rent one of their digital cable boxes instead. However, it is kosher to get the unencrypted channels since they are usually the local ones you can receive with an over-the-air antenna. These unencrypted channels can usually be found even on “basic” cable service. So if you want to receive your HDTV via cable, get a tuner that supports QAM. Go here for the current list of QAM capable HDTV PC tuners. Before you invest in a QAM tuner and local cable, check the AVS Forum (here) for information on the unencrypted channels provided by your local cable company. You’ll have to search the forum threads for your town/area and then browse the posts for that information. NOTE: Even if you pay for the “premium” HDTV cable channels, you will NOT be able to receive them through your PC HDTV tuner as HDTV. Only the cable company’s digital box is equipped to decode the encrypted channels.
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