What exactly does a clear qam tuner do?

Question

What exactly does a clear qam tuner do?

Answer 1

In February of 2009, all TV stations will start broadcasting in digital, and you'll need a QAM tuner to receive those channels.  Local HD channels are already being broadcast and are using QAM.  

Cable companies are also carrying these HD channels, so if your HDTV has a QAM tuner and you subscribe to cable, you can get those local HD channels as well.  However, you won't be able to get things like Discovery HD - those channels are encrypted, and you need to either get a set-top box from the cable company, or a cable card (assuming your TV or DVR can support this.)

Those ads you see on TV about getting a new tuner for the switchover in 2009 are actually for a clear QAM tuner - the same as the one included in all new HDTVs and many new non-HD TVs today.

Answer 2

A "clear QAM" tuner is used to demodulate and decode TV stations that are sent over cable TV digitally, but not encrypted.

For example, most basic cable channels would be sent over the cable unencrypted, or at the very least, the local channels would be unencrypted.

For any other digital channels, you'd have to have a set-top box to demodulate, decode and decrypt the channel, unless your TV, TiVo, etc. and cable system supports CableCARDs.

http://en.wikipedia.org/wiki/CableCARD

Edit:  In response to PoohBear.  Your post is mostly right, except those ads for the new tuner for the switch-over in 2009, are not for clear QAM tuners, but rather ATSC tuners for over-the-air broadcasts, which use a different modulation technology than cable - 8VSB vs. cable's QAM.