If you're currently in the market for a high definition television (HDTV) then you've probably have learned that most digital televisions sold today come equipped with three types of tuners: ATSC, NTSC and QAM. This inevitably leads to the question of why we need three different tuners in our HDTV?

Simply speaking a TV tuner is the electronic device inside your television which converts incoming signals from Over-the-Air television (OTA) broadcasts or from your cable company into audio and video signals which can be displayed on your television.

The original type of television tuner, which has been the standard for converting analog OTA signals since the 1940's, is the NTSC tuner. By September of 2011, virtually every major conventional television station in Canada will have ceased to broadcast analog OTA signals making the NTSC tuner inside your television obsolete. In the United States, analog broadcasts ended in June of 2009.

When the switch from analog to digital television was proposed in the United States in the early 1990's, it was necessary to develop a new type of television tuner which could receive and convert digital television transmissions.

The specifications for digital tuners were finalized in 1995 by the Advanced Television Systems Committee (ATSC) and the tuner was named after the committee. To distinguish the older analog tuner from the newer digital standard, the analog tuner became known as an NTSC tuner. NTSC stands for National Television System Committee. The NTSC was a group , formed in the United States during the 1940's by the Federal Communications Commission (FCC), whose job it was to develop and maintain television broadcasting standards in the United States. To ensure compatibility with its neighbour to the south, Canada has always adopted the standards set out by the NTSC.

Since most HDTV buyers will hold onto their television sets for many years, manufacturers built both ATSC and NTSC tuners into their television sets thereby ensuring consumers could receive OTA analog signals prior to the transition to digital broadcasting and OTA digital signals after the changeover.

The final type of tuner found in today’s digital television is the QAM tuner. QAM stands for "quadrature amplitude modulation" and it’s the standard used by cable companies for sending digital television signals to digital cable subscribers.

In an ideal world, a QAM tuner would replace the need for a cable set top box. Unfortunately, this is not the case because the QAM tuner inside your HDTV can only decode non-encrypted digital cable channels. Since the vast majority of Canadian cable channels are encrypted and require a cable set top box to decode, the QAM tuner is of little value.

Discuss HDTV tuners further in Digital Home's HDTV Forum .