What is the difference between NTSC, ATSC and QAM?

If you have been shopping for TV Tuner cards for your homebrew DVR or an HDTV lately, you’ve probably run across the following acronyms: NTSC, ATSC and QAM and wondered what they are.

NTSC refers to the committee that created the standard called the National Television System Committee. The National Television System Committee was established in 1940 by the Federal Communication Commission (FCC) to resolve conflicts which arose between companies over the introduction of a nationwide analog television system in the United States. In March 1941, the NTSC approved the technical standard for black and white televisions.

The committee was reconstituted in January 1950 to create a standard for color television. In March 1953 the Nation Television System Committee approved the NTSC color television standard.

The NTSC is the standard television system in the United States and is not compatible with UK or European transmission systems called PAL (Phase Alternate Line).

In 1982, the Advanced Television Systems Committee was created to generate a standard for digital television which is designed to replace NTSC in the United States. ATSC provides for high definition including the 16:9 wide screen format up to 1920x1080 pixels in size. Also ATSC supports “theater quality” sound using the Dolby Digital AC-3 format which provides 5.1 surround sound.

The FCC mandates the broadcasters use ATSC instead of NTSC by early 2009.

QAM stands for “quadrature amplitude modulation” which is the format cable channels are encoded and transmitted via cable. Using a QAM tuner you would be able to receive unencrypted digital signals via your cable provider without needing a digital cable box. QAM tuners are the cable equivalent of the ATSC tuner. Unlike the FCC requirement that ATSC tuners are required in new television sets, QAM tuners are not required.

Integrated QAM tuners allow for reception of unscrambled digital programming sent unencrypted by cable providers, usually local broadcast stations. Since most cable providers consider digital channels as not part of their basic cable packages, most digital channels are scrambled. Which channels are scrambled varies greatly from location to location, and can change over time. In this case you need a digital cable box or CableCARD to unencrypt the signal.

In the United States, any television that is labeled “digital cable ready” can have a CableCARD installed by the cable provider to unscramble the protected channels. This allows subscribers to tune all authorized digital channels without the use of a set-top box. Due to restrictions of the CableCARD, CableCARD slots are not provided on the various homebrew PC tuner cards.

To quickly recap, NTSC is what the current broadcasters use for analog broadcasting for channels like 2-13 and 14-83 while ATSC is used for digital broadcasting. QAM tuners allow you to receive unencrypted digital signals from a cable provider.