ATSC Digital TV – A Tutorial for the DXer

Doug Smith W9WI
June-August 2003
(updated August 2004)

It has become apparent that radio hobbyists' understanding of the ATSC digital television standard used in North America (among other places) is rather minimal. This comes as no surprise – most broadcast engineers, even those responsible for implementing ATSC broadcasts, really don't understand it either! The documents and papers presented so far have been highly technical in nature.

In this series of articles, I hope to explain in layman's terms how ATSC digital TV works, and why the viewer (especially the viewer of distant stations) observes what they observe. Some abbreviations will be defined in the text, others will be expanded in footnotes and explained fully later.

Introduction:

The Advanced Television Systems Committee, or ATSC, was created to develop a system for over-the-air broadcast of high-definition television (HDTV) in the United States. It was largely a reaction to the development of a satellite-delivered analog HDTV system in Japan 1 and the realization that while cable TV systems could implement HDTV at any time, over-the-air broadcasters would need to present a standard to the government for approval.

While the ATSC's task may have been to provide high-definition television, the standard they created allows for far more. A single ATSC transmitter can broadcast:

in a variety of combinations, limited only by the available bandwidth. Some broadcasters are transmitting as many as six standard-definition TV programs on a single transmitter. In the aftermath of the 9/11 attacks in New York City, the ATSC capabilities of WNYE-TV were used to broadcast data for use in the recovery efforts. Some stations hope to provide high-definition TV and broadband Internet access simultaneously over the same transmitter.

The ATSC standard is also multi-layered. Layers may be mixed and matched for different purposes. For example, the MPEG-2 and AC-3 data compression standards are used for hard-disk recording as well as for over-the-air broadcast. The ATSC transport stream standard can be used to broadcast HTML source for web pages rather than digitized video. The whole thing can be used with either 8VSB modulation (over-the-air) or 16VSB. (cable) The commonly-used layer standards:

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