Digital TV in the U.S.

What's on and how?

TV stations in the nation's 10 largest markets were slated to begin digital TV broadcasts by 1 November 1998, but beat their own self-imposed deadline by three days. About two dozen stations carried Senator John Glenn's launch aboard the space shuttle on Discovery live in high definition. It was an auspicious start to digital broadcasting, but what stations do for an encore is more prosaic—and for the time being, minimal.

The major networks' use of DTV over the short term is mostly limited to prime-time evening viewing hours and the occasional special event. At prime time, for example, CBS will run movies, which are both a readily available source of HDTV fodder and inherently high-definition, like other programming shot on film. The rest of the day, the network-owned and -operated stations will upconvert their regular National TV Systems Committee format programming to a high-definition-like 960 interlaced lines—with Snell &Willcox equipment—for broadcast on the DTV channel.

As for live events, CBS last winter carried a handful of National Football League games in HDTV, but has not announced further plans. Nor has NBC. At this writing, the network had not broadcast any digital TV, although it says it will produce The Tonight Show in HDTV this fall. Fox Network is similarly mum on any DTV plans, except to say it is unlikely to do sports in HDTV owing to a lack of production equipment. ABC's digital TV menu is similar to that of CBS: movies in prime time and an occasional special.

PBS will air monthly night-time specials in HDTV, although perhaps more interestingly, the public network recently said it will begin a 24-hour PBS Kids Channel this summer as a standard-definition multicast. The network also says it will aggressively pursue interactive features for its digital TV programming with chip-maker Intel Corp. First up is the kids' show Zooboomafoo .

As for cable, at press time, the issue as to whether cable operators "must carry" digital TV broadcasts-and in what resolution-had yet to be settled. If and when it is, there will still be a question of how the quadrature-amplitude modulation (QAM) used by some systems will pass through DTV's 8-VSB signal. (Remodulators on the cable set-top box or the DTV are a proposed solution, as is an HD-l080 component video connection,) Meanwhile, Time Warner Communications Inc., based in Englewood, Colo., has agreed to carry CBS's digital broadcasts intact on its upgraded systems. Cablevision Systems Corp., Woodbury, N.Y., also will transmit ATSC-format HDTV to carry the major league baseball, basketball, football, and hockey teams for which it has the local franchise.

With cable interoperability gaining ground, digital satellite carriers cannot afford to let the grass grow under their feet. Beginning 6 March, DirecTV of EI Segundo, Calif., was to begin transmitting movies and other fare from Home Box Office on a high-definition channel, and will likely offer another for pay-per-view movies. It has already signed up New Line Cinema, Los Angeles, as a content provider. EchoStar Communications Corp., too, has plans to send HDTV by satellite, though no schedule has been announced by the Littleton, Colo. company.

Elsewhere, Unity Motion, St. Louis, Mo" will offer movies, sports, and other programming by subscription over three satellite channels, These will be received by its set-top box, which also includes terrestrial DTV tuning and decoding. Unity and EchoStar will use true ATSC formats whereas DirecTV's HD channel has 1080 interlaced lines but 1280 pixels per line rather than 1920.

To turn to the formats the networks will use, CBS and NBC are committed to 1080 interlaced lines at least for prime time. ABC will do HDTV, too, but in the 720-line progressive format, and Fox is to be all-progressive as well, but has not yet revealed if that will include any HDTV. Both Fox and ABC contend that going noninterlace positions them well for a future that holds progressive scan displays of the plasma and LCD type, as well as more CRT-based displays capable of non¬interlace scanning. — S.A.B.