Martin Moves to Boost DTV Coverage

Concerned about the loss of coverage that some stations may experience as they shift from analog to digital broadcasting, FCC Chairman Kevin Martin said he wants to adopt rules for distributed transmission systems (DTS) that would allow broadcasters to improve or extend digital coverage with multiple low-power transmitters all operating on the same channel as the main station.

Speaking at a press conference in Washington yesterday, Martin said he has placed the DTS rules on the FCC's Nov. 4 open meeting agenda.

"The idea ... is that [DTS] would provide for some additional flexibility for broadcasters to make sure that they are able to cover the same basic contour of service," Martin told reporters.

He said that the proposed rules do not place limits on the number of ancillary transmitters and towers that a station may build.

Rather, he said, they impose limits on the power of the transmitters and leave it to the broadcasters to locate them in a way that duplicates their analog coverage.

The FCC launched the DTS rulemaking in 2005 and it has been ripe for action by the commissioners for the past two years.

Martin said he was prompted to push DTS after the DTV test in Wilmington, N.C., where at least one station, WECT, left many of its old analog viewers behind as it made the shift to digital and a new tower.

In House testimony last month, Martin said that 15 percent of TV stations may reach significantly fewer homes after they begin relying solely on their digital signals next February.

Martin also promised the lawmakers he would look for ways to insure that digital coverage duplicates analog coverage. DTS is apparently one of those ways.

Merrill Weiss, a technical consultant based in Metuchen, N.J., first conceived of single-frequency distributed transmission in 1991 and has been a strong proponent ever since. He holds a key DTS patent and has been involved in various experimental applications of the technology.

He said he was delighted that the FCC was finally acting on rules to make it all possible. "DTS will allow stations to provide service is ways that could never do from a single transmitter."

The technology gives broadcasters considerable flexibility, he said. "You could combine additional transmitters with a big transmitter and do gap fillers to provide service where you can't now because of terrain obstructions or high-rise buildings," Weiss said.

"Or, you could use it to extend coverage. A low-power operator could build some number of additional transmitters at low power and get the equivalent service of a higher power single transmitter, likely with better coverage.

"By putting the transmitters closer to the receiver, you get more reliable signal delivery."

The key to DTS is operating multiple transmitters in the same area on the same channel, Weiss said.

In digital, that's possible because the transmitters are closely synchronized and because of the adaptive equalizers built into every new DTV set and converter box.

The adaptive equalizer is meant to deal with the signal echoes that naturally occur and produce ghosts in analog TV. But in a DTS setup, it performs double duty, sorting out the multiple signals on a single channel.

Weiss said that there have been two full-blown applications of DTS in Reading, Pa., and State College, Pa., and that broadcasters have been experimenting with it in New York and another large market he declined to identify on the record.

DTS is particularly well suited for mobile broadcasting applications, where it's difficult to deliver a steady signal to a moving receiver in ever-changing environments.

With a good DTS array, Weiss said, broadcasters can achieve "signal reliability roughly equivalent to what you can get with a cell phone."

For more on DTS and how it works, go to TVNewsCheck's interview with Weiss in September 2007.