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On the Air

Bringing broadcast back after the loss of 1 World Trade Center

4 min read

Samuel K. Moore is IEEE Spectrum’s semiconductor editor.

26 October 2001–Many New Yorkers were alerted to the 11 September attack on Manhattan not by an announcement, but by silence. The 110-meter mast atop 1 World Trade Center was a broadcast hub for all of the New York City area, supporting FM radio as well as nine TV stations, including local affiliates of CBS, NBC, and ABC. When the first airplane hit, transmission was lost. New Yorkers began surfing their radio and television channels to find out the cause, and broadcast engineers began to see new value in backup transmission sites.

"[One World Trade Center] was the big stick in that part of town," said James Fryer, president of Towersource.net, which keeps tabs on the industry and maps out the locations of the country’s transmission towers. "It will not be quickly or easily replaced."

Most broadcasters scrambled to get back on the air by bringing low-power transmitters and antennas to alternative locations within days of the attack. But those temporary stations left many in the New York area, especially the roughly one fifth of households with no access to cable or satellite services, with poor reception. Bringing coverage back to normal will be a long and difficult process. In fact, TV broadcasters cannot say exactly when it will be complete.

Given the costs and regulatory complexities of finding another full-power transmission site, a joint project is the only possibility. "There’s no way each station can go it alone," said Bill Beam, director of engineering at WABC. So TV stations, even those not displaced by the attack, have formed a working group to find a joint solution. "The broadcasters have agreed to look at all the options and are open to anything that will work," said Ken Devine, vice president and chief technology officer at WNET, which is spearheading the effort.

Finding a new site is incredibly difficult said Gary Cavell of Cavell, Mertz & Davis Inc., in Fairfax, Va., one of many consulting engineering firms working with New York City broadcasters. "There’re not a lot of available sites in New York." A further complication is created by the regulatory requirements of the U.S. Federal Aviation Administration and the U.S. Federal Communications Commission.

The FAA’s concerns include the impact on flight paths of a new antenna mast, as well as the risk that the RF energy from new transmitters will overload or interfere in aircraft communications systems. The FCC is concerned with protecting nearby TV and radio stations from interference, ensuring coverage of the community in which a station is licensed, and maintaining an equitable distribution of services. This last worry means ensuring that if a region is not as fully covered by the new transmission facility as it once was, it has access to a certain minimum number of stations from another source.

"The farther we get from the World Trade Center, the more difficult this becomes," said Devine. That is in part due to the proximity of stations in neighboring regions. Moving transmission away from its traditional location could lead in one direction to interference with transmitters in neighboring markets and in another to loss of coverage. "TV stations are packed so tightly in the Northeast corridor that it’s like a bunch of dominoes. If you shove one the wrong way, everything falls apart," said Cavell, who is also president of the IEEE Broadcast Technology Society.

In the aftermath of the attack, WCBS wound up being the only major broadcaster able to reach those without cable or satellite access to it in the New York area. According to its vice president of engineering and advanced technology, Robert Seidel, WCBS activated its back-up transmitter, a 35-year-old piece of equipment, by remote control soon after the attack. Even though the station was far less affected by the loss of the World Trade Center setup, it is still responding to the attack. It is installing a new 30-kW transmitter at the Empire State Building originally intended for the World Trade Center. The station is also adhering to its history of maintaining geographically diverse backups. Seidel said the company is building a backup antenna atop its corporate headquarters in midtown Manhattan.

Meanwhile, two stations have relocated to the Empire State Building, and five have headed across the Hudson River to the 120-meter Alpine Tower in New Jersey, constructed in 1937 and home to the first FM station. Both sites may have some problems accommodating the new residents. Several of the stations that began broadcasting from Alpine to the New York area with low-power transmitters have acquired or installed more powerful equipment, so that Alpine will need to bring in more power.

The Empire State Building is crowded with other transmitters and antennas. Stations like WWOR and WNYW have had to install their temporary antennas below the building’s antenna mast. The building also shares the World Trade Center’s fame as a U.S. landmark, and has been evacuated in response to a bomb threat since 11 September on at least one occasion. Even so, it is under consideration as permanent home by the broadcasters’ working group, according to Devine.

In the past, stations built safeguards into their systems by having backup transmitters and other equipment at a single site. But "no matter what solution we come to in the end, the hard realization is that we have to be geographically diverse," said Beam.

Several stations were already pitching digital signals. "The loss of those is regrettable, but it will have to take a back seat to restoring analog," said Ed Williams, who leads an engineering division devoted to DTV at PBS, the U.S. public broadcaster. Only CBS had its digital transmitter at the Empire State Building. Digital broadcasting in New York City requires 200—1000 kW, more power than the 50—100 kW for analog VHF, he noted.

While TV broadcasters put together their strategy, many customers with poor reception are turning to satellite and cable. Homes with either or both already dominate the New York City broadcast area, a so-called designated market area encompassing 29 counties, including some in New Jersey, Pennsylvania, and Connecticut. According to Nielsen Media Research, 78 percent of the area has cable, 6 percent has some type of satellite service. Accounting for the overlap, only 17 percent of the designated market area are broadcast-only households. Since the disaster "we’ve seen a spike in demand in New York City," said a Time Warner Cable spokesperson. Time Warner has seen about 15 000 more cable hookups than normal since the disaster. "It’s not the way we want to get customers."

Al Resnick, a consultant to area broadcasters and formerly an engineer with ABC, also helped engineers recover from the Loma Prieta earthquake outside San Francisco in 1989. The biggest difference between the two, he said, was zero fatalities among personnel operating the facilities in San Francisco. Six engineers were reported missing following the 11 September attack in Manhattan.

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