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Under a Cocoon, ESB Plans for New FM Era

Soon crews will begin to assemble a three-bay auxiliary master FM antenna inside the enclosure


Radio World loves hearing about your RF and audio facility projects. And they need not be atop an iconic skyscraper, as in Scott’s story on this page. Write to me with your own at [email protected].

— Paul McLane

More than 1,250 feet above midtown Manhattan, a big part of New York City’s future FM infrastructure is taking shape inside a protective cocoon of structural fabric that surrounds the base of the Empire State Building’s historic broadcast tower.

“This is the largest construction enclosure ever mounted atop a functioning skyscraper,” says Shane O’Donoghue, director of broadcasting at Empire State Building of the enclosure, which wraps around the lowest 35 feet of the antenna mast where it meets the original top of the 1931 landmark. “It has met all New York City Department of Buildings requirements and landmarks approval, and it’s structurally supported on the tower itself.” The new structure is visible even from street level 104 stories below.

Photos courtesy Skanska

What’s being born inside the cocoon?

The first stage of construction this winter is reinforcing the mast, now more than six decades old, to prepare it for potential future antenna moves at the Empire State Building. With the digital TV repack coming, the current lineup of TV antennas on the tower may change, though exact details are still up in the air awaiting the results of the FCC’s spectrum auction and the business battle for tenants between Empire and the Durst Organization’s new One World Trade Center site.

Whatever happens in the TV world, there’s potentially a complex chess game ahead on the building’s mast. Antennas may require reworking or have to be moved on and off the tower, all while causing as little disruption as possible to other broadcast tenants and to the public observatories that sit just below.

That’s a big reason for the cocoon’s next stage: Sometime in early 2017, crews will begin to assemble a three-bay auxiliary master FM antenna inside the enclosure. Designed to serve all 19 of the FM stations that now call the building home, the new auxiliary antenna will closely replicate the coverage from the two-bay master antenna and one-bay “mini-master” that sit more than 100 feet above it on the tower.

“The antenna has been designed and is in the procurement phase, along with the 19-station combiner,” says O’Donoghue. The new combiner will provide a much-needed backup for the existing ERI combiner on Empire’s 85th floor, which feeds the 1990s-vintage ERI master antenna that serves 16 FM signals.

At present, those 16 stations, as well as the three that use the “mini-master” installed after 9/11, can’t be used when climbers are on the tower. The present Alford auxiliary master antenna that rings the 102nd floor observatory and which celebrated its 50th anniversary last year is no longer adequate.

The cocoon itself is helping to reduce the need for antenna shutdowns on the tower above. The fabric that wraps the new structure, made by the Swedish manufacturer Haki, serves as a construction enclosure, allowing workers to operate inside the enclosure during the day without any RF shutdowns of the primary antennas.

For creating a unique work environment, O’Donoghue credits Skanska, the building’s contractor JLL, the building’s project managers and engineering teams from Plan B Engineering, and Thornton Tomasetti, the building’s structural engineers. The cocoon, accessed through the hatch on the 104th floor at the very tip of the building, contains several levels of work platforms, all surrounded by an enclosure that protects not only against RF but weather as well. It’s nearly waterproof, designed to survive 100-mph winds, and it’s even adorned with LED lighting as part of Empire’s trademark nighttime display.

Because the cocoon hangs off the tower, it also provides a new viewpoint that few people have ever had the privilege to see.

“You stand on the bottom platform,” O’Donoghue says, “and you’re looking down on the 1,250-foot top of the original building.”

Once the new auxiliary master is in place and the cocoon comes off next year, O’Donoghue says the next stages of TV antenna construction on the tower will become easier.

“The uniqueness of this construction,” he says, “is that we’ve designed a climbing aperture inside the tower that allows workers and material to be transported through the active 19-station auxiliary FM antenna to an ice shield above it that will act as an RF shield, allowing work to be performed on antennas above while the 19 FM stations remain on the air from this new auxiliary antenna.”

That means that the FM tenants will be able to make seamless switches from the upper master and mini-master antennas to the lower auxiliary master without causing disruptions to their signals.

So far, O’Donoghue says, Empire has signed a 16-year lease extension with one FM broadcaster, Emmis Communications, to use the auxiliary master; it’s working on negotiating deals with other tenants, though Empire declined to identify them. Major broadcasters with operations in the city include CBS Radio, Cumulus, iHeartMedia and other familiar names.

O’Donoghue says the current ERI master antenna still has many years of life left in it. Less certain is the fate of the 1965-vintage Alford antenna, which likely won’t be needed once the new auxiliary master is in place. “No decision has been made yet,” he says about that piece of broadcasting history.

In the meantime, he’s excited to be helping to write the next chapter of FM there.

“The history of radio at Empire is an incredible history,” O’Donoghue says, “and to have had some impact here has been really great.”