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New Master Antenna System Serves D.C.

Combined FM installation features a four-bay, three-around ERI panel

The new antenna systems atop the AU Tower serve six FM stations in the nation’s capital.
Photos by Peggy Miles except as noted.

Washington, D.C., has a new master FM antenna system looking down on the city from high ground around The American University campus. In addition to a big new panel, the job added new antennas for two other stations. Radio World talked with Rob Bertrand, WAMU’s senior director of technology, about the recently completed project.

Radio World: Where did this take place?
Rob Bertrand: The project took place on the 419-foot broadcast tower on the campus of American University in Washington, D.C. I’ll call this the “AU Tower.”

RW: Make and model of the antenna systems?
Bertrand: The new panel antenna is a four-bay, three-around ERI Cogwheel antenna that serves WAMU, WTOP, WPFW and WETA. There is a new ERI SHPX Rototiller in place for WPGC and a new ERI LPX Rototiller for WMMJ. The combiner is all new; it was designed, built and installed by ERI.

RW: Describe the scope of the job.
Bertrand: The AU Tower has been the home to multiple FM stations since the 1960s. Additional stations were added in the 1970s and ’80s, with a final station in the early ’90s.

It is the primary broadcast home to WAMU, The American University’s NPR station; Hubbard’s WTOP; Urban One’s WMMJ; and Pacifica’s WPFW.

WAMU and WETA also provide reciprocal aux sites for one another, so WETA has an aux presence on the tower. They had been sharing the WAMU backup antenna but will now be part of the combined antenna.

WAMU Senior Director of Technology Rob Bertrand, center, stands with station Director of Engineering Andy Gunn and ERI President/CEO Tom Silliman.

WAMU joined the WETA combined antenna in 2019 in preparation for this project. Finally, WPGC (Entercom) has maintained an aux presence on this tower since the early 1990s.

What is interesting about this group of stations is that WTOP and WPGC are both directional, which meant that not everyone could join the master system. However, ERI devised a method for WTOP to meet its required directional pattern into the left-hand circularly polarized input to the new antenna system, with the master combiner feeding the right-hand CP input.

WPGC is highly directional, as it’s licensed to Prince George’s County in Maryland. Its antenna was upgraded, but it remains separate from the directional system on a mast up above the new antenna.
WMMJ, a Class A station, has had such incredible ratings success from its standalone antenna. In fact, WTOP, WAMU and WMMJ often switch places in the ratings for the #1, #2 and #3 spots in the market. Because they’ve done so well, Urban One leadership was hesitant to join the new antenna system, though they opted to replace their 30-year-old antenna as part of this process.

The new panel system is maneuvered through campus.

RW: Why was the new system necessary?
Bertrand: When the current array of antennas on the tower-top pole were erected in the early 1990s, these were fundamentally different stations in terms of community impact. WAMU was a tiny bluegrass station, routinely ranking toward the bottom of the ratings in the market. The station that is WTOP(FM) today was WGMS, a classical station that held its own often around the #15 mark, but was hardly the powerhouse WTOP is today. WTOP and WAMU currently lead the market, locally and nationally, within commercial all-news and public radio, respectively. They are massive stations.

In the legacy build, rather than opt for a costly master antenna, WAMU was built as a six-bay on the tower-top pole. WGMS was a three-bay directional, interleaved with the top three bays of WAMU on one side of the pole. WMMJ’s two bays straddled WAMU’s bottom bay. WPGC towered above all of them with its own directional antenna.

Assembling the SHPX antenna for WPGC, to be mounted above the panel.

It was a mess. It made sense in the early 1990s given the economic realities for all these stations, but as they evolved into market leaders, they were sorely in need of “getting out of each other’s way” and an upgrade to an antenna system that would maximize audience for each station.

On top of that, these antennas were built on a “stepped” pole with the largest diameter at 16 inches OD and the narrowest at 6 inches. It was just a difficult situation.

Multiple driving measurement tests were performed over the years. We did one in 2017 with WTOP over the span of 900 miles of driving loops around the DC region. The test made clear what we had suspected: Each station was underperforming to the “opposite” side of the tower top pole — which was also the location of the adjacent antennas.

ERI field technicians assemble part of the four-station FM channel combiner. It feeds the master FM antenna, which includes dual inputs; one is nondirectional for WAMU, WETA, WPFW and to provide auxiliary facilities for WTOP(FM), the other input is directional and will be WTOP’s licensed main antenna. The site also includes new antennas for WMMJ and WPGC. Photo by Rob Bertrand

When I moved to the market in 2016 to join WAMU as its technology head, I was so surprised that at my apartment at the time, which was next door to the studios, I had a hard time receiving the station. This is two miles from the tower at that spot, and the ability to receive the station varied widely from one day to the next. Far away from our six-bay antenna, the station performed well to the north; but close-in and to the south we did not do well.

Finally, American University decided that it was time to decide once and for all what to do with this unique non-core asset sitting on its campus. Should they keep it or sell it? And if they kept it, who should run it? We pitched the idea of running it and performing this upgrade, with the goal of achieving full ROI in less than 10 years.

RW: How was the work managed?
Bertrand: WAMU led the project and managed it from concept to final construction. WTOP was a key partner and they were also an equal shareholder in financing the costs directly related to the antenna and its installation. It was unique that these two giant competitors worked so well together on this project, but from top management to the engineering teams, we all knew it was in our mutual interest to build the best facility we could, together.

The tower before the new pole was installed.

WAMU has ultimate ownership of the antenna, but WTOP is a major “shareholder” in the system because of their investment. The other antennas are owned by their respective stations and parent companies.

RW: What was the project budget?
Bertrand: The project in total cost $2.8 million, excluding the rototiller antennas and their transmission lines. The project included a new shelter from VFP beneath the tower to house the combiner system as well as massive reinforcement and reconstruction of the tower from top to bottom. It also included replacement of that stepped pole with a uniform-diameter pole with massively thick walls for stability. There were also additional costs local to individual stations related to these changes. All in it probably clocks in just north of $3 million if you tally everyone’s respective investments.

RW: What are the other critical components?
Bertrand: The system has a four-station combiner for WAMU, WPFW, WETA and a unique low-power nondirectional aux for WTOP.

The tower with the new pole and antenna systems.

WTOP has the ability to broadcast at full power from its directional input to the system or at lower power via the combiner as a backup, in case anything happens to its directional infrastructure.

The system also includes the requisite bandpass filters for the noncombined stations as well as a versatile patch panel system for lockout/tagout and emergency operation.

RW: What other key players were involved?
Bertrand: Vertical Technology Services of Hagerstown, Md., performed the tower structural modifications and removed the old tower-top mast and installed the new mast. They also installed the custom cogwheel antenna and support structure, as well as the two additional single-station rototiller antennas.

A dizzying look down from 400+ feet.

The structural engineer of record was Richard Dyer of Morris Ritchie Associates. James Ruedlinger, who heads the structural division for ERI, designed the tower modifications and the complex rigging plan. Bob Clinton of Cavell, Mertz & Associates was the FCC consulting engineer and contributed to our antenna design process, as well as handling the FCC applications for most of the stations.

The general contractor for ground support was Network Building & Construction services, who primarily supports cellular buildouts and was adept as a permit expediter with the District of Columbia as well as supporting building the temporary roadway and ground support needed for the tower crew. Our new combiner shelter was designed and built by VFP shelters of Salem, Va. Paul Shulins and Dave Wing of Shulins Solutions did the installation of the Burk Arcturus system, which was engineered by Mark Raymond and Chuck Alexander of Burk Technology.

RW: What other technical aspects of the project will Radio World readers be interested to know about?
Bertrand: We have installed the Burk Arcturus system to provide VSWR protection and full monitoring of the system, such as line pressures and temperatures. We were drawn to Arcturus because of our familiarity with the Burk ARC Plus platform and its hardware, as well as the promise of predictive analytics.

Crew foreman Craig Fowler of Vertical Technology Solutions poses with the remains of the old tower pole that has just been extracted from the top of the tower.

We’re monitoring everything from VSWR at all the inputs and outputs of the system, line pressures, every dehydrator parameter including run-time of the redundant pair, line temperatures, to external temperatures and security parameters.

The goal is to be able to develop a complete picture of normal system operation across all seasons and be able to trend anomalies over time before they become major problems. The Arcturus also manages interlocks for the full facility and will automatically disable transmission based on which transmitters are switched to which antennas, depending on where a VSWR condition is detected.

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