WGBH Chooses ERI’s SHPX-8AC

Lambda mounting system presents a uniform mounting structure to each bay
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BOSTON — It’s strange how some listeners can better receive other stations but not the one you’re working for. And when you decide to work at a different station? There’s no escape there, all the others will continue to sound fine except yours. It’s a law or something.

WGBH(FM) at 89.7 MHz on your cute radio dial with the scratchy tuning capacitor is Boston’s highest power radio station at 98 kW — but power level does not guarantee reception. When WGBH changed programming, audience feedback indicated we needed a different signal delivery system to better serve evolving receivers in cars, homes and personal devices.

Our transmission facility is southwest of Boston in Milton, Mass., atop Great Blue Hill — that’s where the “GBH” comes from. Since the late 1970s, our antenna was an eight-bay, full-wave-spaced SHP-8AC manufactured by Electronics Research Inc. When shiny and new, the SHP delivered programming to stations of the Eastern Public Radio Network. Farthest out was Albany, N. Y.

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Workers are preparing the 100-foot lambda section for WGBH’s new antenna mounting structure. POLE CONSIDERATIONS

The eight-bay was chained to a 100-foot tapered pole mounted on a 130-foot Dresser self-supporting tower built for WGBH(TV) 2 in 1954. The pole diameter was more than 20 inches at the bottom and shrank to 6 inches at the top. Complex pattern distortions would result from pole and antenna flexing in moderate winds, especially the upper part of the taper.

The WGBH Radio engineering team — Emeric Feldmar, Thomas Devlin and I — considered ideas for a replacement antenna. Based on performance and endurance, we thought the SHP should be replaced with another ERI antenna. A panel antenna was considered, but most are quite heavy and would require additional transmitter power.

ERI Eastern Sales Manager Carl Davis evaluated our situation and suggested replacement of the tapered pole with a 100-foot lambda section manufactured by ERI’s tower division. Carl explained that the lambda mounting system was designed to present a uniform mounting structure to each bay of the antenna, allowing the energy from the bays to combine much as they would if the antenna were in free space. This was a much better alternative to modeling the tapered pole, with the added benefit of minimizing the flexing previously observed. We decided to continue with a similar antenna, ERI’s SHPX-8AC.

In the summer of 2014, ERI conducted a series of detailed tower structure studies for the new lambda and other custom fabrications. The ERI tower crew arrived in August: Mike Boyer (foreman), Jeff Salazar, Tung Phan and Colin Harrington. Peggy Hunt managed our project from ERI headquarters.

The crew first installed a temporary antenna on our transmitter building tower, then removed the old SHP antenna. A crane lowered torch-cut tapered pole chunks to the ground. In concert with the tower construction, Dan Dowdle and Tom Scharf at the ERI test range were preparing a series of 14 pattern choices. Our pattern selection was translated into tower crew directions for installing the lambda system and our new SHPX antenna.

The new antenna was final tuned on Sept. 13 and placed on-air at full power. The ERI crew was on-site for about 15 days and it was a great pleasure working with them and all the folks at ERI. The system has performed flawlessly.

Best of all — the listeners who could only get the other stations? Well, we haven’t heard from them yet.

For information, contact Joe Meleski at ERI in Indiana at (812) 925-6000 or visit www.eriinc.com.

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