We just completed the design of a technically complex, stacked VHF antenna array that San Francisco broadcasters KGO-DT and KRON-DT will install later this year atop Sutro Tower, in the City’s busy downtown area. As part of the repack, KGO, the market’s ABC O&O station, is moving from VHF channel 7 to 12. Once channel 7 is vacated, KRON will move there from UHF channel 38 (virtual channel 4).

“This is one of our most complex repack antenna designs, due in large part to the strict earthquake code that applies to antennas that are installed in the Bay Area,” said our VP/GM Keith Pelletier. The final designs are being reviewed by a third-party structural engineering firm, in San Francisco, to ensure that this array is in full compliance of the City’s earthquake code.

The stations’ chose to customize Dielectric THV Series directional pylon antennas with low-windload, top-mount (slotted coaxial) designs to avoid possible interference between the antennas and the tower that could affect radiated patterns and power levels. After the antennas ship in June, a tall-tower crew will install them by the end of the year—well ahead of the repack deadline—on one of the three “candelabra” arms extending from the top of 977-foot tall Sutro Tower.

The stacked array will also be reinforced with guy wires, anchored at the top of the candelabra platform, specifically to meet the earthquake code. And, KRON’s antenna will be made of stronger, thicker steel to ensure it can support the weight of KGO’s antenna in the stacked array.

“We will also provide a Dielectric TLSV series VHF auxiliary antenna that will be installed lower down on the tower that will allow KGO to continue operating on channel 7 with no down-time,” Pelletier said. Once the installations are completed, KGO will move to its permanent antenna at the top of the tower, and the aux antenna will remain on the tower.

Of the 900 TV stations that Dielectric is assisting with repack, 50 have selected a stacked antenna array design, which is a “Dielectric-developed specialty.”