Salem Media Group is working on an interesting project in San Francisco, building a four-tower AM array atop a large commercial building.
While this is not the first AM installation on a rooftop, I find it fascinating to learn about special challenges that such projects present.
This facility will serve two Class B stations: KFAX on 1100 kHz, which will run 50 kW through all four towers by day and night, and KTRB on 860, with 50 kW into one tower by day and 6 kW into all four towers by night.
The stations currently broadcast from other sites under special temporary authority. Their studios are in Fremont.
The new project, underway since 2023, actually marks a return of these stations to their originally licensed transmission site, which they departed temporarily in late 2022.
“Our landlord had sold that land to a developer,” said Senior Vice President of Engineering Scott Foster, “but as part of the deal they retained an easement for us to put the towers on the roof of the building. We also have a two-story space in the building for our transmitters.”
The new structure is a large warehouse-style building of about 200,000 square feet, with truck bays on one side.
Returning a complex AM tower array to the site is a huge undertaking.
Tight coordination was required with Dermody, the industrial real estate company that owns the site, as well as with the general contractor for the building, FCL Builders. On the RF side, Tom Jones and Herman Hurst with Carl T. Jones Corp. have done all the filings for FAA and FCC applications.
“The nice thing is the array is going back the same way it was, just 40 feet in the air,” Foster said.
Salem VP of Engineering Scott Horner is leading the project, assisted by Steve Smit, Salem’s newest project manager, and local engineer Craig Roberts.
Magnum Tower will provide four towers, each with a 12-inch face, standing 186 feet. The project is in the flight path for Hayward Executive Airport, so Salem is limited on the height. Tom Jones designed the system for the shorter towers.
“We will deploy four elevated guy anchor locations, and the balance will be anchored into the building parapet wall. We also will be installing an LED light system.”
Foster told me there have been several engineering challenges. The first was the ground system.
“We were limited by the building owner on the look of the exterior of the building, and they didn’t want to give up any square footage on the inside,” he said.
“Also, the construction was a tilt-up style of building, where sections are built on the ground and then lifted up by crane into place. We were able to install ground cables in the walls before the concrete was poured. Pigtails were left on either end of the wall so that we could connect a 4-inch strap to them later to extend the radials out in the ground to the edge of the property.”
He said the towers themselves create a unique load on a building. All loads had to be calculated and passed to the building design team; they would revise their standard drawings to accommodate the additional load of the towers and guy wire system.
“Finally, there is the grounding design on the roof. The normal radial system would not provide ample protection from equipment interference, according to the models,” he said.
“We will be laying out normal screen for 20 feet around each tower, then increasing that to 18-inch squares for the next 20 feet around each tower. Finally, the rest of the roof will be covered in 3-foot squares of normal radial wires that will then be tied into the strap around the edge of the roof.”
At the base of each tower is an elevated platform that will contain the ATU cabinet for each station, the filter cabinet to reject the other station from the RF chain, and the combining cabinet to get the two signals on a single run of copper to the tower. In the transmitter rooms, each room will have transmitters and phasor cabinets.
As of late July, work on the ground system and elevated guy anchor points was underway.
“We are expecting to start stacking steel by the end of August. At that point it will be all hands on deck as we work on multiple trades. We are hopeful to be completed by the end of 2025.”
Radio World plans a feature on this interesting project when it is completed.
