The tower has an open terminal which you can use to amplify the signals in the area. Doing so will allow your Pip-Boy to receive three new signals:
You might encounter a power-armored NPC named Duke north of the relay tower. Talk to him and he’ll put the Atom Cats Garage’s location in your map.
Signal Sources
The Distress Signal is found in the underground shelter in Fiddler's Green Trailer Estates. Check the location's page to locate the shelter's entrance.
The Civil Alert System Broadcast is being broadcasted from a ham radio inside the military bunker at the base of the satellite dish of the Fort Hagen Satellite Array. Check the location's page to locate the bunker's entrance.
The Raider Radio Signal emanates from another underground bunker NW of the relay tower. Just follow that general direction and you'll find a metal fabrication with the bunker entrance beside it. The bunker is really small so you'll only find the ham radio and Novice locked chem cooler inside.