Finally, let's get that repeater unit set up in the local radio tower.
Clean up Damonta
Arriving in Damonta you'll soon realise the place is overrun with robots. Follow the path left. Veering right leads to a small building with a vendor. Kill the robots here and follow the curve. Red Baychowski will call you from inside the plane and offer you a side quest that can be completed in the airplace graveyard just north of Damonta.
Continue around the curve to meet Werewolf Wally who will ask you to save Damonta. If you have a high enough Hard Ass skill you can bypass this quest-line completely.
If you want to save Damonta head south and around the buildings housing the radio station. Follow the path into the area full of airplane junk. There's a lot of robots here as you're getting close to the robots HQ, but keep going until you reach the far left wall. Go north from here and follow the path right to a hangar with a synth called Tinker inside.
Fight the enemies here and try and save the girl in the chair from dying. Once the mission is over you can go back to the radio tower and turn it in to Wally to gain access to the control panel to install the Repeater Unit. Once this is installed you'll be asked to go back to the Ranger Citadel and then on to investigate the mysterious signal out of California.
Side Quest: Find Binh
You get this quest from the family in the diner around the rear area of Damonta. Binh was last seen in the garden, they say. Go up the road from the diner, kill the robots surrounding the garden and look for Binh. She's not there because she's the girl you saw earlier in the hangar with the synth Tinker. Whether you saved her or not, talk to the parents afterwards to complete the quest.
Side Quest: Help Red find the Treasure of the Sierra Madre
Go out of Damonta and up to Silo-7. Take the left path until you come to a corner with two wrecked planes. Use Perception to find the entrance and inside you'll find the Sierra Madre. Go inside the cargo hold and use Brute Force or Lockpicking to open the grate and split the treasure with Red.