1000 XP, Cash
Talk to Dominic upstairs at the Lifeguard Station to start the quest. Follow the mini-map to the lighthouse. When you get to the lighthouse, it will trigger the Knockin on Heaven's Door side quest. You'll have to go inside and talk to James before you can continue to progress on this quest.
After you talk to James you must do the A Ray of Hope side quest. Once you complete that, you'll be able to get the signal amplifier and bring it back to Dominic.