In order to follow Hank Madigan's trail, the dwellers need to reach the top of the Top of the World. Problem is, a raider named Rose is unwilling to let them access the uplink chamber, unless they repair the radio station for "her."
With it in hand, the player has to head to the National Isolated Radio Array and mount it in the auxiliary dish to the northeast. Problem is, doing so spawns a horde of robots by the chainlink fence to the west, just beyond which lies the hut where the player has to redirect the power, on the terminal.
After wiping the robots out, the player simply has to reroute the power and return to Rose at the Top of the World. She will let them up and allow them to "meet" Hank Madigan. Looks like she needs a couple more favors to really open up and allow the player to get what they need.
Find the Signal Repeater Schematic
Read Signal Repeater Notes
Search for an RCX01-A39 Duplexer
Search for an SMU-97 Transponder
Construct the Signal Repeater at any Tinker's Workbench