Distress signal (Relay tower 1DL-109)

Distress Signal is a quest in Fallout 4.

Other distress signals

 * There are three of these signals in the quest The Lost Patrol, each one leads to a dead Brotherhood of Steel member.
 * There is a distress signal station found by activating Relay Tower 0DB-521 in the Glowing Sea. It leads to a cave which holds the body of a raider, and his suit of power armor.

Quick walkthrough
Found when extending the Relay Tower 1DL-109. A woman says she is hiding in a train car with "Thomas." Shortly into recording she describes her hiding spot as a train car.

Detailed walkthrough
Go SE from the radio beacon until you meet the train tracks and find a train with several feral ghouls. The fourth car along (blue car, turned on its side) has a hatch to enter the train, hidden behind a bush. If you're having difficulty finding it, it's the only bush touching the train on either side. Inside next to a ham radio are the skeletal remains of the woman in recording, along with a locked crate.

Bugs
This signal and the nearby Boston City Works Beacon and Garbled Radio Beacon do not turn off when their original ham radios are turned off by the player.