Maybe this has been answered before, but what are the HAM radios found throughout the world for? You can activate them, but all you get is static. Please, no spoilers if possible.
The radio towers broadcast the signal from a nearby ham radio. You can use the sound to find a hidden area when you activate the radio tower. Walk in the direction where the signal gets stronger. If you find the signal getting weaker (the morse code gets quieter and there's more static noise) as you move away from the the tower, you're going in the wrong direction. For example, I just found the Papa November one - I went a short distance from the tower to where the signal was stronger, and found a sewer entrance to a drainage chamber. Inside I found a skeleton, some supplies, some components for making weapons from schematics, and a ham radio transmitting the Papa November signal - when I turned off the radio the signal was removed from my station list.