I haven't done much with these, but I followed one and I kept getting a signal strength indicator that helped me zero in on the source. But Now I've tried to find and follow more and I see that many of them don't have a signal strength indicator. How the heck am I supposed to zero in on these? For example, I think I've followed the Greenbriar signal to the point where I get no static, but I can't find this bunker by the river that the recording mentions. I know I can just look it up on the wiki, but I want to understand how I'm supposed to find these w/o cheating.