in that case, forget the roleplay part, just make it so that you can find a bunch of (immobile) radio stations across the map which you can use to communicate with people at the other stations
since the server has local chat I could see this being useful
You're still missing the point. That is roleplay no matter what you do. Why would you use morse code to communicate to the other side of the map? That would make no sense. You've got a rifle, a pistol, some ammo and some rations, nothing else. Now you're going to hold up in one spot for a huge span of time, focus entirely on a button, hope someone is on the receiving end, and then communicate.
the other big point is, why would two people communicate like that? It's not reliable. If it was like two forts, and we were talking about 2 groups of 10 communicating: yes, yes those NEED a way to communicate. But this is survival. You won't GET two groups of 10. You'll get a group of 3 and a group of 5 at most, and then a bandit surprises one group and boom, everything is lost