Radio frequency channels should be a thing for walkie-talkies, personal radios and ships to get information to your group, and should be set using something like a 4 digit code, so you can just set your group's radio sets to the same code and be able to communicate across distances depending on how much power goes into your radio broadcaster. There could also be radio jammers (force your code to all zeroes and just have that channel always be static) or able to force it onto whatever channel you wanted within a certain distance so that incoming ships or lone explorers can communicate with your tower before they get gunned down by a corporation/nation.