I'm having trouble expanding my base past 14 people. In the help section of the game it mentions that you can build a radio tower to help recruit new people. In the forums I have seen several people referencing building it. The issue I am having is finding the radio tower to build. I don't see it anywhere in the build options. There is a option for a studio at 20 people. Where do I find the tower?

The Radio Studio is the tower. In the actual Fallout game it's a tower so people are probably referencing it like that because it's what they are used to saying. If you upgrade your studio it might have another name. I have one but I have yet to upgrade it so I don't know what names it changes to when you upgrade it.