From the FAQ:
Your first Pod needs to be placed in an area with a strong WiFi connection. A good rule of thumb would be at least one room separating it from your Gateway (within approximately 20 to 30 feet). Then, your remaining Pods should be evenly spaced from each other into outlets throughout your home, close to the areas where you currently have poor coverage.
Putting just one pod in the barn will not work, if you do not already have a strong WiFi connection in the barn.
You'll have to put a pod inside a room of your house, or on that room's exterior wall, as close as possible to a "line-of-sight" path to your barn, and then another pod on the outside of your barn, in that "line-of-sight", to make it possible, but not guaranteed, to try to make a connection.
