Do I need an outside GPS antenna?
Generally, yes. If you are in a single story wood framed building you will probably be able to track some satellites with the antenna indoors, but performance will be degraded. Buildings with a lot of metal in their frames (or foil-backed insulation in the walls and ceiling) make extremely effective shields. Even so, placing the antenna next to a window will generally prove to be sufficient for basic testing. Because of the orbital paths of the satellites, users in the Northern hemisphere should avoid North facing windows since satellite visibility will be poor. Users in the Southern hemisphere should likewise attempt to avoid South facing windows.