Hi David, You can better determine what size tower you need by first finding your HAAT. The FCC's website has a great calculator for this at: http://www.fcc.gov/mb/audio/bickel/haat_calculator.html It's not a graphic program but it will give you a chart of the altitudes surrounding your location. You will need to know your base elevation, then you can plug in various antenna heights to see what the HAAT is. -- 73, Don, NN8B