A British firm has perfected a method for using cell phones to detect stealth aircraft. It was noted that the radiation from cell phone calls bounces off the bottom of stealth aircraft. A British firm developed a small dish that can detect the reflected signals and plot the position of the stealth aircraft to within ten meters. A set of cell phone antennas and a detection dish cost less than $200,000, can be carried in a truck and can cover several hundred square miles. Each base station can be 20 kilometers away from another to form a detection net. Thus a large area can be covered inexpensively. It's possible that the Serbs used such a system in 1999 to detect and shoot down a F-117 stealth aircraft.