Two rookie Air Force engineers, using only what they could find out over the Internet or buy at an electronics swap meet, managed to build an impressively powerful jammer that could block military satellite communications over a considerable area. The engineers spent only $7,500 putting their system together, including a gasoline-powered generator. One analyst noted that with very little more effort, a mobile jammer could be built that would block GPS signals, making US precision GPS-guided bombs useless. The US Air Force discovered this problem through its Space Aggressor Squadron. This small unit, based near Colorado Springs, is an intelligence section which searches open sources for information on how to build systems that could interfere with US military and space operations.--Stephen V Cole