If you care to examine what is available on the web for relatively little effort you might be astonished at the breadth and variety. You could do worse than to start here
A newbie's guide to UAVs - DIY Drones.
Searches on terms such as "ardupilot" and UAV will yield lots of information which has clearly escaped several of the contributors here. There is, for example, a company in Buenos Aires which is marketing a fixed wing UAV with a 20Kg payload and a maximum weight of 87Kg. They're asking US$12,600 for the airframe without electronics. It doesn't take much imagination to see to what nefarious purposes this could lend itself.
GPS jammers have been deployed by military and security forces, and knowing the frequency and feeble power of the transmissions should be readily constructed by anyone interested and energetic enough to do so. Jamming 2.4 Ghz would be much more problematic, as it is the current standard for WiFi, and pretty much any domestic and industrial wireless communication, including medical devices etc. In fact if I planned to use a UAV as a terrorist or merely mischievous device to interfere with aviation I think I would equip it with a GPS device and autopilot for primary flight control. To alter the flight path I would use radio control to revise the GPS co-ordinates.
I have not, and never will have any plans to put this into action, but I think we should all be aware of the possibilities.
