Illicit kit imported into Europe from China operates on the same frequency as GPS satellites to drown out timing signals and confound in-car devices. Because of this in-vehicle systems are unable to either determine their position or report in to vehicle tracking centres in cases where cars or lorries registered with GPS-based tracking technology are stolen.
Not managed to get my hands on one but I've seen one in action. Without getting too much into it, GPS jammers have a lot more use than just jamming car tracking.
The principle behind the jammer is that you create a small radio transmitter that sends out the same kinds of signals as the satellites. Military GPSs have extra code to ignore a randomly strong signal but Civilian ones don't usually have any of this jazz.
Most GPS handheld units do show the receiver strength of signals coming from different satellites, so a "jamming device" would have that fingerprint of an abnormally strong signal, but that's it.
>>8313 GSM and GPS frequencies are a long way away from the normal 433Mhz radios that you can buy. You need a very good oscilloscope and some other test equipment to knock one of these devices up from scratch. Better to bend something.
You would have more luck I think bastardising something like one of these modules :-
Really not trivial though unless you're fully up with electrickery and radio. Would probably work out much cheaper/easier to try and buy one from China.
Some of the Arduino stuff mentioned on that page (and here by some others) looks really interesting too.
