Long story short, I've typed this once and it just disappeared when hit submit?
Anyway in the late 70's I built a jammer for my brothers 930. It worked, very low power as all you have to do is overcome the radars return signal and that is very weak. Cool jammer as you could determine the speed the LEO radar would see by varying the output freq slightly. Your actual speed was irrelevant. Back then there was only X band. Now there are at least 4 seperate bands, I think. This would either require 4 xmitters or maybe you could "Barrage" jam them all. Barrage jamming requires a LOT of power, maybe enough to be unhealthy. With a jammer you have to be very fast on the xmit button. You shouldn't drive around xmitting as you and everyone around you would be blind as your xmitter would set off all of the local radar detectors. I used an Escort radar detector to trigger the jammer. Once triggered the thing went closed loop and would stay on until you turned off the detector. Of course any false signal would set it off as well. kinda annoying actually.
Yes it was illegal even back then. Don't know how hard it would be to build one now.
The most fun I had with the thing is at first I had it mounted in an old Ford pickup. I would drive around with the freq. ramped up (the higher the freq= higher speed on an approaching vehicle) and watch as the LEO's comic alarm would go off and he would start rapidly scanning for that very fast vehicle that didn't exist.