"But the German radar detector receivers used supperregenerative detectors,which radiate a weak signal." Don't know whether this is apocryphal or not, but I had heard from a former USAF EW tech that the VC in Viet Nam in the early days figured out how to make U.S. field superhets' LO "howl" , giving away qth, causing some units to switch to TRF technology. Gil NN4CW