I encountered an "instant on" K, yesterday targeting other cars a full minute or so before I reached his location in the median of a 4 lane hwy (my speed was approx 65 mph): a lot of turns, woods, etc between the LEO and I, but the signal was clear as a bell every time.
I also encountered a constant on Ka, initially from about 4-500 yds perpendicular from me, entering a two lane road, and turning into the same direction I was travelling at 2-3 bars. I followed him for several miles, and could generally keep the Ka signal, although only 1-2 bars with no cars approaching. When another car approaching the LEO fom the front my STI went to full strength (probably from the radar return coming back to the LEO, and then to me). Throughout I remained 4-500 yds behind the LEO.
I passed a Spectre equiped car twice (deliberatly) which was parked in the median facing my lines of traffic, and some 10-15 yds from the side of the road-no reaction.