The Radar Range is found
*** Spoiler - click to reveal ***on the last level of the game where you're sealing sally into the vents. Simply seal the first with Liz, then move into th next room. Pick up the Audio Log in the broken lift and open the door on the left side of the room. You'll be in a room with a woman talking to some dead people in a Bistro. Then there'll be a locked code door which the audio file contains (3958).
If you hold down the trigger and aim at an enemy they'll start to glow red when hit. Hold it enough and they'll pop. This also cumulative so you cook 5 individual enemies, not all at once.