 Because each antenna was aimed to be sensitive primarily in a single direction , the length of the blips depended on the position of the target relative to the fighter . For instance , a target located 35 degrees above the fighter would cause the signal in the upper vertical receiver to be maximized , causing a long blip to appear on the upper trace , and none on the lower trace . Although less sensitive directly forward , both vertical antennas could see directly in front of the fighter , so a target located dead ahead caused two slightly shorter blips , one on either side of the centreline . 
