To open the door that requires a radio frequency, you must capture a guard. Hold the knife to him to get the information by pressing L3 (145.86). Call that while standing in front of door to open it. You should hear a click. Once inside the door, the very powerful Skorpion (includes laser sighting) can be found in the far northeast of the room, along with ammunition. Note: The room can only be entered through the door located to the east. The one to the west does not open until after the east door is opened.