Stalker: Call of Pripyat → Radio Interference, Unknown, and the "Skat" Squad
Radio interference
We go to the courtyard just south of the school, search the soldier's body, and take the explosive device with a timer. After that, we contact Kowalski by radio. The lieutenant colonel says they've located the signal's exact location—it's coming from the kindergarten. We head there, plant the explosive device on the door, and quickly retreat to a safe distance.
After the explosion, we can enter. We go up to the second floor and go to the west wing. There will be a poltergeist there. Once we reach the west wing, we'll see the installation—it's the source of the interference. We receive the task of destroying it. We throw several F1 grenades there.
After destroying it, we hear a knocking sound coming from below. We need to investigate the source of the sound. We open the refrigerator and find the missing soldier inside, then go talk to Kowalski.
Unknown and the Stingray Squad
We follow the signal south of the dorm. When we arrive, the signal starts to move—we run after it. It turns out the signal was coming from underground. Now we need to return to base. Once we're there, we watch a cutscene: a gunner comes to us, explains the general situation, and explains why the helicopters crashed. All that's left is Evacuation .
Source: stopgame.ru
See also:
Call of Pripyat: Quest "Surviving Monolith"
Call of Pripyat: Quest "One Shot"
Stalker: Call of Pripyat - Quest "Runaway"