The Old Journal can be found inside the locked room in the Old Shed in the Swamp. It is burned and barely legible, though it does seem to be referring to the Radio Tower.
"The pages are glued together, creating a rotting chunk of paper. On the bottom of the note, it reads: "Radio tower - door 21, 12 PM. Kowalczyk, Trzcinkowski, Stelmaszczuk, Zieliński". At the top, I can only make out the words "Devil horns - orga..."