Broadcast tower LP8
A radio antenna and a generator are found enclosed behind a metal fence; the latter's switch can be turned on to emit Signal Echo Foxtrot. The sealed cistern entrance is at the base of the hill on the northeast side (facing the monorail / highway ruins).
Inside the sewer chamber, there is a copy of Big Book of Science.
This is a random encounter location. The exact spot is on the north-northwest corner of the gate that surrounds the broadcast tower, and will be triggered within a radius of approximately 20 - 25 running strides.
Broadcast tower LP8 appears only in Fallout 3.