In article , "Bill Denton"
writes:

Also, AM stations require a ground system, which is not required for FM or
TV stations. The ground system consists of a series of wires, buried
underground, each the length of the tower, and located at 10 degree (IIRC)
radials emanating from the tower base. Imagine the radials extending out
from a VOR every 1 degree, although these are not actual, physical, wire
radials. But for AM radio, these are actual wire radial, extending out every
10 degrees from the tower, with each radial the same length as the tower.
And you can't build anything on top of these radials, other than a small
transmitter building, as it will disrupt the signal. Which is why there is
always a large open area around AM towers that is not necessary, from a
broadcasting standpoint, for an FM or TV tower.

I don't know where you got this from. If you look at the arial pictures of the
KFI tower, you'll find that it is barely 100 feet away from industrial
buildings.

John