http://www.fybush.com/sites/2005/site-051021.html

In 1949, the station (by now using the calls KNBC) replaced one of the
old towers with a 550-foot guyed tower, the same one that's still in
use 56 years later as the main tower. This is a most interesting tower
for several reasons: first, it's unusually short for a class I station
on 680... and second, because it's got an insulator about two-thirds
of the way up the tower.

Yes, it's a sectionalized tower - and one with a top hat on the upper
section, to boot, to give the tower a little more electrical height in
lieu of the physical height it couldn't achieve because of the nearby
San Francisco International Airport.