This is the best omnidirectional 2 Meter antenna I have ever encountered.
The highest cone is to form the lower half of a half wave vertical element.
The lower cone is a decoupling sleeve for the antenna mast.
If you find one of these at a hamfest for $20, buy it. It works great, and
a lot of people do not know what they are. You could actually build one
from aluminum flashing and a mag mount. The original manufacturer is out of
business and the Isopole is no longer available new.
I will upload photos of my restoration work on this one, but the data sheet
is provided here on my webpage for you to do your own work, should you be
lucky enough to find one of these.