That coil is a choke made from coax, and it extends up into the antenna.I see that. That extra below the coil and feed point is for mast attachment?
The actual feed point is about half way up the antenna and uses a shorted impedance matching stub inside the fiberglass, and a capacitor to couple the top section.
That's why they call it a center feed antenna.
It doesn't need radials because both sides of the antenna are already there.
This is much different from the matching on the bottom of the imax antenna.
Sirio is more realistic about there gain figures than Solarcon ever was about the 99 and the imax with 9 and 12 db gain.
73
Jeff