Sirio GP430LB autopsy
The center pin is connected to the shaft with the two bolts and the brass tube. The end of the brass tube is connected to the antenna's upper aluminum cylinder (the one I disassembled to take those pictures), with the side Philips screw.
Both copper / white plastic tubes are connected to the flat screws at the top of the antenna, but only one of them is connected to the ground through the thin copper wire & coil. The other one has no electrical connection between its two copper elements.
Below the bandwidth @ 1.5:1 SWR measured with my VNA:
As noted on the pdf title, the antenna is not used in the best conditions, so you can expect best performances when mounted on top of the mast with no other parasitic element in a near area (compared to the wavelength).