A close up view of the SO-239 coaxial cable connector which is mounted on an aluminum plate.  The plate is mounted over a hole cut in the rear of the tube enclosure.  The plate is screwed to the back of the case with eight screws to ensure proper RF shielding.  The brass screw seen to the right of the connector is for connecting one of the balun input wires, the other wire goes to the center pin of the connector.