Tube Cap for wifi Antenna

Hi,

I design some caps for creating cheap outdoor wifi 2.4ghz antenna.
Antenna has been created by Martin (https://martybugs.net/)
Antenna is made of :
1 piece of Electrical PVC pipe (Diameter 20)
1 blind cap
1 BNC cap
1 copper electrical wire 2.5mm²
1 Mount panel BNC connector

Marty's tutorial for calculate the antenna can be found here:
https://martybugs.net/wireless/collinear.cgi

Loop are created with 12mm drill bit
cap are glued on the tube.

Adjustement of cap are quite