This is a groundplane antenna jig you can use to make an antenna with a short pigtail of feedline. It fits over regular 2" central vac PVC tubing, or you can print your own tube. Inside the tube there is a board to mount a RAK 19007 base board with accessories mounted, I am using a RAK 13800 with 19018 for POE to my meshtastic node. The inspiration for my antenna jig was this one https://www.thingiverse.com/thing:4839040
Once your antenna is made and you've got a connector on the pigtail, mount the radio on the board and into the ring. the ring keeps the board from moving around inside the tube. There are two board sizes provided, depending on the length you need.
The plug in the bottom was an easy way I found to get a cable up into the tube and provides a customizable fit for the cable you're using to keep the weather out. The idea for using a plug came from https://www.printables.com/model/305015-tbeam-outdoor-enclosure
I used this calculator for element and radial lengths for my antenna https://m0ukd.com/calculators/quarter-wave-ground-plane-antenna-calculator/
The author marked this model as their own original creation.