John W6IPA created a 3D project for the 20m portable antenna coil. Its on Thingiverse
I used the Buddipole Featherweight whip that has a 1/4 thread on the base. These antennas are cheap.
Get a couple of BTS IT adapters as it will allow a FW whip to fit onto a 3/8″ stud mount.
You dont need it for the project but its useful to create other antenna designs.
I use the BST IT adapter at the base of the antenna and a mount in my design
You do need a counterpoise to get best SWR and its possible to lower the whip elements and shorten the counterpoise for use on 17m and 15m
see ya’ll at Xenia at the Buddipole BUG Meet Up