An enclosure for a Jpole antenna, I made mine for 869mhz, but have included the Fusion 360 files if you wish to resize the top section to accomodate differnt lengths.

For mine the copper I had was about 1.4mm diamater, it came from twin and earth cable.

SMA male connector came from a SMA male to IPX pigtail.

Use a calculator to get in the right ballpark: 

https://www.omnicalculator.com/physics/j-pole-antenna

Some rough instructions

• Cut a secton of copper wire and use something to bend around, so that there is about 4mm gap.
  • Give your self a few extra CM for each length, so you can tune with.
• Snip the SMA male with about a 1-2 cm
• Feed through the bottom section
• Strip to expose the shielding and core, solder the core to the long section and the sheilding to the short section, about 8mm from the bottom.
• use a bit of hot glue around the joint and glue on the mid section of the tube
• Check it out with the SWR meter and trim. Make sure to take your measurements with the top section on.
  • when trimming, I was taking about 2.5mm of the long section for every 1mm I took of the short section.
• When she resonates, glue the last section on 

Some important notes

• I found that once I put the top cover on, it shifted the resonant frequency lower significantly. Meaning I had to “Over trim” the antenna, but this corrected after adding the top piece of the enclosure.
• I have provided the measurements of mine, however this could differnt depending on the material, colour etc.
  • I used Creality Clear PETG.