The sleeve makes the folding joint far stiffer than it was, but it still slides up and down on the antenna so I can fold it if I need to (for instance) park in a structure that has a low clearance (one of the advantages of a small car is easy parking, after all). Each piece is a snug fit over one section of the stepped base of the antenna, and some of them have a notch (looks like a keyway) to clear a pair of setscrews that lock the whip into the folding joint. In order to make it 3D printable on my Ender 3, I made it in four pieces (too tall and the wobble it gets from the movement of the bed causes a failed print). My solution was to use FreeCAD to design a plastic sleeve to reinforce the folding joint on my antenna. Problem is, wind loads (those coils I mentioned are significantly fatter than the main whip) combined with vibration are enough to cause the antenna to spontaneously fold at highway speed - which does nothing good for either reception or transmission of the radio signal (there's a huge loss if the transmitting antenna is perpendicular to the receiving one, and repeaters have vertical antennas). The folding joint on the antenna is made to automatically "break" if you forget to fold the antenna before passing under a low clearance, to prevent actual breakage or bending the whip. What's this got to do with 3D CAD and 3D printing? Since it mounts vertically on a car, either on the roof, edge of the trunk lid, or a fender, the one I bought also has provision to fold down as needed for parking under a low overhead - though because I drive a small car (Ford Fiesta sedan), the clearance a large pickup truck with off-road setup needs for its roof is enough for my antenna without folding. This radio needs an antenna, of course, and since it's a quad-band radio, the antenna needs some joints and coils, rather than just being a length of stiff wire or rod stock. I've been a ham radio operator for a couple years at present, the only working radio I have is in my car.
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