Customizable RF Coax Air Choke for HAM Radio

thingiverse

A fully customizable form for coils of coaxial cable for HAM radio allows for creating an "RF air choke". The form is configurable, meaning it can be adjusted to accommodate coil diameter, loop count, coax wire diameter, and optional center cutout diameter. An air choke can certainly be created by wrapping coax around a regular cylinder such as PVC, but flat spots may develop where the coax is pressed against the PVC and cause damage. This design, with a race for the coils in both the center form and retainer sections, should result in less deflection of the insulation layer inside the coax cable over an extended time period. Additionally, it allows the mean coil diameter to be configured to any size that fits on your 3D printer, versus being limited to available sizes of PVC/etc tubing. Note that the retainer pieces are meant to be attached with nylon wire ties, and they are numbered since the coax will be at a different height in each one. Default parameters are for six 200mm loops of Belden RG8 9913F7 coax just as an example, but please customize to your own cable size, loop diameter, and loop count. It is recommended to use "split" operation in your Slic3r program to reposition the "retainers" before printing. An updated scad file was added on 3/28/21 to include a coil_pitch_factor parameter for adjusting pitch as a factor of the wire diameter.