F360 Parametric Coax Trap Body

Please note that this is a work in progress.  Changes may be made at any point.

This model is a winding body for a coax trap used in amateur radio antennas.  The Fusion 360 model source is included and makes use of user parameters to control diameter, height and hole placement.  When used in conjunction with a coax trap design program, the user can achieve a custom design with optimal length to diameter ratio for the specified resonant frequency and coax type used.  

The major benefits are the ability to tailor winding body diameter to accomodate both coax type and desired frequency and the automatic placement/generation of starting and ending cable holes based on winding turn count, including fractional turns.

The TrapBody model is the coil winding form.  Bolt/screw holes are round, coax holes are oval. The BodyCap or InsetBodyCap model can be used to cover the TrapBody ends.  The endcap models are ventilated in a fashion to help avoid water build up and insect nest building. 

The strain relief models can be used to reduce strain on the wire antenna electrical connections.  The wire version captures the wire for a direct connection, the belay version allows use of a quick link or cord to anchor the TrapBody.

My emplementation of the trap design is based on using two 5mm stainless steel screws, with stainless steel washers, one set at each end, for making the electrical connection to the antenna. Stainless steel or nonferrous metal is recommended for the hardware if significant power is used,  in order to avoid eddy current heating. My intent was to use crimped ring terminals at wire ends for connection at the screws.  I am using PETG for printing.

The TrapBody product includes embossed information about design frequency and winding turn count. This feature requires installation of the free Autodesk app store add-in, “ParametricText”:

https://apps.autodesk.com/FUSION/en/Detail/Index?id=2114937992453312456&os=Win64&appLang=en

The STL files supplied were created for building a coax trap resonant at 7.1Mhz, using RG400 coax, and a winding body diameter of 6.75 cm, providing a band width optimal length/diameter ratio of 0.45, using 6.57 turns (59.88in of coax).

The trap design is similar to this:

https://www.qsl.net/ve6yp/CoaxTrap.html

Installing the associated program may take some finesse if using windows 11, but can be done. Google “windows 11 cannot run installshield app” if you have issues.

A web based program can be found here:

https://www.k7mem.com/Ant_Trap_Antenna.html

More related info:

https://www.w8ji.com/traps.htm

 https://buildthings.wordpress.com/ham-radio-20-meter-short-40-meter-coax-trap-dipole-antenna/

This is a work in progress.  The structure looks correct for the parameters provided, but use your best judgement as to how well it might serve your requirements. Do a sanity check on hole placements.  I am still waiting on components to finish my first build with this model.

The model source reflects a design with features that changed multiple times from the initial (simple) product & the lack of organization in the workflow/timeline reflects that.  At some point I may redo this from scratch for a better organized product.

EDIT 4/29/2023: Added inset version of  endcap