Coax Trap Form

thingiverse

Human: # Coax-Trap-Form\r\nParametric OpenSCAD model for creating coil forms for coax-traps used in wire antennas.\r\nThe official home for these files is [https://github.com/SmittyHalibut/coax-trap-form](https://github.com/SmittyHalibut/coax-trap-form)\r\n(Sorry Thingiverse, you're just a snapshot of my work at a given time.)\r\nFor the newest versions, look to github.\r\n\r\nThingiverse pictures show various parametric options. These are examples; you can make any form you want:\r\n1. RG8/X, 6.25 turns, 3.1in diameter form (This is the only STL included.)\r\n1. RG58, 6 turns, 2in diameter form\r\n1. RG58, 6.5 turns, 2in diameter form\r\n\r\n# Electrical Design\r\nElectrical design from the 2015 ARRL Antenna Handbook\r\npage 10-15, section 10.2.2, "Five Band W3DZZ Trap Antenna"\r\nThe goal is a trap resonant at 7.2MHz, which natively builds a 40/80m\r\nantenna. But the series capacitance in the trap allows the total antenna\r\nlength to resonate at 20, 15, and 10m as well, at higher harmonics.\r\nThe idea is a 5 band antenna with only one pair of traps.\r\n\r\nThe book shows two designs:\r\n1. Traps: 60pF, 8.2uH, 22' outer wire length\r\n1. Traps: 100pF, 4.9uH, 21' outer wire length\r\n\r\nBoth have 32' inner length, and are fed with 75ohm.\r\n\r\nMy goal is to make these traps using the coax trap design discussed\r\nlater in the chapter.\r\n\r\n# My Antenna\r\nUsing: https://www.qsl.net/ve6yp/coaxtrap.zip coax trap calculator,\r\nand C/ft numbers for coax I had on hand (RG8/X and RG58), I wasn't\r\nable to make a coax trap with the exact values above; all common coax has\r\ntoo much C/ft to get down to 100pF. The best I could do was with my\r\nRG8/X, down to 137pF and 3.575uH, 6.25 turn on a 3.1in form.\r\n\r\nThe included STL is that form, with holes in the right places for coax and attachments.\r\nPrinted vertically like a tower, **THIS WILL NOT BE STRUCTURAL!**\r\nMy intention is to feed the antenna wire through a nylon rope so the\r\nrope is tensioned, but the wire is not. The trap structure will just be loosely\r\nhanging from the wire ends that stick out from the rope an inch or two.\r\n\r\n\r\n\r\n# Your Antenna!\r\nBut the OpenSCAD file is entirely parametric. \r\n\r\nInstall [OpenSCAD](https://www.openscad.org/), open the `.scad` file,\r\nand change the parameters:\r\n```\r\n// Calculator: https://www.qsl.net/ve6yp/coaxtrap.zip\r\nform_diameter = 3.1*in2mm;\r\nnum_turns = 6.25;\r\n// RG8/X, LMR240 = 0.242\r\ncoax_diameter = 0.242*in2mm;\r\n// No 10-24\r\nbolt_diameter = 0.200*in2mm;\r\nform_thickness = .200*in2mm;\r\n```\r\nOpenSCAD uses millimeters, but the coil form calculator uses inches.\r\n\r\n# Show me your antenna!\r\nIf you build something with this model, I'd appreciate it if you sent me\r\na picture and/or description of what you built. You can reach me on Twitter at [@SmittyHalibut](https://twitter.com/SmittyHalibut).\r\n\r\n73 de KR6ZY, @SmittyHalibut\r\n-Mark