Added a readme
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3DP-QFH
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3DP-QFH is a quadrifilar helicoidal antenna for 137MHz,
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build out of 3D-printed connection elements, PVC-tubing and welding rod.
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![dimensions](images/qfh_3dp.jpg)
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The dimensions have been calculated using the [calculator](https://www.jcoppens.com/ant/qfh/calc.en.php) by John Coppens.
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![dimensions](images/QFH_dimensions.jpg)
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The 3D printed parts are designed to account for all the odd distances,
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allowing the PVC parts to be cut to nice full centimeter lengths.
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The welding rods are copper coated steel which provides stability to the antenna,
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while it is still possible to solder the coax to them.
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BOM
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---
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* About 2m of 15mm diameter PVC-Tubing
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* 5 screw terminal blocks (aka. [Lüsterklemmen](https://commons.wikimedia.org/wiki/File:Screw_terminal_with_crimped_wire.jpg))
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* A few meters of RG316 with your preferred connector at one end
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* 8 WIG welding rods 3mm diameter (and longer then 50cm) or any other type of sturdy conductive wire
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* Epxoy glue
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* 3D printed parts
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Construction
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------------
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1. Print the parts
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* one top part
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* one middle part
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* one bottom part
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* two cap parts (stl contains two different types, print twice)
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2. Cut the PVC-tubing according to [lengths.pdf](lengths.pdf)
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* one piece 32cm
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* one piece 29cm
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* two short loop supports 13cm
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* two long loop supports 14cm
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3. Glue the top part into the 32cm piece
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4. Glue the bottom part into the 29cm piece
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5. Mark the upper side of the middle part (same orientation as in the stl file)
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6. Glue the short support tubes over the upper two arms of the middle piece
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7. Glue the long support tubes over the lower two arms of the middle piece
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8. Glue the middle piece between the other 2 assemble parts,
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ensure that arms for the short loop on the bottom piece (the upper two) are
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rotated 90° with respect to the support arms.
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Also make sure that the arms of the top piece line up with the support arms.
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9. Plug the endcaps into the support arms, without glueing them in yet.
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Make sure to plug the larger ones into the shorter support arms.
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10. Bend the welding rods. The dimensions are not too critical.
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* bend 4 pieces after 15.4cm for the long loop
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* bend 4 pieces after 14.6cm for the short loop
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11. Insert the pieces and cut longer ends at the support arms.
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Make sure your helix turns counter-clockwise.
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12. Use the screw terminals to connect the pieces inside the support arm caps and the bottom piece
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13. Glue the support arm end caps in place
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14. Feed the coax through the tubing from the bottom to the top
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15. Strip the coax and solder it to the welding rods according to the following schematic.
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![top wiring](images/qfh_top.jpg)
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(Schematic taken from [https://www.jcoppens.com](https://www.jcoppens.com/ant/qfh/adapt.en.php))
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A and B are the connections of the long loop.
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You can use a piece of PCB or solder directly to the rods.
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16. Test your new antenna
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