MeshCore/Meshtastic Antenna (915 MHz)

This is a simple form for building a directional antenna for the 915 MHz band.  It's based on the DK7ZB "Quadlong Hentenna" (https://www.qsl.net/dk7zb/Quadlong/Hentenna.htm), but scaled for 915 MHz and turned sideways for vertical polarization.

The goal was to make it possible to create a directional antenna without drilling, sawing, or having to make multiple trips to the hardware store/ironmongers/Bunnings (insert as appropriate).

All you need is this printed form, some #18 solid core hookup wire, and a pigtail (coax connector with a suitable length of coax cable).  I usually buy a pre-made cable with connectors on both ends and cut it in half to get two pigtails.

I've included the OpenSCAD "source code" so that you can adjust the design to suit different frequencies, wire gauges and coax diameters.  The included STL file was for intended 910.525 MHz (North American MeshCore) but actually resonates nearer 900 MHz.

I recommend PETG.  No supports are required.

Hopefully the pictures make the assembly reasonably clear.

Cut the #18 wire to exactly fit in the grooves, then press-fit it into place, adding a bit of glue if necessary to keep it in place.  Note that the wire for the two reflectors on the back of the antenna pass all the way through the body of the form.

Insert the coax cable into the cylindrical housing from the rear, strip off a bit of insulation and solder short pieces of hookup wire to the coax.  Protect the joints with heat shrinkable tubing (optional).  Press the short pieces of hookup wire into the grooves above and below the cylinder as shown, gluing if required.

Using a craft knife, strip the insulation from the hookup wire where it passes through the half-circle cutouts in the form.  On the short side of the form, solder the two wires together to form a loop.  On the long sides of the form, solder the short pieces of wire coming from the coax to the loop.

Press the small circular cap in place over the cylindrical housing and you're done!

This is a skeleton slot antenna, so the polarization will be vertical when the long side of the loop is horizontal.  Maximum radiation is in the direction from the vertical reflectors towards the loop.