868Mhz LoRa Meshtastic Yagi-Uda directional antenna

This is 868Mhz LoRa Meshtastic Yagi-Uda directional antenna with 6 elements and square boom. Actually calculated for 869Mhz, since this is closer to real meshtastic working frequency in UE). Dimensions were taken from widely-known DL6WU Yagi-Uda antenna online calculator. Theoretical gain is 11.1 dBi (approx.).

How I Designed This

Recipe for antenna dimensions from the calculator

The calculator
Long-yagi DL6WU

Driven element (dipole) form: Straight
Element shape: Round

Frequency f: 869 MHz
Wavelength λ: 345 mm
Element diameter d: 1.7 mm
Boom side D: 10 mm

Total number of elements: 6
Boom length: 319 mm
Gain: 11.1 dBi (approx.)

Reflector length R: 168 mm
Reflector position R = 0

Dipole length F: 162 mm
Dipole position F (R-F): 69 mm
Gap at connection point g <= 4.6 mm

Length D1: 151 mm
Director position D1 (R-D1): 94.9 mm
Distance F-D1: 25.9 mm

Length D2: 150 mm
Director position D2 (R-D2): 157 mm
Distance D1-D2: 62.1 mm

Length D3: 148 mm
Director position D3 (R-D3): 231 mm
Distance D2-D3: 74.2 mm

Length D4: 146 mm
Director position D4 (R-D4): 317 mm
Distance D3-D4: 86.2 mm

Elements on a dielectric boom.
Boom-correction is not taken into account.

If you re not sure about wire dimensions or placement, take a look at DL6WU_yagi_antenna_cad_v8_with_wires_pre_boolean.3mf file in this project. This is complete model of antenna with wire elements. You can check length of wires up there. Of course do not 3d print this file :)

Preparation

I used copper wire with a diameter of approximately 1.7mm. If you have a different gauge wire, you'll need to slightly modify the model and recalculate the dimensions in the calculator.

The Wire

The wire needs to be straightened and cut to the lengths indicated above. Then, thread the individual wires through the holes in the 3D printer (the holes are already spaced correctly). You may need to manually widen the holes slightly to allow the wire to pass through with a little resistance. After perfectly centering the wire relative to the antenna axis (a caliper and a square will come in handy), I pre-attached the wire using cyanoacrylate/superglue. After drying, I re-attached the joints with two-part resin glue.

Signal cable

I initially secured the antenna cable with cable ties. Then, after cleaning, I soldered the shield and signal cable to the two "F" wires, i.e., the antenna's active elements. I also secured the soldering point with heat shrink tubing. The photo shows the antenna cable installation before soldering.

Here is the final connection after soldering and securing. Remember that there is a gap in the wire at the active element/dipole (effectively two wires on the right and left): Gap at connection point g <= 4.6 mm. It's best to check this gap with a caliper; for convenience, there's a special window for this in the 3D model.

All togheter

I joined the two parts of the 3D print using two-component resin glue. After drying, I painted the entire piece with a layer of clear acrylic varnish. The varnish will protect both the copper and the solder from weathering.

Worth watching

Watch video - not mine!
My antenna is different from the one in the video, but it is worth watching the video itself because it contains a lot of interesting information about the construction of such an antenna.

The roof

You can attach the antenna to the mast using cable ties; there are two slots in the foot for this purpose. Usually higher is better.

Results

In my area, the furthest signal I received was over 270 km away. However, everyone's results may vary depending on the terrain, radio, cable length, precision of construction, etc. I've only been testing my antenna for a few days.