Yet another 868MHz Moxon antenna
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Moxon antenna build for use with Meshtastic devices working in 868 MHz European band.
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Another Moxon antenna. I don't trust other designs and decided to design this antenna to my own specifications.
This antenna was designed for PETg plastic, so the dimensions differ from those given by the calculator for a frequency of 868 MHz (869 MHz to be sure, but it has a good bandwidth and a tunability).
Printed with 0.2mm layer height and 40% infill.
To make the antenna, you'll need 1.5mm diameter copper wire without insulation, RG-316 cable, heat-shrink tubing, and T-7000 adhesive and some paper clips.
First, take the copper wire. It must be formed and placed into the grooves on the base. The edges must be flat for maximum efficiency, meaning the cutting marks should be filed down. After installation, the radiating element is nipped in the middle, removed, and then filed so that the gap between the two parts is within a millimeter when applied to the printed things.
For the RG-316 cable, it's best to make a balun: cut a piece of the same RG-316 cable approximately 70 mm (or longer) long and carefully remove the braid. Next, stretch the previously removed braid over the main antenna power cable. It should shrink to about 59.6 mm. Stretch it so that the end of the cable that will be soldered to the active elements is exposed by about a centimeter. The lower part of the braid needs to be soldered to the cable: to do this, carefully remove the outer insulation from the cable with a razor blade in a 4 mm wide ring, and then solder it to the outer braid. Conceal the resulting structure with heat-shrink tubing.
Don't be afraid to solder it: this cable has PTFE as the core insulator and FEP as the outer insulator, both of which are thermostable and very hard to melt with 300°C on a solder.
So, the length of the outer braid should be equal to 59.6mm!
Expose the upper part of the cable: solder the cable braid to the left element, and the central core to the right element, then lay it in the printed base. Right element marked with a hexagon on the top element: orient the antenna so it will be on the upper side when placed vertically. It is unnecessary, but preferred.
Adjustments may be necessary if the Smith chart on your VNA isn't perfectly aligned when the two plastic parts are joined: you'll need to file down the curved parts of the radiating elements just a little.
For final assembly, apply glue to the grooves on the top plastic part (see photo). Apply glue to the flat surfaces with the four holes. Also, apply glue to the areas where the cable will be installed on both parts. Finally, press the halves together, secure them with paper clips, and let them dry for 24 hours.
Attention: the third photo is a test prototype, so lengths look odd, but this picture gives a clue about cabeling, wiring and glueing. The copper wire is placed into the grooves completely, without gaps.
Enjoy!
UPD_1: Added a simple hinge.
UPD_2: Widened cable channel. Lots of complains about hard times of pressing the cable in.
UPD_3: Added a simple adapter for the foreign Moxon design with a cool-looking stand...
UPD_4: Adjusted hinge a bit. Added long stationary part (+100mm to its length). And here is a nice screenshot of the antenna with hinge.