Tunable 433 MHz Moxon LoRa/Meshtastic antenna

Moxon antenna created to be easily tuned with VNA

NOTE: It only makes sense to download and build it if you have VNA and know how to use it, without it you won't be able to tune this antenna.

For most cases the TC3EC Moxon Antenna (https://www.printables.com/model/1313115-tc3ec-433mhz-moxon-antenna) is sufficient and yelds good results, not requiring the tuning and VNA. But if you are a nerd like me and want your numbers on the VNA charts to be nothing but perfect — welcome to using this antenna, it makes it easier.

Also, unlike TC3EC antenna, all parts of this antenna fit to 220x220 printbed.

Wire lengths: use the Moxon calculator values shown below for starting point:

Tuning

Design allows to «tune» 3 parameters on the fly, while attached to the VNA:

chop small pieces off the driven elements (symmetrically on both sides)

chop small pieces off the reflector (symmetrically on both sides)

distance between driven elements and reflector by moving a sliders and then when best position found, tighten it with M3 bolts. Use some washers. You can use nuts on the other side, or just screw into plastic.

Usually you can chop couple of milimeters from reflector and leave it, then only chop small pieces from driven element and move reflector around. Make sure to put your hand away from the antenna before taking measurements. If you touching antenna while measuring — results will be skewed.

A bit fiddly to get the reactivity and SWR perfect, but at least it allows to do it. I was able to move point on the Smith diagram right to the center, and make SWR dip to 1.05 while at the 433 Mhz frequency.

Printing

It might be a good idea to print tests first to see if sliders fit and slide as needed, and if your wire clips in into the wire fit test. It should clip in, with some force applied (with a flat screwdriver or something like that to push it all the way in)

Wire: Copper with 1.7mm diameter (or 2.5mm^2 section) when stripped, some variation allowed.

Cable: I'm using RG58, model is tailored for it.

Choke: I'm using ferrite clip with NiZn compound. Ugly Balun seem to be ineffective at those frequencies, and impossible to do with RG58 anyway.

Material: if you plan to use it outside, then avoid PLA. I'm using PETG.

Supports: not needed, just print front and back in different orientations:

Front — wire slot up

Back — wire slot down

Other hardware:

2x M3 bolts

2x M3 washers (nylon preferable)

2x M3 nuts (optional)

3X M5x15 bolts to secure antenna to links and base

3X M5 nuts

Couple of 2 or 3 mm wide cableties to secure the cable

Some screws or cableties to secure base to something