Moxon antennas: awesome, easy to build, high gain Yagi alternative

As you may have noticed, I'm really enthusiastic about operating low power (QRP), with an emphasis on Summits on the Air (SOTA), along with the other "OTAs" (POTA, VOTA, and so on). In many cases, weather conditions make HF operating difficult, particularly in high wind situations where erecting a wire antenna or even a vertical nearly impossible. In those cases, particularly when you're operating within 100 miles of a metropolitan area, VHF simplex is generally the best bet for setting up quickly and getting the minimum number of QSOs to qualify as an activation (4, in the case of SOTA). Note that repeater operation does not qualify as a valid QSO, at least for SOTA/POTA. 

As you probably also know, trying to get any range out of a 5-watt handheld transceiver (HT) with a "rubby ducky" antenna is a long shot at best, since those antennas are basically just dummy loads in a flexible form factor. So one needs a higher gain, preferably directional, antenna, in order to reach people at longer distances. 

Many people have successfully built and deployed small Yagis for this purpose, which are a great choice except for a couple of reasons. First, they tend to be hard to put together and break down due to the number of elements required, and they can take up a lot of space if not broken down until the activation zone is reached. For optimal performance, eg ~12dBi forward gain, the antenna needs 10 directors, 1 reflector, and 1 driven element. Smaller, more compact Yagis that consist of just 4 directors are also popular, which still provide ~9dBi of forward gain, 

4-element VHF Yagi (DW1ZWS)

Jerry (K0ES) and Walt (W0CP) working 2 meters with a home brew Yagi
(Activation of W0C/PR-025 (Rogers Peak), in 50 MPH winds)

I've seen home brew Yagis of this type based on a fishing pole with small elements, which work great, except in high wind, they can get really unwieldy. In the photo above, Walt was holding the Yagi while Jerry made contacts, and the elements kept falling out, making it very difficult to manage. 

After doing some research into directional antennas, I came across the Moxon. Invented by Les Moxon (G6XN, SK), Moxons are rectangularly shaped, simple, mechanically robust, single frequency, two-element parasitic arrays. In other words, still basically a Yagi, but in a much simpler form factor. As such, they share many of the same characteristics, namely that they are highly directional, with high forward gain (~10dBi!). And, like a Yagi, it can be used vertically as well as horizontally (for the respective polarization). Based on this, I decided to build my own Moxon.

A handheld 2-meter Moxon, horizontally polarized

In this image, you can see the Moxon that I based my home brew build on (Thingiverse "Thing"). Note that the antenna is directional at the feed point. In other words, in the picture above, note that the feed point is opposite the handle, and the forward gain will be in that direction (away from the handle).

Next, I found a Moxon calculator that only requires two inputs: the desired operating frequency (I used 146 MHz, as the US simplex VHF calling frequency is 146.52 MHz), and the wire gauge to be used for the elements. I initially built a prototype using piece of cardboard and some 14-gauge bare copper wire, along with a BNC connector that allows wires to be easily connected to it. 

2-meter Moxon prototype

After testing the antenna on some local repeaters and with a couple of buddies on Simplex, I was confident the design worked. So I progressed to the next step, which was to acquire the parts and build the connecting pieces on my 3D printer. I acquired a few pieces of 6mm aluminum tubing for the elements from my local home store, along with a few screws, and I was ready to start.

This is the output of the calculator, based on 6mm diameter and 152 MHz:

From there, it was a pretty simple process. I cut four pieces of tubing per the table above, printed the connectors specified in the Thingiverse plan, and found an old yardstick to use as the handle / support. Then I attached the BNC connector to the feedpoint / driven element, via a couple of short pieces of copper wire and clamped together using the 3D printed pieces. Then, it was just a matter of connecting it all together and testing it out. After a few local tests, the antenna was ready for a real field test!

I broke the antenna down into its four pieces, which fit nicely inside of my backpack, and took it along on an activation of W0C/FR-060 (Berrian Mountain), connecting it to my Yaesu FT-70D and pointing it toward Denver. The test was a smashing success--6 VHF QSOs in 11 minutes, and every one came back with a 5/9 signal report! The furthest contact came from a guy using a 5-watt HT at Cherry Creek Reservoir park, using a rubber ducky -- 50+ miles away! In subsequent outings, I was able to make a summit-to-summit contact with a guy up on Pikes Peak, over 100 miles away. 

The final product on its maiden voyage

I am already planning on building a version 2 of the antenna, which will replace the plastic connectors with aluminum connectors that will screw together via threaded "double nut" connections, and a better handle made from some sort of collapsible rod, like a small fishing rod. I'm also thinking about building a 6-meter Moxon to use with my ICOM IC-7300 at home. 

In conclusion, I'm really pleased with the performance and ease of use of the Moxon antennas, and if you're looking for a highly directional 2 meter antenna, definitely consider building one yourself!

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