Building a Moxon for 40.6 MHz

After looking at various assembly methods for 6m Moxons, I finally settled on a design, scaled it to 8 meters and bought the parts. Total price was right around $28.

 

If you've ever thought about building a Moxon for any band between 2 and 10 meters, I highly recommend taking a look at this video from Steve AD4XT. It provides an effective way of providing a central spreader and a mount, all in one - and at a low price.

Steve's Moxon is for 6 meters. I used this calculator to determine the proper dimensions for an 8m version.

This required that my copper tubing be longer than used in Steve's Moxon since the fiberglass portion is fixed at 48". Longer lengths of these fiberglass stakes are not available so the increased length of the spreaders must come from the copper. I used 24" copper; Steve's are cut to 15" for the 6m Moxon.

I used the same vinyl tubing as Steve to hold the fiberglass rods in the copper and I took the extra step of hammering the copper flat on the ends to more tightly grip the spreaders. I don't intend to use this antenna in other locations so I have no need to ever disassemble it. 

 

The U-bolt assembly was borrowed from another antenna.

After this photo, I hammered a wider flat area to fully accommodate the mounting hardware

 

I secured the wire elements to the spreaders with zip ties knowing that I would have to make adjustments to the wire lengths to fine-tune to my exact frequency of interest. My plan was to then drill a hole in each spreader's far end, once the tuning was completed, and run the wires through them. But the wires are very secure with just the zip ties, so I'll leave it as is for now.

They stayed secure for about a day in our Texas heat. This morning I drilled each spreader about an inch in from the far end and passed the wire through the holes. Much more better now - should have done it that way to begin with.

Once the wire elements are pulled to their proper dimensions and secured, the spreaders bend toward the center, preventing the wires from sagging.

My initial check of SWR was 2.8:1 with a resonant frequency of 38.9 MHz. Plugging this number into the Moxon calculator and comparing it with the dimensions given for the desired frequency allowed me to determine how much wire to trim.

I did this at the sides of the Moxon, pulling the wires through the side insulators 1" at a time, keeping each side symmetrical with the antenna mounted on a 6-ft pole.

 

It is now on my chimney mount with an SWR of 1.2:1 at 40.662 MHz.

I have added an 'Operating on 40 MHz' page to the area just below the banner photo at the top of this page. A small text box has been added to the top of this blog's right-hand column as well.

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