Moxon up and running

Since a few weeks the 10m Moxon is up and running. It was quite an easy job assembling and mounting it. I have constructed it in a way that makes it very easy to assemble and disassemble it in case of a severe storm (which happens here frequently). From a mechanical point of view, it’s a relative flexible construction which moves around quite a lot when it’s windy, but this flexibility has a big advantage. Recently we had quite a storm with gusts up to 95km/h (60mph), and the flexibility of the Moxon was the reason it wasn’t blown of the roof. The turning radius is just over 2m (7ft), which is much less than any fullsize Yagi, making it also ideal for limited space situations. Mechanically I’m very happy with the result.

Last few weeks conditions have improved significantly, but busy at work an at home, I did not have very much time to do some extensive testing. But, I have been able to make some nice contacts, and the firsts results are quite impressive. The gain is OK, averaging around 6dB better than my 1/4 wave vertical and the F/B (front/back) ratio is somewhere around 15dB. I am still working on the space between the ends of both elements, tuning between 10cm (4″) and 20cm (8″). Getting the right dimension should increase the F/B ratio to 25dB at least. The impedance is 50 Ohm straight on the radiator, which means a matching device like gamma match is not needed, so no electrical losses there. The bandwidth is quite good, SWR is under 2 from 28.000Mhz to 29.200MHz.

As we are moving to winter here conditions should improve, so I can do some more testing in the next 6-8 months. I will try to set it up against a dipole to see how it performs exactly. Next year I will try to extend the Moxon with another 2 elements to make it a 4 element, adding another 3dB extra gain.

I am quite sure now that the Moxon is probably one the most ideal directional antennas.

Moxon spreader mounting in detail

A detailed view on the spreader mounting to the rotor mast. All done with commercially available materials.

Moxon choke balun detail

With 5 turns of RG-58 A/U coaxial cable in a 10cm (4″) diameter, this choke balun “chokes” currents running on the coax’ outer shield, preventing nasty interference on electrical home devices. The end of the coax is connected directly to the radiator.

The 10m wire Moxon

Standing almost 13m (43ft) above the ground, the 2 element Moxon is still a quite low profile antenna.

73 de PA9X Jean-Paul Suijs