Moxon en GNU/Linux

The Moxon is a simple two-element directional antenna that is compact, lightweight, and easy to build.

It can be manufactured in many ways. There is a dedicated website for these antennas where examples of the most diverse construction methods can be seen.

I have been modeling a Moxon for 6 meters and comparing different dimensional relationships.

From what I have observed, the algorithm developed a few years ago by Cebik is apparently optimal, at least in terms of three important parameters: front-to-back ratio (F/B), feed point impedance, and useful bandwidth (2:1 SWR).

The antenna exhibits moderate gain but the front-to-back ratio is excellent (in models it ranges from 30 to 60 dB) for an antenna of this size with only two elements.

Andy Stewart, KB1OIQ, has developed and published a GNU/Linux version of the popular MoxGen program, which is Free Software (GNU v3 license or higher).

The program makes experimenting with the Moxon extremely easy since, apart from displaying the antenna sketch on screen with dimensions calculated for a frequency and element conductor diameter (which must be uniform throughout the antenna), it produces a PDF plan of the antenna and a .NEC file for working with the model in NEC2 (on GNU/Linux you can use xnec2c, antennavis, qantenna).

In a short time you can test various configurations, stack them, create multiband and bidirectional versions thanks to this application that eliminates the need to perform calculations.

The equations on which MoxGen is based produce a suboptimal result in terms of F/B when using a conductor with a large diameter relative to the antenna’s wavelength (up to a certain point. With really large diameters, this parameter doesn’t deviate too much). In this case, the point of best F/B ratio is slightly higher than the design frequency. This is because Cebik’s original equations are regressive approximations over NEC models.

For example, when designing for a frequency of 51.1 MHz with a conductor diameter of 12.7 mm (1/2"), the point of best F/B ratio is around 51.5 MHz. It should be noted that the model still predicts a respectable F/B ratio > 25dB at the design frequency.

fl_moxgen can be downloaded from here