Compact 3-Band Moxon-Yagi Beam

Visit OptiBeam OB6-3M is a German-breed high-quality compact 3-band directive antenna exhibiting mechanical and electrical characteristics that are far superior to the already excellent Force12 C3. Hardware is aluminium, stainless steel and UV-resistant plastic. All elements are trapless —i.e. almost lossless. The antenna is fed at a single coaxial feedpoint from where a parallel matched feedline made out of aluminium tubing further connects to the three driven elements. Element spacing and element length is clearly marked, so no tuning is necessary after assembly.

I only added a couple of isolated guying ropes from the mast to the 20m elements, thereby reducing the sag of these elements. I did so in order to prevent the 20m elements from colliding with the rather tall chimneys in the proximity of the antenna.

The antenna configuration is a driver-director Yagi on 10m, a driver-reflector Yagi on 15m and a Moxon beam on 20m. A Moxon beam is a driver-reflector Yagi with the ends of the elements bent towards each other at about 70% of the element length. Due to an augmented coupling between the driver and the refrlector, a Moxon beam typically yields a much higher front-to-back ratio than an ordinary 2-element Yagi beam and this in a more compact design. This type of antenna was first described by Les Moxon, G6XN, in his book HF Antennas for All Locations, RSGB, 2nd Edition, 1993.

The idea of combining a 20m Moxon beam with two 2-element Yagi antennas for the higher bands originated from antenna-guru L. B. Cebik, W4RNL. It was Cebik who made this suggestion to Thomas Schmenger, DF2BO, owner of OptiBeam. Cebik also published modelling results of this antenna configuration on his website. For complete antenna characteristics of the OB6-3M and ordering details visit OptiBeam.

Being an antenna engineer myself, I long pondered about building one of Cebik's antennas myself. I simply could not find any commercial antenna that pleased me with its dimensions, electrical characteristics and mechanical construction. But when I saw the OB6-3M OptiBeam, I decided I prefered to spend my time on other things rather than searching for the right mechanical components and putting together a whole HF beam myself!