3BMOX antenna overhaul (2)

 

A while ago I continued the 3BMOX overhaul. As you can see on the photo I mounted everything according the user manual. Some bolts/nuts were missing and had to make new ones. So far it was not too difficult. Resonance on the 20m a bit on the high side, resonable on 15m but very bad on 10m. I really doubted I did mount something wrong. But measured everything and it everything was mounted exactly the way it should.

Here some measurements:

I asked and read about the issue. It is probably a matter of mounting the antenna too close to the ground. So I raised the antenna 1 mtr. Resonance was still on 28.2 MHz but SWR went down to 2,5:1. It could be right? Unfortunatly SWR on 15m went up from perfect to 1,3:1 after I raised the antenna. I wish I could put it up higher but the antenna is too heavy (22 kg) and big to do it on my own.

My opinion about this antenna is that it is build well except the clamps material that isolates the elements from the boom. I'm not shure what material is used but I think it is POM. From what I heard is that white POM is not UV resistant, the black variation is. This material is also called Delrin, although I think that is a brand name. Personally I stick with Stauff clamps (PP material) when building antennas. The 20m moxon itself is a bit flimsy. I really am not shure what windforce this antenna can have... but that would be another story.

The 10m SWR is a bit suspicious. All the antennas I ever build had good SWR also near to the ground, only the resonance would shift after raising the antenna. However, this is a multiband antenna with sleeve fed dipoles on 15m and 10m. It could be working different from what I am used to.