Home > HF, Home Brew > NEC Modeling of the 20m Vertical Moxon

NEC Modeling of the 20m Vertical Moxon

You may remember me writing here about constructing a 20m vertical Moxon antenna for use in the Oceania DX contest.

The attraction of the vertical Moxon was the simple construction and the advantage of being able to hang it from a high tree branch.  Additionally it was claimed by other constructors, that it gave a low take-off angle even when mounted close to the ground.

As I wrote in my previous post, I found the DX performance excellent and local performance not so good, indicating that it did indeed have a low radiation angle.  Of course real world testing is always better than modeling, but I decided to model the antenna in Cocoa NEC to see if raising it higher (something I cant do at present) would result in better performance. I found that a change of height from 2m above ground to 12 meters above ground reduced the central lobe concentrating more energy at lower angles but that  the difference was not huge. In other words the vertical Moxon for 20m works almost as well at 2 metres elevation, as it does at 12m elevation.

Here is the geometry

 

Geometry of the vertical Moxon antenna

 

 

Azimuth plot- The antenna is slightly directional

 

 

Best gain 5.6 dB at 31 degrees

 

Now the plots at 12 meters elevation

 

Azimuth. Slightly better gain (10dB)

 

 

Elevation Plot

 

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Categories: HF, Home Brew
  1. Marc
    December 24, 2012 at 4:23 pm

    thanks for this moedlisation but the front to back ratio doesn’t seem to be present ???

    • olsenstours
      December 24, 2012 at 7:32 pm

      Hi Marc

      Yes it is. 9.76 dB. See Directivity in second image.

  2. Marc
    January 2, 2013 at 9:03 pm

    Hi David,
    According to you the F/B ratio is around 10 db only … As i’m not able to put up any tall tower with yagis i’m going to make one vertical moxon in order to see how this antenna really works lol

    Thank you my friend and happy new year !!!!!!!!!!!!!!!!!!!!

    Marc

    • olsenstours
      April 16, 2013 at 10:55 pm

      I hope it works well for you, watch out for interaction with the metal tower, note no metal in my support structure.

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