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Modeling my 80m wire using EZNEC

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I’ve played around with EZNEC briefly before, but not enough to have really learned anything useful. But, yesterday I decided I’d install it again and attempt to do some really basic modelling of my current primary antenna.

A few things of note:

  1. Primary antenna is a 105′ long inverted V with the apex at 37′ and the ends at 0′. Yes, you read that correctly — ends at 0′. There is an approximately 39′ section of 450-ohm ladderline feeding this, which then runs into a DX Engineering 4:1 current balun and then into my LDG AT100Pro tuner. The center support is at ground level of the basement of our ranch home. The antenna wires are parallel with the back of the house and are approximately 13′ from the back of the house. The length of this wire is oriented nearly N-S (about 10-12 degrees W of N. Broadside would be nearly E-W (about 10-12 degrees S of W
  2. Secondary antenna is an Alpha Delta DX-EE, which is a shortened [using a coil] 40m dipole with separate parallel dipoles for 15 and 10m. This is about 11′ off the ground on one end and 35′ off the ground at the other end, with a slight droop in the middle due to having no center support and the weight of the LMR400 that is attached to it. This ends of this dipole are oriented NW-SE. Broadside to this antenna would be SW-NE.

My first antenna was the DX-EE. It worked well enough for being so low, but only on 20m through 10m. It would tune on 80m but lacked any efficiency. It tuned fine on 40m, but it’s shortened and really didn’t perform like I wanted it to. Because I primarily like domestic contests, I wanted/needed to have 40m/80m performance. That is why I decided to put up the Vee.

Obviously these are both compromise antennas because they are shortened antennas for the lowest bands I want to use them on. Besides, they are way to low to the ground.

At any rate, when I got the 80m wire up I was pleasantly surprised at the performance. I was having great fun in the domestic contests and considered this antenna to be a great success. I was hearing and working stations very well that I couldn’t even hear on the DX-EE. Life was good.

I then participated in the ARRL International DX contest this year (CW) and realized how poor even this antenna is for non-domestic contests. So far I haven’t found a way to really improve upon that as far as antenna design / height goes. But I decided to do some modeling in EZNEC of the basic 80m Vee itself, as it is erected in my yard.

What I saw in EZNEC shed some serious light on things.

3.525 Mhz 3D plot with ends at 0′. Mostly omnidirectional with some favorability in the direction parallel to the dipole.

3.525 Mhz 2D plot with the ends at 0′. Max gain -0.5 dbi (-2.65 dbd).

3.525 Mhz 3D plot with the ends at 8′. Omnidirectional.

3.525 Mhz 2D plot with the ends at 8′. Max gain 5.07 dbi (2.92 dbd).

Lifting the ends off of the ground 8′ results in not only a more omnidirectional pattern but a remarkable improvement in maximum gain to 5.07 dbi (2.92 dbd).

Certainly this reveals that what the experts tell you is true — GET THOSE ENDS OFF OF THE GROUND! In my case, it looks like I would gain 5.5 db by simply elevating the ends of the dipole. This has to be the cheapest and easiest 5 db that I’d ever gain.

Similar remarkable results can be seen on the 40m (7.025 Mhz) plots for this same antenna, visible below.

7.025 Mhz 3D plot with ends at 0′. Pattern fairly omnidirectional but favors 45 degrees broadside to the wire.

7.025 Mhz 2D plot with ends at 0′. Max gain -0.11 dbi (-2.26 dbd).

7.025 Mhz 3D plot with ends at 8′. Omnidirectional pattern.

7.025 Mhz 2D plot with ends at 8′. Max gain 5.97 dbi (3.82 dbd).

NAQP RTTY contest is this weekend. I’m hoping to get the ends elevated up off the ground before the end of the day today.

Written by Mike

February 25th, 2011 at 11:57 am

Posted in Antennas,Posts

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