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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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160 meter antenna for limited space

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When I first got back into the hobby I had no ambition of operating 160m. I had never had a proper antenna for 160m in the past. My experiences revealed that it was very difficult to hear stations on 160m.

Times have changed. I’m interested in a challenge. I’m interested in Contesting. I’m interested in DXing. Furthermore, after doing some reading I realized that there are times when 160m is better (nighttime, winter, solar cycle minimum). It very well could have been that the combination of a lack of proper antenna plus exploring 160m during the summer and/or at the height of the solar cycle caused me to come to the wrong conclusion about 160.

Now that I’ve pretty much decided upon a plan this fall to get my 100+ ft doublet (technically not since its terminated with a balun and 8 ft of RG-213 after the ladderline) up in the air permanently, it’s time to move on to thinking about possibilities for 160m.

I’m ruling out a dipole for 160m for multiple reasons. I lack the space for anything even approaching an efficient 160m dipole. A dipole isn’t the best antenna for DXing 160m, especially if you are unable to get it up in the air above 65 feet. An inverted-L seems to be an extremely popular antenna for 160m, and from the reading I’ve seen it’s doable here. I could potentially get the vertical section of an inverted L up about 45-50 feet. And I would have enough horizontal space to run the horizontal portion of the L out the remaining distance. I’ve read about 1/2w loaded inverted Ls, but the 1/4w inverted L is simple and effective. I’d probably go with what is best documented, and that would be a 1/4w with a good radial system. This antenna would be a wintertime-only antenna. After the mowing season is over I’d throw out as many long radials as I could out from the end of the back yard up into the side yards. I have no experience creating matching systems or anything like that. I don’t have an antenna analyzer, and an analyzer certainly would be a useful tool to have.

160m is a challenge for DXing. But I could potentially create a 160/80m combination inverted L if i were ambitious enough and try my hand at some DX on 80m as well.

I must have bookmarked 30 different websites documenting various inverted-L antennas today. I’ve still got plenty of reading to do. Noise on 160m receive is also often an issue. I venture to say a beverage would not be doable here. I could run a beverage many hundred feet downhill into neighboring land that doesn’t belong to me and nobody would ever know. But I question how useful it would be if it’s laid out in the woods and would be continously decreasing in elevation at the bottom of the gulley. Seems like way too much work. If I can get a 160m inverted-L up for transmit, then I’d probably just use that antenna for receive and see if I enjoy 160m enough to try and improve the receive side of things over the course of the next year.

Yep, I think I’ll put some effort into getting an inverted-L up. Seems like a useful antenna.

Written by Mike

September 1st, 2010 at 6:51 pm

Posted in Antennas

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