AA8IA Amateur Radio

Archive for the ‘inverted V’ tag

Modeling my 80m wire using EZNEC

leave a comment

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

Tagged with , , , , ,

Ordered some antenna stuff


Sure, I can make a dipole… I know how, and I have. But i’m not in the mood. Plus, Alpha Delta makes some good dipoles.

I ordered an Alpha Delta DX-EE (40 through 10, shortened on 40). I also ordered a Max Gain Systems MK-6-HD

Once I get this put up and test it out, I imagine I’ll buy an Alpha Delta DX-CC (80 through 10, shortened on 80). The goal is to eventually have the DX-CC set up as an inverted-V strung N/S and have the DX-EE strung NW/SE as a flattop dipole.

A flattop would exhibit some additional gain upwards (good for more local) and an inverted-V would be more omnidirectional.

I’m excited because i am pretty sure I’ll have at least one decent dipole up by FD; although I’m really hoping that by then I’ll have both AD dipoles up in the air. I really want the ability to get on 80 during the QSO parties. The DX-CC isn’t a full length dipole on 80. It’s a compromise. But it beats trying to load up this POS G5RV I’ve got.

Should have the antenna and fiberglass mast Tuesday. then I’ll have to figure out the best place to put the mast and get it secured. It’ll need guyed if I push it all the way to 35′ to secure the dipole, likely at the 20-something foot level. I haven’t decided if I’ll find a way to mount it on my back deck (which is about 10 feet off the ground) or if I’ll mount it at ground level. If I mount it at ground level, secured right above 10 feet at the deck, and have the guys in place, it should have no problems withstanding the winds here. If I mount it on the deck, I’ll likely have to guy it in two places to keep it stable enough.

Written by Mike

May 14th, 2010 at 4:56 pm

Antenna for HF – What to do?

leave a comment

I haven’t ruled out a vertical antenna. A vertical is doable. I’d sure make use of it from the standpoint of DX. But, in the meantime I’d really like to put up a dipole that will perform as best as it can possibly perform.

This means I have to get it up in the air and in the clear of as much as possible. That way it has a good pattern and is able to hear something. Keep in mind, I’ve had dipoles up at various times since 1991. But during all of that time, I didn’t care whether it performed as well as it could… as long as I was making contacts. But now i do care.

If you can picture an inverted-V dipole that lost its middle support and fell down exactly 90 degrees from vertical, that is what my current antenna looks like. It’s a horizontal V, with the center supported at 12′, one leg sloping down the end of the yard at a 45 degree angle and anchored near a fencepost and the other leg sloping upwards at a 45 degree angle in the opposing direction anchored about 25 feet up in a tree.

There can be no predictable pattern; there can be no gain; and the performance is mediocre at best.

So, I want to get a dipole up for 40 through 10. I don’t have 35 foot anchor points for two ends of a 40m dipole, so I have to go with an inverted V and a push-up mast.

To add insult to injury, if I expect it to tune up and have any efficience at all it needs to be fed with ladderline. I’ve never tried to run ladderline into the house and find that it’s not going to be easy to do while isolating the ladderline from nearby objects that might affect it. If I feed it with coax, I potentially can get it to tune on more than one band — but that doesn’ tmean it is efficient. I’ve read a lot about dipoles and what happens when it has a significantly high SWR at the antenna feedpoint and you then tune out that high SWR at the end of the feedline. You end up with a situation where most of your signal is lost between your transmitter and the antenna, depending on the band.

Then there is the issue where a 40m dipole on 10m just isnt’ going to have the pattern I would want on 10m.

I’m thinking that if I get a dipole up in the air, I might construct what some call a fan dipole. Now, we won’t debate the name — although I’ll say that technically what I’m referring to likely isn’t a fan dipole. One feedpoint, two or three sets of wires of differing lengths for the separate bands that I want to have available. A 40m dipole should cover 40m and 15m (7 mhz and 21 mhz) with 21mhz being the third harmonic. then add a another site of wires at the same feedpoint for 20m and another set of wires for 10m, with each set of wires spaced far enough apart from each other so that they do not have appreciable effect on one another. I’m thinking this would likely give me a good performing setup for 40m / 20m / 15m / 10m and I could potentially work 17m / 12m somewhat inefficiently.. but maybe not.

Ok I’m just thinking out loud. at any rate, I really want to get a dipole up. I’d get a push-up mast, probably a 35 foot pushup mast. I’d use a 90 degree angle on the V.

The needed minimum height on a 40m inverted V with a 90 degree angle is 21 feet. However, one would want to have it a little higher so that the ends of the V could be a few feet off the ground. A 35 foot push-up mast should do the trick nicely and allow the ends of the dipole to be up off the ground a significant distance and out of the way of humans/animals.

Then another problem arises. if you are using a push-up mast, at least in my area, you must guy it. Guying is a pain in the ass. Suddenly that inconspicuous dipole that you erected isn’t so inconspicuous when you have to have guy wires flailing around all over the place.

I want a dipole, regardless of whether I have a vertical or not. A vertical’s takeoff angle is going to be one that favors DX, and there is a lot of the US that I would like to work as well. Plus, a dipole as a general rule is going to be quieter, since a vertical is more susceptible to manmade noise. It’s only logical for an amateur radio operator to have at least one dipole in his/her arsenal, regardless of whether they have a couple of 100 foot towers with stacked arrays on them covering the bands or a nice vertical.

There are more opinions about the best antennas to have around than there are assholes, and a lot of those opinions come from assholes. But, there also are a lot of knowledgeable people out there who are willing to share their thoughts and offer some assistance. The QRZ forums have a handful of such guys. I’ve been reading a lot written by these guys. This is what is causing me so much delay in getting any antenna at all up.

I want to get some antennas up for HF that in total are cost effective, that aren’t complete eyesores to the neighbors, that will weather the high winds here, and that will fit into the limited space that i have available (65′ x 100′).

Written by Mike

May 13th, 2010 at 3:16 pm

Posted in Antennas

Tagged with ,