AA8IA Amateur Radio

Archive for February, 2011

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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The RF Connection

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The RF Connection ( http://www.therfc.com )

One of my hobbies is scanner monitoring. I particularly like to DX the 800 mhz trunked systems in and around Ohio. I try to be efficient in my use of cables / adapters / connectors since every dB counts at 800 Mhz.

For so long I’ve been sick and tired of purchasing subpar connectors and adapters from local places such as Radio Shack and Hosfelt Electronics. I’ve gotten tired of sloppy connectors that either pull apart or simply do not make a tight connection and thus are intermittent.

In comes The RF Connection. I heard about them from Dale Parfitt (PAR Electronics). I figured if they were good enough for a craftsman like Dale, they would definitely be good enough for me. So, last week I gave them a call and told them I’d like an N-Female to BNC-Male adapter, four short jumpers with BNC Males on the end, and two longer cables with BNC Males on the ends.

Well, I just received them all today. As soon as I started unpacking I knew I was in for a treat. The BNC connectors that they used on the end of the jumpers are outstanding. There is no slop whatsoever in them. I plugged them into multiple scanners and attempted to find an intermittent one, but each and every one fastened securely and provided a nice clean connection.

RG-58 was used for the jumpers per my request. Even though they are short jumpers, I tend to abuse them. I wanted rugged jumpers. I’m not concerned about the loss since (a) the jumpers are only 3′ long and (b) they will be used on the outputs of a Stridsberg MCA204M multicoupler, which is an active multicoupler providing a little gain on the output of each port.

The cable<-->connector junctions on these cables are beautiful. I couldn’t have done a better job if I had spent many hours on making them myself. I have no concerns about an end pulling out if a scanner falls off the table and has to dangle by one of these jumpers.

Incidentally, they don’t advertise on their website that they make up custom cables. However, I knew when speaking to Dale Parfitt recently that RFC would indeed make custom cables. So I called them and asked. They said sure and asked me what I needed. I told them about my application and asked them to give me their recommendation. Ultimately they’ll make the cable you want, but it didnt’ hurt for me to hear what they recommended.

The cables aren’t cheap, but rarely does anything of high quality end up being cheap. Great cable assemblies, great adapters, great connectors, and great customer service. If you’re ever in need of RF connectors, adapters, cabling, tools, etc you should really take a look at The RF Connection. I give them 5 stars!

Written by Mike

February 19th, 2011 at 6:52 pm