Thursday, October 24, 2013

My Multiband Wire Vertical Antenna

When I first got onto HF, I determined my best course was to put a dipole in my attic and build my shack in my bedroom as I live in an antenna restricted community. I put up a 20 meter dipole and was able to get decent results, but I wasn't really able to work much DX on it. After a year or so of that, I decided there had to be a better way.

I started searching online for unique solutions and eventually came across an article from an old QST where a ham in a similar situation resolved to set up a wire vertical in the trees. In the article the ham ran three wires up a tree; he had one cut for 40 meters, 20 meters, and 10 meters. He then laid down a few radials cut for each band. I started by taking an electrical wall box cover and drilling a bunch of holes in it. I then used an acetylene torch to solder the radials and a jumper to another little box I constructed. The box was tiny plastic container I sunk a SO-239 into and soldered the elements and jumper to the radial plate to it. I used silicone to seal the box the best I could. 

This shows the box that connects the SO-239 to the radial
plate and the radial plate itself.
For the radiating elements I used wire staples to attach them to the tree every couple feet. For the 40 meter element I had to affix the wire over to another tree nearby as I couldn't go any higher. This resulted in the 40 meter element being in more of an L configuration. The other two elements are more or less completely vertical up the tree.


Since I used brown wire, you can barely see the radiating
 elements on the tree.
Step away a few feet and my antenna is basically invisible!

Once the elements were up, I began laying the radials out. Since the tree was on a giant garden mount, I ran as many radials as I could around the mound as I was planning to cover them with mulch after I was done. I then ran a few of the longer 40 meter radials out into my lawn, using lawn staples every few feet. This kept them low to the ground and in fact, only a few months later, the radials have completely disappeared underneath the grass. The mound was about eight feet from another mound which led to where the coax enters the house, so I used a spade and dug a trench to lay my coax in. I used direct-bury coax and this particular part of my yard is fairly low traffic, so I think it should survive in the ground without too much issue. I then ran the rest of the coax to the basement window which sits above my operating position.

Luckily, I was able to run a bunch of the radials within
the mound as it save me dealing with radials in the lawn.

To get into the house, I took an extra screen we had for the basement window and covered it with plexiglass. I then drilled a hole and used an outdoor electrical box as an entrance point. I sealed the hole around the cable with Coax-Seal  to ensure no weather or bugs get into the house. I pounded in a ground rod and ran around 100 feet of bare copper wire to bond it to my house's main ground rod, as per the NEC. I put a lightning arrestor inline before any coax entered the house.

This entrance-point setup allows me to quickly add
or remove coax as needed and is fairly weatherproof.

On the inside of the house, the window opens downwards. This allows me to coil up the coax when not in use, tape it to the window, and shut the window entirely so it is as if I never made any modifications at all. This also encourages me to disconnect my radio when not in use as plexiglass alone is not a great heat insulator.

Here is my operating position with my work bench to the left.
You can see how the coax simply drops down to my radio.

As for on-air performance, I am very pleased. Not only does the antenna tune up on 40-6 meters (excluding 30 meters) with my autotuner in the FT-450D, it does better than expected on 40, 20, 15, and 10. I only put down 15 or 16 radials which is definitely on the light side. Still, the first day it was on the air I worked my first European DX on voice in Croatia! I've worked plenty of DX since and I'm loving it! Finally, I'd like to thank my brother, Andy, KK4LWR, for helping me with a bunch of the grunt work of tacking up the antenna and laying out all the radials. This antenna has really allowed me to take my hobby to a whole new level. It's a shame it will only see use when I'm on breaks from college!


2 comments:

  1. How is the noise level? Right now I am using a dipole in the attic and the noise is always S5 or greater.

    Nice blog!

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    Replies
    1. Thanks for the comment! Be sure to check out my YouTube channel via the link above...I've posted much more content there.

      As far as the antenna, noise hasn't been a huge issue. I used to have a dipole in the attic and the vertical is much better. While I couldn't give you figures in terms of noise, I am hearing many more stations and moving the antenna outside prevents any interference in my house.

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