Doing 40 Meters On A Wire

You haven’t fully utilized your ham radio capacity until you’ve tried to construct a dipole.

A simple wire dipole is center-fed as the driven element. The dipole was invented by Heinrich Hertz around 1886.

The dipole is one of the most popular antennas and one of the most practical. It is easy to design and easy to install. In fact, the set of rabbit ears we used for the TV is an example of a dipole antenna.

Any ham radio enthusiast will know that to formulate the magic number for the dipole, one would divide 468 by the frequency. This would give us the full length of the wire. And of course each half or leg, would be half of that number.

For example, say we want to cut a dipole for the 40 meter band, we would want to find a frequency that we often talk on. Let’s use 7.150 MHz. Dividing 468 by 7.15 we get 65.4 feet. We call this a half-wave dipole. Each leg would be 32.7 feet in length, which is called the quarter-wave.

So, I took a piece of insulated copper wire, 12 gauge solid to be specific, measured it and cut it. No big deal at all.

I ordered a center piece to attach both legs to, which is called a center insulator. The center insulator can be purchased at your favorite place that you buy amateur radio gear. My center insulator was around 14 dollars. It had two opposite ends to attach the wire to using bolts.

Simply wrap the wire around the bolt and tighten with a wrench. I used an adjustable wrench and a pair of needle-nose pliers. That’s it. I had some rope on hand.

The store-bought center insulator worked magnificently. This obviously gives you something to attach the wire legs to and allows you to pull tightly on the wire. You want to take the slack out of the wire to get the best height you can muster. I forgot to wrap the wire around the ears of the center insulator before connecting it to the bolts and I quickly found out that was a no-no.

I also purchased what is called dog bones for the ends of the wire. These are small plastic pieces that have holes on each end, for a place to attach the wire and rope. The dog bones or insulators, cost around 50 cents apiece and they work very well.

So the next thing I tried to figure out was which dipole was more suitable, the flat-top dipole or the inverted vee dipole. It required a lot of work but I wanted to know which design I liked the best. I tried both designs and found out that both versions work well. The flat-top is ran straight across, while the inverted vee is an upside down v, naturally.

The flat-top version seemed to be more broad in nature and generally more versatile, but I’ve heard many inverted vees on the air that sounded absolutely fantastic.

Either way will work fine. I personally liked the flat-top version better. Based on the information that I found online, the flat-top offers a little more gain. Probably not much more gain though.

I had originally cut the wire dipole a little long on purpose, so it wasn’t tuning properly on the upper portion of the band. I went back and cut six inches off both ends and it was resonant. Well, it tuned clear across the 40 meter band. I never have to tune on 40 meters, but my HF radio does have an internal tuner if I need it. I use it as little as possible. I think a resonant antenna works the best. That’s just my opinion.

I use no balun or 450 ladder line; just the wire fed with 75-ohm coax. A good match with a low SWR reading. I get a 1:1 SWR reading with this setup. No problems at all.

The 40 meter dipole was and still is a big winner. I ran mine from north to south. The first weekend I worked over 12 stations in Europe on the wire. Boy was I a happy camper. I’ve worked all over the U.S.

Since I ran it north and south, I am just a little weak to the deep south below me, or so it seems. Guess I’ll have to run another wire east and west. However, a dipole will be omnidirectional if hung at low levels.

Would I recommend this to another ham? You betcha. My wire is only about 25 feet off the ground. I get nothing but great audio reports. Personally, I prefer the monoband antenna. The 40 meter dipole is a good antenna and a very practical choice. Good luck on your antenna projects. What kind are you using?

Happy DXing.

Image Credit:

Image: Rob Wiltshire /