Antenna Tech / Technical Articles

Part 5: How to Build Antennas from a Blind Ham’s Perspective…and if You’re Not Blind, You’ll Learn Something, Too!

Editor’s Note: Over the next several months, OnAllBands will be featuring a series of articles from Harry “Trippy” Brown, AC8S, longtime amateur operator and antenna builder/tester who’s never let his visual impairment stop him from enjoying the hobby he loves. As the title of this series states, we hope these articles provide you with invaluable insights as you pursue your own successful antenna projects.

In my post last week, I answered a few questions about building dipole/inverted-V combo and end-fed antennas. Today, I’ll be addressing measuring these antennas, how to avoid soldering, the best material for hanging them, and what type/gauge of wire to use.

How do I measure my dipole/inverted-V combo or my end-fed?

For the dipole inverted-V combo, measure the entire antenna from end to end. Then, if using porcelain insulators, add three inches at each end of the leg of the dipole/inverted-V combo (not at the balun end, but at the end where you tie each leg off at the insulator). Divide the total number for the length of the antenna by two—that number will tell you the length of each leg of the antenna.

For end-feds, add three inches at the end where you connect the wire leg to the insulator. Then measure the entire antenna, including the coax length and the length of wire for your antenna leg. The whole antenna (including the coax and wire leg) must equal at least a half wave. Note: I use only porcelain insulators because it’s a lot easier to wrap the wire around them. Also, porcelain insulators are immune to the weather, unlike those that are made of plastic and aluminum.

Measuring a Half Wave Dipole/Inverted-V Combo for Use on 75 Meters Example: At 3.750 KHz, take the number 492—the new number for a half wave dipole/inverted-V combo (not 468 anymore)—and divide that by 3.750 to get 131.2, meaning 131 feet, 2 inches. Then add 3 inches on each end for the tie-off insulator so the total length is 131 feet, 8 inches. Divide 131.8 by 2 to get 65.9 (65 feet, 9 inches per leg).

Measuring a Half Wave End-Fed Example: Again, it’s going to be built at 3.750 KHz. It’s also 131 feet, 5 inches, but for an end-fed, we’re not as picky about coax length for the leg. So, let’s say we’re using 100 feet of coax. The wire leg will be 31.5 feet, which includes 31.2 feet plus 3 inches for wrapping the wire around the insulator at the end. This gets us to 131 feet, 5 inches.

What about connecting each leg of the dipole/inverted-V combo to the balun, or the piece of wire to a 56 to 1 unun for the end-fed? Can I do this without soldering?

Soldering doesn’t work for me. If you’re using single-strand bare copper wire, which is what I use, you don’t have to solder each of the legs of a dipole/inverted-V combo if connecting each leg to a balun that is equipped with I-hooks (same is true when connecting an end-fed’s wire to an unun that has I-hooks).

Here’s another reason not to solder from an article by NJ2L: “An antenna that depends solely on solder joints to handle wind stresses will surely fall down sooner than one that’s made with good mechanical connections.”

Instead of soldering, just use single-strand bare copper wire and hook each leg of the dipole/inverted-V combo onto each I-hook on the balun or hook the piece of wire to the unun for an end-fed. Make sure it’s twisted really well so it cannot come disconnected. To make sure it’s still connected, I always go outside and check each leg of the dipole/inverted-V combo before turning on the radio.

I live in a part of Michigan that gets high winds quite frequently, 70 MPH or higher, and I’ve never had had a dipole/inverted-V combo come down or come unhooked.

Is there a best way to keep my dipole/inverted-V combo or end-fed up so the winds cannot blow it down? What kind of rope should I use for hanging them?

When putting up a dipole/inverted-V combo or end-fed, make sure the materials and the supports are strong enough to withstand heavy winds without breaking. You can use rope, but instead of rope on each
end and in the center, I use copper wire. I don’t use rope because rope can wear out in the weather, unlike copper wire. Instead of putting a piece of rope through the opposite side of the end insulator from each copper leg of the dipole/inverted-V combo, or through the opposite side of the end insulator from the leg of the end-fed, I just put a piece of copper wire through it and wrap it like a piece of rope to each end support. I also use a piece of copper wire for the top hook in the center of the balun, or the unun, where the piece of rope would go as well. But you can use rope if you prefer.

What kind of wire should I use to build my dipole/inverted-V combo or end-fed?

If you’re building a dipole/inverted-V combo or end-fed for outside use, use 12 gauge single-strand bare copper wire. It’s the best for reception and transmitting. If 12 gauge isn’t available, I use 14 gauge. As antenna guru W4RNL recommends, “Thicker conductors have a wider operating bandwidth over which they attain a practical standing wave ratio.”

Since thinner wire is not as broad-banded, that means you’ll be retuning your dipole/inverted-V combo or end-fed more often. The less time you spend retuning, the more time you’ll be spending talking to people on the radio. I might even look at 10 gauge copper wire and see if I can cut it with wire cutters and get it through the I-hooks. If you’re putting it up indoors, use insulated wire (hams have used insulated wire indoors with great results running 20 watts or less). Note: When using an indoor antenna, your power should be no higher than 20 watts. Also be aware that insulated wire does not receive or transmit as well as copper wire or coax.

Next week I’ll be discussing the use of insulators, the need for antenna tuners, and more about measuring.

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