Technical Articles

Part 12: 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 today’s post, I’ll be covering items you’ll need to make your own dipole/inverted-V combo antenna and how to determine the necessary length of wire. To read the first 11 entries in this series, just enter “Trippy” in the OnAllBands search box above.

Before you begin, the first thing you need to do is answer the questions that I asked in part 2:

  • Can you put up a dipole/inverted-V combo antenna outside where you live or only inside? For the antenna we’ll be building, let’s assume you have enough space to put one outside on a balcony. But if you’re only able to put up an antenna inside, you can put up a dipole/inverted-V combo using insulated wire.
  • How much room do you have? For this example, I have 24 feet of room on my balcony. I have a hook where I can hang the apex (the center point of the antenna where the balun is) right in the center of the balcony, so I have 12 feet for each leg of the antenna. But remember, it doesn’t matter how much room I have because I’m using coiling, so I can make it as long as I want, even if I cannot string it out all the way.
  • What band, or bands, do you want to work? For this example, I want to work 80, 40, 20, and 10 meters.
  • How much money do you have to spend? Keep in mind that you will need the following items:
  • A precut length of RG-213 coaxial cable with a PL-259 connector on each end. To determine how much coax you will need, locate where the balun or unun will be placed. You will need enough cable to go from your radio to this point.  Order what you need but don’t make it too short because you don’t want it pulling your radio or antenna tuner off your desk or table. I would make the length of coax two feet longer than the measured length.

    For this example, it’s 12 feet from my radio to the balun, so instead of purchasing 12 feet, I’ll be getting a 14-foot precut piece of coax to prevent pulling and coiling of the coax.
  • MFJ-918 balun for your dipole/inverted-V combo
  • Two porcelain insulators (only one for an end-fed antenna)
  • Waterproof cap for the SO-239 connecter on the balun or unun from Diamond Antenna (DMN-31005). When you’re not using the antenna, this allows you to bring the coax back inside when it’s raining or snowing. You’ll want to do it this way; I don’t know about you, but I am terrible at sealing the coax connector from water.
  • Wire cutters
  • If the antenna is going to be outside, you’ll need 12 gauge single-
    strand, bare copper wire. If it’s going to be inside, you’ll need insulated wire.

Determining How Much Wire to Purchase

  1. Do the math. For our example, first find out how long a halfwave dipole/inverted-V combo is on 80 meters. We will use the exact center of the band, 3.750. You always want to use the exact center of whatever band you’re using because it will match better that way. However, if you plan on either just using CW or SSB, you can use the center of the CW band or the center of the phone band.

Take 492 (the halfwave formula number) and divide by 3.750 to get 131.2 (131 feet, 2 inches). But remember when I said that we have to add 3 inches on each end so we have enough wire to wrap around the end insulators? So we need to add 6 inches to get 131 feet, 8 inches—the length for the entire antenna.

Now we need to figure out how long each leg will be. For this example, even though I only have 24 feet of room on my balcony, I’m putting up a 131 foot, 8 inch dipole/inverted-V antenna (thanks to coiling). I divide 131.8 by 2 legs to get 65.9 (65 feet, 9 inches) per leg. I’ll need two pieces of wire (one for each leg). If ordering wire by the foot, you’ll have to cut it to the desired length. For this example, I’m going to get two 66 foot pieces of wire and cut 3 inches off of each leg to get 65 feet, 9 inches.

If you’ve bought all of the above, you’re now ready to make the antenna! In next week’s post, I’ll discuss putting up the balun (or unun) inside or outside, trimming the wire to the exact length, and connecting the legs.

Questions? Comments? Reach me at hebrown3rd@gmail.com.

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