No-Solder, Easy Speaker Wire Dipole!

Hi everyone!

I recently built an MFJ Cub for 20 meters, and boy it is a sweet little radio! I can get almost 1000 miles out on only 1 watt. I only have one problem, though - I don't have a portable antenna for it. I plan on going portable as the weather gets warmer, and I don't want to haul around my base antenna!

Don't worry, though. I have just the solution! Today, we're going to make a dipole antenna that requires NO SOLDERING! Yep, you heard me, no soldering required. Period.

This antenna is a classic design based on the traditional dipole antenna and was featured in QST magazines and the ARRL antenna book. It is referred to as the "zip wire" antenna. This is a compromise antenna, but hey, pretty much every antenna is a compromise, right???

With that out of the way, let's get started!

1. The first thing you'll need is some zip wire. This can be speaker wire or any other moderately thin, insulated wire. 16 or 18-gauge will suffice, but you can use what you have on hand. Try to get a large amount - 100 feet is plenty for most bands
2. The next thing you'll need is a "balun adapter." These typically have any connector on one end with screw terminals on the other. These can be found on Amazon for relatively cheap. Personally, I prefer a BNC connector

And that's it! You'll also probably want a calculator for the next step. If you don't have one already, an antenna analyzer is also great to have. If you're on a tight budget and don't want to invest in higher-end models like RigExpert, the NanoVNA works just fine.

Now it's time for everybody's favorite subject - math!

We'll need to use two formulas, one for the main element and one for the feedline. I will outline that below.

For the MAIN element:

In this equation, we'll use the 1/4-wave formula since you're cutting two elements at the same time. For this formula, we'll take 234 divided by the frequency in megahertz.

234/f

For me, it will be 234/14.06, which results in ~16.643 ft. Just round this up to 17 feet since you'll need to trim the antenna to resonance later on. At this point, you shouldn't have cut anything yet. Just tie a knot near the 17-foot mark on your wire spool.

For the FEEDLINE:

This equation is much different since we'll be including a velocity factor. A velocity factor is a ratio used in comparison with the speed of light. For this antenna design, 70% or 0.7 works just fine. This just means that the signal travels at 70% of the speed of light. Each and every website I've been on states that this is the best value for this style of antenna. The velocity factor is the reason that there is a delay in RF signals because if coax had a 100% velocity factor, you'd hear the signals as soon as the transmitter is keyed or mic'd.

The feedline will also be made out of speaker wire, and because of that, we'll need to cut the feedline to near resonance. In order to do this, we'll use the following formula:

(492/f) * Vf

F is our frequency in megahertz and Vf is our velocity factor. For my antenna, it will be (492/14.06) * 0.7. This equates to around 24.5 feet. Again, this doesn't have to be spot on, just round accordingly.

If we take our element length and our feedline length (17 + 24.5), we get a value of 41.5 feet. This is the total amount of wire needed to make our antenna.

Take your 17-foot section and split apart the conductors. You should now have two elements or legs, which should measure ~34 feet. After you split these, untie your basic knot BUT DON'T SPLIT ANY FURTHER! You'll now need to tie an electrician's knot. An image of that is shown. Make sure you pull the knot tight, as you don't want your antenna to unravel during use!

You're now ready to finalize your antenna! Take your screw connector and attach it to the end of the feed line. Strip some wire off and connect your antenna to the screw side terminal.

Before you can use this antenna on the air, I'd strongly request that you analyze it first. Remember to trim the antenna in SMALL increments. It's better to make several tiny adjustments than to destroy your antenna completely.

When you're done, attach and secure some insulators to the ends of the legs. Support isn't necessarily needed for the middle since the knot holds most of the tension, but you can if you need it. This antenna works best for temporary operations, as keeping it suspended for an extended period of time (over months and years) will stretch it out significantly.

This antenna is the perfect antenna for your SOTA/POTA bag, QRP go kit, or portable operation. If using higher power like 100W, make sure to get thicker gauge wire. Also, keep the feedline away from anything metal - this is not a shielded conductor despite having plastic jacketing on the outside.

I highly suggest using a tuner with this setup. Although it is in theory a resonant antenna, having a tuner will ensure that you aren't unintentionally loading high SWR ratings and possibly blowing the finals. Even if you're using QRP, finals can still be fried!

Sometimes, the feedline may not be long enough for your liking. If you need to add more, add in increments of the feed line's length. For example, if I wanted to add more, I'd add in lengths of 24.5 feet. This will decrease the amount of loss while keeping the antenna and feedline resonant.

Well, what are you waiting for now? Get out on the air and get some QSOs made!!!

EDIT Feb. 3, 2023 - THIS IS STILL A WIP! I WILL POST PHOTOS LATER