A friend told me about some dipoles made from headphone cases from DollarTree. If you aren’t familiar with DollarTree it’s a dollar store where everything is $1. So I went over to my local DollarTree and bought a few of these headphones that come with a plastic case.
I opened the package and removed the headphones and the extra rubber plugs from the headphone case. Threw the headphones in a drawer. I can use them later. There are some little tabs in that held the headphones in place in the center.
I clipped the two tabs and the flat piece sticking up in the center of each headphone case.
I left the other four tab that were not in the center there. They will be used later as extra strain reliefs for our wires. After clipping two headphone cases, I put them with the slit faces opposite directions and glued them together.
After my first attempt with one with the wire I had laying around the shop I decided to make one with some smaller gauge wire. I didn’t have any smaller gauge wire, but I did have some Cat 5e ethernet cabling. If you are unaware Cat 5e ethernet cabling has 4 twisted pairs of 24 gauge wire. 24 Gauge should fit nicely and since this antenna is designed for QRP (low power), and should work fine.
There is one problem. We need some pretty long wires and trying to untwist the pairs by hand to get the individual strands could prove difficult. I cut some Cat 5e cable a bit longer than I would need and separated the four pairs. I then placed one end of a pair in my vice. There was enough room to do this in my shop because it’s pretty big. If you don’t have room inside you could tie the pair to something outside and do this. I put the other end of the pair in my drill.
I stretched the wire out so that there was tension across the whole piece of wire. Then I ran the drill until the pair was completely untwisted keeping tension on it the whole time. If you don’t keep tension you’ll start twisting the part closest to you the opposite direction while the rest of it remains untwisted.
After untwisting the wire measure and cut to length for the size you need. The formula for a dipole is 468/Freq in MHz. Each leg will be half that length which is 234. An easy way to memorize this is for every “1” leg it will be 234. So memorize 1234. You can also use the dipole calculator on this site to help you out building and then tuning your dipole. Using the calculator for a 40m dipole we need to measure out two legs that are 32′ 7 3⁄8” long.
Measure out the wire, and then it is a simple matter of sliding the wire through our strain relief holes and soldering it to our connector. The first one I made I used a SO-239 connector. On this second one I used a BNC connector. The BNC connector is a good connector, weighs less, and takes up less space. Many QRP radios come with BNC connectors also instead of the ubiquitous SO-239.
Solder one leg to the center pin and other to the ground lug. Once the legs of the dipole are soldered up to the BNC connector we can wrap the wires around each of the headphone cases.
As you can see in the picture above above the wire for a 40m dipole fits on here just fine with plenty of room to spare.