Thursday, July 7, 2016

End Fed Matchbox Antenna

I got my start on HF by using a 40 meter double bazooka I made from scrap 75 ohm coax I had laying around. It worked very well, though unfortunately some tree trimmers tore it down. On a positive note, I got to experiment with a new antenna design.

The End Fed is an antenna that is very simple in design and you can install it in a variety of configurations. In it's simplest form you can use a random length piece of wire, at least 1/4 wavelength of your operating frequency, and throw it up into a tree. Regardless of how you string it up, you are going to need a matchbox or UnUn.

I pulled most of my information from the following PDF. ( They have the best assembly instructions I could find. I would advise reviewing it if you cannot follow mine as they have better pictures.

Most of the designs I looked at used a 9:1 UnUn inside the matchbox. The toroid type varied. Some were huge and others were pretty small. I found that the T130-2 toroid seemed to be popular among other hams that were building this antenna. Supposedly this one will handle around 300 watts, so if you want to run high power, you may want to look for a T200-2.

T130-2 Toroid Core
Having never wound a toroid core before, I found it a little tricky. I used 20 inch pieces of 20 gauge wire to wind the 9 turns on the core. I made two of these cores so I could experiment with a couple different designs. On one I used a piece of power cord from a broken printer. It was three, 20 gauge stranded wires that were held in place by flat insulation. This was easier to wind since the wires couldn't get twisted out of order. On the other core, I had to use some single silver plated 20 gauge wire and try to keep everything in order. After getting the wire wrapped around the core nine times, I used electrical tape to hold all the wires in place.

The core winding is really the hardest part. After that you have to find an enclosure, connectors, and get everything soldered together. I went to the hardware store and found a marine junction box and some bolts, washers and wingnuts.

All the directions I found for making this core online were using nice color coded wire. I didn't have any laying around, so I had to be extra careful to keep track of the order the wires were in. But the principal is the same. If you are looking at the front of the core and are using colored wire, you should have a green, black, and red wire to the left side as well as the right side. Both in the same order.
Marine Junction Box with UnUn installed
You need to solder together the left black wire to the right red wire. Twist the left green wire to the right black wire for about two inches. Then strip the remaining right green wire about two inches from the toroid.

I used crimp-on terminal lugs for the ground and aerial connections. You can go ahead and crimp and solder a lug on the right red wire for the aerial. Then add a short wire to the right green wire, crimp and solder both into a lug. This will be connected to the ground/counterpoise.

The twisted green and black wire will need to be skinned and soldered to the center connection on your SO-239 connector. Finally the right green wire lug is attached to the counterpoise and the loose wire is soldered to the ground of the SO-239.

Matchbox with 72ft of wire
Once the matchbox is assembled, I had to decide what length of wire to use. Depending on who you talk to, you either want a perfect half or 1/4 wave to be resonant on the band you want to operate or you want a length that is not resonant on any band so you can use a tuner and work many bands. The instructions linked above say to use a 26 foot wire to achieve 40-6 meter performance. I wanted to tune easily on 80-10, so I chose to use a 72 ft. wire.

To mount the antenna, I climbed up on the roof and screwed the box directly to the wall in the highest eve on the house. I then twisted the end of the wire around the nut on top of the box and tightened the wing nut. Luckily I have a barn just the right distance away from the house. I was able to attach it to the wall of the loft. I used a UV resistant wire tie that accepts a screw to mount it to the wall. I then ran the wire through the loop created by the wire tie and twisted it back around on itself several times. I also used a length of 12 gauge wire to run from the counterpoise lug, down the wall to a ground rod driven into the ground below the antenna.

The antenna wire is pulled straight and doesn't look like it sags at all. It's at a height of about 26 ft above the ground. I wish I could have gotten it higher, but it seems to work well. I can tune it easily from 80 through 10 meters and have made several contacts on each band during my testing. I wanted 80 meters so I could connect to Winmor stations here in VA and the surrounding area at night. So far I've been able to hit one of the two in VA every night to send and receive my messages.

PVC Matchbox - Portable 
I was also wanting to make an antenna for portable operation or to use as a quick deploy-able backup. So, I put together the same UnUn inside a different case. This time I used a 2 inch PVC cap and plug. I also decided to use 3/8-24 bolts because, by putting a coupling nut on top of the cap, you can attach a standard whip antenna and have a nice vertical. I filled the inside with a little spray foam insulation and glued the cap and plug together so that it would be weather resistant. I'm going to expand on this a little later by painting the whole thing with Plasti Dip. I will say that I wish the bolt for the counterpoise connection was longer. I didn't think about the plug being thicker than the top of the cap. But, I can still make it work.

I tested this design by clamping the matchbox to the front porch railing and pulling the wire into a tree in the yard in an inverted L setup. I also used a piece of wire that was about 18 ft. long attached to the counterpoise lug and laid on the ground beneath the radiating wire. This performed nearly the same as the more permanent installation between the house and barn. (Note: I have read that if you are using at least 25 ft. of coax to feed this type of matchbox, you don't necessarily need a counterpoise wire since the coax shield will act as the counterpoise. I have tested this and it works, however you need to make sure your station is setup farther than 25 ft. away from the matchbox or you will have some RFI issues.)

Bottom showing Counterpoise Lug and SO-239

Top showing Aerial Lug

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