I don’t even have an HF capable radio yet. I’ve spent the month deciding on one and it looks like I’m gonna go with the Radioddity QR20. I’ll write another post about it, once I get it up and working, but I thought, what good will a HF radio do me, if I do not have a suitable antenna. After joining a few antenna maker groups on Facebook, and seeing countless devices that look like the flux capacitor, I decided to build an End Fed Half Wave (EFHW) antenna for attic deployment as well as field deployment. I went with the antenna for a couple of reasons. The first reason… the 49:1 unun transformer looks REALLY COOL. Seriously, I saw it and said “I have to build one”. The second reason, I live in a Home Owners Association neighborhood, and I am not allowed to have an antenna outside. This one will go in my attic. I have plenty of space up there and although its not ideal, you have to do what you have to do. The third reason, you can sometimes get by with not having an antenna tuner with an EFHW. I’ve been told that it certainly wont hurt to have one, but if you don’t have one, you can usually make it work. The fourth and final reason… The ARRL.org EFHW kit I bought, claims it works on 10m, 15m, 20m, and 40m. Though I suspect it works better on some bands than others, this appealed to me since I have limited space and really just want to get on the air.
The kit comes with everything you need to build the antenna. A ferrite toroid (the black donut looking thing), enamel coated magnet wire, a capacitor, the box, all the hardware, ,and of course the 66 foot wire used for the aerial.
The first step is to drill out the holes for the hardware. This part would have been easy had I noticed that the box is not perfectly square. I goofed up and drilled out the hole for the SO-239 coax connector on the wrong side (I’ll have to fill that in with epoxy or something).
Once you’re all drilled up, its time to wind the 49:1 UnUn. This part is important. I followed along on a video, but did not get the winding correct the first time. Before I soldered anything togher, I posted a photo of my work on my Facebook antenna maker group. The problem with my first winding was that I had only 13 turns, when I should have had 14. I then had to undwind the whole thing and rewind. Having this image of the pattern made it much easier.
Once you get that part right, its time to solder the thing together. I’ll readily admit, I’m terrible at soldering, but somehow I managed to solder the 4 or 5 connections. After checking it for continuity with a multimeter, I was assured that I had done it correctly. Slap the cover on it and write your callsign on the sticker and you’re done.
As stated at the beginning of the post, I do not yet have an HF radio. But when it comes in, I intend to be ready. My next step is to mount it in the attic so that it is stable, but also easily taken down so I can take it with me for field work. Then I am going to use a NanoVNA to analyze the SWR on the different bands. I’m told that when using for attic deployment, you have a 50% chance of getting lucky and being able to use it right off the bat without an antenna tuner. If not, you may have trim it and maybe even add a counterpoise. The problem with attic deployment is that any other metal wires or pipes tend to become part of the antenna.
I have also been told that the coax can act as the counterpoise. In my case, I will probably have to use a 100ft run of RG8x and that the length could be problematic. If it does cause a problem, my next step will be to add a ferrite choke on the coax, and add an auxiliary counterpoise, which there is a connecter for on this kit.
I will update this post when I get it all working.
-73 KI5WKB