EFHWA Revisited

KC2UHB with EFHW Tuner

Our favorite fashion hacker/ham, Diana Eng, KC2UHB, has posted a new article on the Make Magazine blog with instructions on how to build an End-Fed Half Wave antenna tuner and deploy it with an antenna. (BTW, did you see that she was recently named to the ARRL Public Relations Committee? An excellent choice the League.)

Her BOM calls out an air variable cap from MFJ and a T94-2 'roid, so I suspect that her tuner could handle a bit more than QRP power. In typical ham fashion, it appears that she was too eager to get it on the air to worry about little things like putting it in an enclosure. FB with that Diana, I think most of us can relate.

It sounds like she had great success using this setup with her FT-817 for some SSB QRP fun:

Setting up my antenna for 20m the first time took about half an hour, and I was able to get very close to 1:1 SWR using the 9:1 input with a vertical wire supported by a tree. Over the next hour or so, operating from a park bench in Brooklyn, using 5 watts on sideband, I made contact with stations in the US, Europe, South America, the Caribbean, and Hawaii. The furthest station was about 5000 miles away, which means I was getting 1000 miles per watt out of this setup. I'm sure it was a big contest station and not another QRP operator sitting on a park bench with a wire antenna, but it was still fun.

I'll take this opportunity to shamelessly promote my own EFHW tuner, which I've managed to get back up on my new website. Don't forget to compare to AA5TB's design, which features probably the best page on this subject matter which I've seen.

5 thoughts on “EFHWA Revisited”

  1. Great stuff - thanks for posting Jason. When portable, I've used a Buddipole and Buddistick, wire dipoles, and an endfed 85 foot wire with a 17 foot counterpoise (the W3EDP antenna), but I've had it in my mind to try the EFHW for a while now. I think this will be my next portable antenna. Polyvaricons and toroids here we come!

  2. I think you'll be pleasantly surprised by how well the EFHW works. If you deploy it vertically, you of course get a nice, low takeoff angle. I haven't had a chance to try one since ol' Sol started making his comeback, but I bet it will be great for the upper HF bands now that propagation is picking up a bit.

  3. The EFHW is my absolute favorite skyhook. It's simple to put up, simple to tune, just feels intuitive. I built the matching unit and had my QRP rig and an SWR bridge out one day; as I turned the air cap I hit this sweet spot and the SWR fell to 1:1 and the stations just poured in loudly all at once; I was just so thrilled and gratified I've been hooked on this antenna since then. In fact, I'm actually looking for the plans to build one for my QRO rig right now.

    73,

    Les
    KE7SLX

  4. Les,

    The difficulty that you'll run into when operating QRO is the very large voltage developed on the end of the antenna, and consequently, the tuning network. I haven't tried doing the math or the measurements, but I would think that your cap in the tank circuit would need to handle somewhere around a kilovolt under 100 W operation. It might be worth looking at the Par End-Fedz antennas to see if you can figure out how they handle it. 🙂

  5. Hi,

    Thanks for the "QSO". Yes, I thought of that. I think Par likely uses a high voltage fixed cap and then they wind their coils to match the resonant length of their cut antennas before sealing it all up. But this is just speculation on my part. I bought one HV variable cap at a ham fest recently; I think I could use it; however, now I have to get a big toroid that can accept heavily insulated wire to wind on it--again, my speculation.

    73

    Les

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