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End-Fed Half-Wave Tuner for QRP

A "Summit-On-The-Air" Pocket Sized Tuner

From Better QRP, Kitted by Stu, KI6J

Since I have started getting interested in QRP again (after thirty years or so) I have been looking at the various kits for radios and accessories that are available.
One simple kit that looks very useful is an End-Fed Half-Wave antenna tuner from Better QRP. These were designed and kitted by Stu, KI6J.

I got interested when I started building a Rockmite for 7030 KHz and wanted to include a tuner in the package to allow using a simple wire antenna. This compact tuner seemed to be just he thing I was looking for. At $26 for the kit, the price was right as well. I have actually built two of these now; the one built into my Rockmite project, and another built to use with other QRP radios.

I knew I wanted one for the Rockmite project, and probably another for general QRP use. By what turned out to be a lucky faux pas, I was encouraged to get a second one right away. The original kit that I ordered had not arrived after a long time, so I contacted Stu and he promptly sent a replacement, with a case kit to compensate for the delay. Of course, before I finished assembling the replacement the original arrived, after side track through the USPS worm-hole. I paid Stu for the second kit, and finished assembly in parallel.

The two transformers that need to be wound, one on toroid and the other on a binocular core, were pretty easy, and anyone who has wound inductors before will have no problem. If you have never wound an inductor before, just follwo the directions carefully and use the photos in the manual as guide and it should be no problem. There is enought wire included for a couple of attempts at each.

Soldering on the surface of the board takes some patience, but was not difficult, once I started tinning the pad and the component lead. You do need to be mindful of lead length and how the component will lay or stand on the board, but it is not a great challenge.

After assembling the first one, I tested it as shown in the directions, using the 4.7K "dummy load" resistor. The adjustment is a bit touchy, and the target point is narrow, but not extremely so. I adjusted it first with a 1 watt 7050 KHz signal; once the LED went out I switched to the operate position and checked with my MFJ-259B. It consistently tuned to less that 1.1:1 with the LED out in the tune position.

Since I plan to use the one in the Rockmite only on 7030 KHz, and the one in the separate case mostly on 40 through 20 meters, I left the trimmers on the cap engaged about half way. This shifted the tuning range down to 6.440 to 18.960 MHz. Adjusted like this it doesn't cover 15 meters, but it gets the target point for 40 meters off the bottom of the cap's range. With the trimmers adjusted as described in the instructions the tuning range is 6.999 to 22.475 MHz with the supplied "dummy load" resistor.

With 67 feet of wire arranged as a sloper in my backyard, the tunable range was from the lower band edge to 7238 KHz with less than 1.5:1 SWR. The upper band edge was 1.9:1. The SWR was 1:1 at 7080 KHz. As you get away from the apparent resonant pint, the minimum SWR that you can tune to creeps up. This was with the tuner velcro'd to a plastic folding table about 42 inches off the ground and the other end in palm tree roughly 30 feet tall. I haven't made any contacts as yet, but was able to hear CW, various digital modes, and SSB.

The circuit is very simple, and works very well. Even if you don't normally build kits, this is a very useful tuner, and very easy to build. Stu, KI6J, was very friendly and helpful. Service couldn't have been better.
This is an easy one evening kit, that is very useful and a great solution for QRP operations...

Last updated 6/15/18