I had just purchased and built a Z-match QRP tuner from Emtech, the performance and its ability to tune just about anything I could hook a wire to, made it the perfect tuner for QRP field day or back packing.
I was so impressed by the design I just had to have a Z-Match for my shack. I found a single coil Z match design by Lloyd Butler (VK5BR) online and decided that this would fit the bill.
Original circuit diagram from VK5BR
Everything for this project was either homebrewed or came out of my junkbox. I started with the air variable capacitors. The first capacitor was a single gang 20-350 pF. Using a program by VE3SQB for designing homebrew capacitors, I came up with the specifications for the capacitor at C1. I cut out the rotor and stator plates from a piece of galvanized sheet metal left over from hurricane Charlie. This was not the best choice as my hands are still covered with blisters and scratches from the sharp edges and the tin snips.
I needed a better idea for C2 which was a two gang 2x20-230 pF cap, and decided to try aluminum flashing used for roofing. I purchased a ten ft roll for $7.00 and two 36” threaded rods at $2.00 each from the local Home Depot. The aluminum was a bit flimsy during assembly but stiffened up as the capacitor was completed. The stator and rotator plates are mounted on 1/8” threaded rods using #8-32 nuts as spacers.
Now that the two capacitors were complete I could concentrate on the coil which was relatively easy. I stripped the ground wire out of a length of 14-2 Romex house wire and wrapped the bare copper approximately 16 turns on a 1 ½” PVC form. This would be used at L1. I did the same for L2 using 5 turns. Next step was to drill two rows of 14 holes in a rectangular piece of acrylic (plexiglass) 1 ½” apart and spaced ¼” between each hole. And then two more rows of 4 to form the outside coil L2, which is approximately ½” larger in diameter than L1. Threading the acrylic form was simple and makes a neat sturdy coil.
Original template from VK5BR
For L3, I used a ½” PVC form and wrapped eight turns leaving one end about 6 inches long. L3 is connected to the antenna load side and can be bypassed using an off on switch.
I found a small piece of ½” plywood for a base and sprayed it with a coat of clear lacquer. I also located a used SO-239 and two binding post in my junkbox. The off/on switch came from Radio Shack and cost under $2.00.
With all the components complete and small parts located, it was time to start assembling the tuner. I started by mounting the coil L1 & L2, then the capacitors making my solder connections along the way. The last parts mounted were the SO-239 for the coax connection to the rig, the binding post for the antenna load and finally the off/on switch for S1 which is located on the face plate of the tuner.
The front face plate is a piece of acrylic which was drilled to accept the switch and capacitor tuning post. I used two screw tops from a couple Mountain Dew bottles for the capacitor tuning knobs which are held on with nylon lock nuts. This completed the tuner.
For the first test I hooked up the twinlead from my 135 ft. doublet to the binding post and then the coax to my MFJ 259-B antenna analyzer. I could easily tune all bands from 10-80 meters with a SWR of 1.3:1 or less, and only had to use switch in L3 for the lower part of 80 meters.
Now for the real test, I moved the coax to my Kenwood TS 180-S and easily tuned 10, 15, 40 but could not get a match on 20 or 80 meters. After adjusting the length of my feedline I could get acceptable matches on all bands.
Overall, I have less than $15.00 invested in this project making it the most affordable piece of equipment I own.
