Z-match antenna tuner

This article describes my DIY attempt at building a manual antenna tuner. This is based on the plans for the ZM-2 tuner as sold by Emtech.

My version suffers from considerable parts substitution, as I was building from whatever components I had available that seemed “near enough”. So caveat emptor if you follow my example!

That said, initial bench testing confirms it’s able to match a 9:1 long wire to a near 1:1 SWR.

Note that the original ZM-2 design is rated for 15W, and my version is similarly, perhaps lower, specified.

See this video for an example of using the ZM-2 tuner.

One significant change that I made to the parts list (and not for the better) was to use a locally available variable capacitor. The original used a dual gang 266 pF variable capacitor, but mine are only 60-160 pF.

UPDATE: I rebuilt it using 270 pF variable capacitors that I bought online. It now tunes much easier over a wider range.

I also went a bit overboard on the enamel wire, but that’s just what I had on hand.

The next substitution was using a stray red toroid rather than the T130-2 from the ZM-2 parts list. I’m assuming my substitution is also type-2 material as it’s red, and when I acquired it the previous owner had used it for a 9:1 matching transformer. The OD is 1.5″, ID is 1″, and height is 3/4″.

Also substituted was the FT32-43, for which I instead used an L8 toroid from Jaycar. I don’t think this is critical as it’s only used on the SWR sense circuit.

More concerning perhaps is that I used 1W carbon resistors instead of the specified 2W components. I’m only planning to use this with a small QRP transceiver, with a maximum of 5W output, so I expect this is ok.

I used a slightly smaller box that the one provided in the ZM-2 kit, so I had to locate the small toroid between the two variable capacitors. Just a blob of hot glue to keep it in place.

I mounted the main transformer atop the variable capacitors. Again with a blob of hot glue, but also the six wire connections to keep it in place

Next I connected it to a 9:1 matching box and a 13 M length of wire. It was able to tune up both 40M and 20M easily enough.

Here’s a photo of the SWR after tuning for 20M.

Note that I’ve only tested it on the bench so far. I’ll add an update after I get it out in the field with the intended transceiver.

PS/ If you want to build your own version the original manual is here.