QRA JO01OX, WAB TM23, Fists #16909 GQRP #15161 DMR-ID 2342670

Having recently bought a Yaesu FT-817ND I found myself going in search of a small portable Antenna Tuning Unit (ATU) project to build. I've never built an ATU before so it would be a challenge.

I settled on the emtech zm-2 z match for which the circuit diagram is freely available on the internet. I ordered all the parts on the internet from a combination of two suppliers.

  1. BITSBOX.CO.UK for all parts except the ones below.
  2. SPECTRUM COMMINUCATIONS for the toroids and poly-variable capacitors.

Where to start with the construction? Having never wound a toroid before I thought I'd start with the small one first. In reality the instructions where very clear and I was in more danger of poking my eye out on the end of one of the wires than getting the actual winding wrong!

The larger winding was more interesting as it is built from four distinct sections. Again the instructions where easy to follow and resulted in a nice looking winding. I held the winding together with two small cable ties connected back to back and placed on the outside edge of the toroid.

Note: In retrospect I would have made the two twisted connections longer - ends 2 and 3 in the construction notes. If they have been a centimetre longer then the final soldering of the toroid would have been easier.

Next I turned my attention to the layout of the controls and the drilling of the holes. I drew the layout of the controls on a piece of graph paper and arranged them to match the layout in the instructions. I maked the centre for all the holes and wrote on the required drill size. This paper was then glues onto the box top using a water soluble glue so that, once drilled, the paper and glue could easily be removed.

Finally the build for real began. I followed the steps as layed out in the instructions and the following three pictures so the build at the end of each phase. There were no real issues to worry about. Phase two was interesting as the project took on a three dimensional feel when the SWR bridge was constructed. I spent a lot of time working out just where the resistors would fit and how far away from other components they would be - time well spent I think.

Once complete it had to be tested. Thanks here must go to Peter G8BLS who took charge and armed with an FT-817, a G5RV and some patch leads put the device through some tests. Thankfully he concluded that it worked!