Homebrew KW Antenna Tuner

What is the best full legal limit transmatch, antenna tuner available? The one you build yourself. Here is how to do it. You may want to use wood for the case, if you are handy with that medium, to save cost. Be aware of shock hazard if you leave it on a simple horizontal wooden "breadboard" style. I had a nice 19" rack cabinet and like to work with sheet metal. Dials and knobs are all WW2 surplus from my junkbox.

This is the homebrew Murch style transmatch I built to work with the new K7DYY AM transmitter for 160 and 80 Meters. It is the Super Senior model. I built this in two days from items I had in my junk box.

The input and output capacitors are 500 pF. The roller inductor is 26 uH but you could probably make do with 20 for 160 Meters. Be sure to get one with heavy wire to handle the power.

The turns counter and capacitor vernier knobs are from WW2 surplus.

Even though the new rig is modern, I still like a vintage look for the station.

Yes YOU can build a transmatch just as nice as any commercial unit if you shop frugally and are handy. You will save a lot of money and get some satisfaction of creating your own equipment.


Update 8/30/2014

After a test run with the new K7DYY transmitter, I also used the new transmatch with the Valiant on higher bands. I added a small coil in series with the roller inductor to ground to prevent adjustment of inductance to zero. This prevents damage to the roller inductor or transmitter. I added coax RG-8/U on the input and output connectors to the tuning capacitors to eliminate inductance in series with the capacitors. A minor improvement in efficiency on 10 and 15 meters was observed.


Update 11/21/2014

If you cannot obtain the parts surplus or at hamfest, you can purchase those employed in the MFJ-989D brand new directly from MFJ for less than $200 total. This is half what you would pay for the full MFJ 989D. That includes an antenna selector (I prefer an Alpha Delta Switch for reliability) and a power meter (I prefer a separate power meter like the Ten Tec KIT #1225). If you already own these items, why pay for them again? Just build the tuner in a separate box, which is the best way, IMHO.

The Ten Tec power meter kit is pricey at $160, You can also get a fully built and calibrated one of various brands for similar prices. I was able to get good correlation between my digital wattmeter and the TT 1225, unlike the eham reviewer who complained.

The Alpha Delta antenna switch is without compare. There are Daiwa, which are pretty good, and MFJ and Diamond. Any of them employing a leaf switch in a machined housing are better than a conventional ceramic rotary design as used in the MFJ-989D or the old Heathkit antenna switches. The plating rubs off and the contact resistance becomes intermittent and high because the base metal is not reliable any more. Use a separate antenna switch. If it fails, you can replace it without having to do it inside the antenna tuner box with expensive proprietary parts.

This is not to badmouth the MFJ 989D. For the price ($410), all assembled, it packs a lot of features and value into one box for a good price. You even get a small 300 Watt dummy load. It has a much better matching range than the Ten Tec 238C which is $819. See my article on rebuilding a burned out 238B for the inside story. The antenna selector inside the TT 238 is a cheap rotary switch, not an Alpha Delta. The Heathkit SA2060 is the same antenna selector. Everybody does it this way to save cost. Buy the best separate pieces, roll your own, I think.

Here are the parts to roll your own if you still want to:

  • MFJ 282 -2020 TWO NEEDED
  • 40 - 493 PF @ 1500 V AS USED IN MFJ-989D ($71 EACH)
  • MFJ 404-1010 one needed
  • 22 uH Air Roller Inductor as used in MFJ-989D ($54 EACH)

Depending on what you want in style, the turns counter and crank and reduction tuning knobs and indicators are all available from MFJ also. You may have these in your junkbox or from a hamfest to get an old buzzard look like mine.

You also could check Surplus Sales of Nebraska to see if their parts suit your needs and purse.

What is the best antenna tuner transmatch? One you build yourself, in my opinion.

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