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Homebrew Z match ATU finished

December 5, 2008

Homebrew Z match antenna tuner

My main antenna is an 88ft doublet, so I need to use a tuner with my rigs.  The K3 and K2 have built in antenna tuner units, but the other QRP rigs do not.  I have the Emtech ZM-2 tuner but I also wanted another efficient tuner for the shack.  Over the last few years I have picked up coils and tuning capacitors at hamfests.  Using some of these I recently assembled a Z match tuner, shown here.  The tuner includes a Stockton bi-directional wattmeter (again homebrew), so that forward or reflected power can be monitored.

Looking down on the tuner.

All the tuner parts come from the junk box and have been collected at low cost from hamfests etc.  Even the piece of oak the components sit on was part of some cheap off-cut sold at a local timber merchants.  The front panel was a piece of plastic that was easy to drill and work for mounting the switch, panel meter and capacitor shafts. Overall cost for the tuner must be below $20 for parts.

The tuner works without using the extra capacitors, that can to be switched in or out, which are commonly found with these tuners.  That said, I cannot get it to tune on 10m. From 80m to 12m tunes to below 2:1 SWR, but not 10m.  This is not a critical loss as I will mostly use the tuner on 80m to 20m.  The coils are air wound and if you look closely you can see one is made of insulated wire overlaid on the primary coil.  As long as this primary does not become hot the overlaying should work well.  I have checked for heating after periods of testing the tuning and have not felt any heating of the coil.  I am hoping this is an efficient tuner.

Close-up of the Stockton bi-directional wattmeter circuit.

As mentioned the meter is a Stockton type which is constantly in the circuit so you can see the forward or reflected power as you use the tuner on the air.  The direction of the power shown on the meter is set by the front panel switch. To tune select the reflected power and adjust for the lowest deflection of the needle.

I will post more details and a circuit diagram later.

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2 Comments leave one →
  1. KI5BC Rynn permalink
    December 20, 2010 9:02 pm

    I have quite a few coils and caps just waiting for a new coupler. Can hardly wait for your schem. Happy Christmas, OM! de….Rynn in Sunny South Texas

    • va3stl permalink*
      December 20, 2010 11:43 pm

      Rynn,

      Wait no longer, I put the schematic of the tuner in this post. There are links towards the end of the post that are worth reading too before building.

      A Merry Christmas to you too Rynn and all the best in 2011 for you and your family.

      Alan

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