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Saturday, July 14, 2018

Homebrew Tuner for Doublet Antenna

For now, I've put the Moxon project on the back burner.  I will take it up again once Old Sol starts showing some spots.  In its place a 135 foot doublet is going up.  I got at a hamfest a while back.  (It is the only HF antenna that I ever bought!) It is the SPI-RO Manufacturing Company's Model A-10.  It came with 100 feet of 450 ohm window line.   It will be up on the roof soon.  

Today I put the tuner on the wall in the car port right outside the shack. I even built a little shelf for the SWR meter (used one of those Whole Food grilling planks!).  I put a 25 ohm resistor where the feed line will connect.  I was able to tune it up on the two bands I tried: 40 and 17.  

There is a smaller coil inside the big one -- the smaller coil resonates with the lower variable cap. 

You can see all the homebrew rigs in the background -- waiting patiently for the antenna.  

I actually built the tuner back in 2012, but never used it.  Description here: 

I will try to provide a schematic and more details soon. 


  1. Nice give the schematic pse 73

  2. You really should try a big magnetic loop as it might help with your local broadcaster as well.

  3. Also check out swing link or swing coil coupling.
    You can change the coupling by moving the coupler in and out of the main coil or rotate it like they used it in vintage gear :-) Like this https://www.ebay.com/itm/VINTAGE-RADIO-TUNING-CAPACITOR-COILS-LOT-OF-2-SC851A-SC118-ROTATING/252350665725?hash=item3ac14593fd%3Ag%3AS%7EcAAOSwSzdXCkGT%3Asc%3AUSPSPriority%2193022%21US%21-1&_sacat=168088&_nkw=vintage+radio+coil+rotate&_from=R40&rt=nc&_trksid=m570.l1313&LH_TitleDesc=0


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