Good Advice on Toroids

On the QRP-L mailing list, a ham asks:

I know this should be a simple answer, but I’m having a hard time finding it. I am interested in building a EFHW coupler similar to the one on AA5TB’s site. He uses #22 AWG magnet wire.

I’m interested in using something less stout which I have on hand (e.g., #27 AWG magnet wire). Is there a calculator to determine how this would affect the number of turns on the transformer, or am I incorrect in thinking that it would make a difference?

Diz, W8DIZ, replied:

No calculator that I know of.

  1. Smaller wires have less current capacity before heating – bad thing.
  2. Smaller wires have less capacitance between windings (if same # of turns) – good thing.
  3. Wire size (for all practical purposes) does not determine inductance.


  1. Glad I made the blog. Heh. Diz is a great resource.

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