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I need to build another 9:1 unun and I start searching for my toroids... (I have build 2-3 something like 4 years ago)... In parallel I checked on Google about the correct toroid etc so I found 2-3 pages with designs. My focus is on power loss as I run QRP on batteries.

9:1 voltage unun using a L15 ferrite core

9:1 Voltage Unun - FT240-61

9:1 voltage unun using a T-200-2 powdered iron toroid core

What do you think regarding power losses and materials? Which toroid should I use? (I already have the *-61 and the *-2).

Regarding wires for the turns, some use enameled copper wire, some 3-colour for like a power socket.

The unun is not for portable. So a size 200-240 is okay for some future proofing.


If I can get ok losses down to 80m, I'll be very happy, I mainly use 15 to 40m.
It's for a “random wire” end fed. Probably around 58ft max. Or maybe 53ft (space restricted)

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  • $\begingroup$ Welcome to this site! The [balun] tag also covers unun, so I added that. $\endgroup$ – Mike Waters Feb 20 at 21:55
  • $\begingroup$ This is for an end-fed antenna, right? Is it the same antenna for all those bands? How long is it? $\endgroup$ – Mike Waters Feb 21 at 2:19
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    $\begingroup$ Its for a “random wire” end fed. Probably around 58ft max. Or maybe 53ft (space restricted) $\endgroup$ – OHTO Feb 21 at 7:43
  • $\begingroup$ You might find this similar question and the answers particularly useful. On some bands, a 9:1 transformation ratio (50 ohms to 450 ohms) might not be optimal, as the feedpoint impedance might be much higher or much lower than 450 ohms. $\endgroup$ – Mike Waters Feb 21 at 13:36
  • $\begingroup$ I copied your comment with your antenna info into the answer. Note that comments are not searchable, and such details should be in the answer itself. $\endgroup$ – Mike Waters Feb 21 at 13:56

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