Topband: 1:2 UNUN

[Richard (Rick) Karlquist]

Maybe this will help:

I use a 1:2.25 Unun (3 to 2 turns ratio).  It will match 22.2 ohms
to 50 ohms.  It is wound on a single 2.4 inch diameter core of 77
material.  A pair of RG-58 coax cables are wound around it in
tandem.  I put on as many turns as would fit ... about 10 turns.
The shields of the two coax cables are wired in parallel.

This results in essentially a trifilar winding (1.  The shields;
2.  One of the center conductors  3. The other center conductor)
This trifilar winding can then be connected in the usual way to
get a 3 to 2 turns ratio autotransformer).  The order of the
connections is:  center conductor #1, then the shields, then
the #2 center conductor, in series.  The radio drives
the 3 windings in series, and the antenna is tapped down to
utilize only 2 of them.  I run this at 1,500 watts in
contests with no problems at all.

The concept is extensible to a quadfilar winding constructed
from 3 coax cables in tandem (shields in parallel).  This can
be wired with a 4 to 3 turns ratio resulting in a 1:1.77 UNUN.
This matches 28.125 ohms to 50 ohms.  An alternate modality
I have used is to use two coax cables as in the 1:2.25 UNUN,
but make one of the coax cables from tri-ax.

I can highly recommend UNUN's for the convenience factor if
your drive impedance is compatible with the available ratios.
They are broadband, no tuning.

73
Rick N6RK

On 1/17/2022 6:18 AM, Kenny Silverman wrote:
> Does anyone have a drawing on how to wind a 1500w 1:2 UNUN?  And what type of core is needed?
> 
> This is for my 160m vertical which is about 28 ohms.
> 
> Regards , Kenny K2KW
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