Topband: 1:2 UNUN

[Wes]

I'll second Rick's approach, although I've not incorporated it yet.  I built a 
parallel wire transformer per Sevick Fig 6-11.  It measures just fine.  Until 
it's installed I'm using an inverted-L with a shortened top wire which makes the 
feed capacitive.  A shunt inductor forms an L-network and is a built-in static 
bleed.

Wes  N7WS.

  On 1/17/2022 11:34 AM, Tim Duffy wrote:
> I match my 26 ohm feed point with a simple L network. One series coil then a
> shunt capacitor. Steps up to 50 ohms perfectly.
>
> 73
> Tim K3LR
>
> -----Original Message-----
> From: Topband [mailto:topband-bounces+k3lr=k3lr.com at contesting.com] On
> Behalf Of Richard (Rick) Karlquist
> Sent: Monday, January 17, 2022 1:10 PM
> To: Kenny Silverman; TopBand List
> Subject: Re: Topband: 1:2 UNUN
>
> 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
>
>