Perhaps a "hair pin" match? I used a hair pin coil at the base of a vertical that was 35 ohms.
73, Mike WA5POK On Monday, January 17, 2022, 01:36:12 PM EST, Tim Duffy <k...@k3lr.com> 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....@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 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 > _________________ > Searchable Archives: http://www.contesting.com/_topband - Topband Reflector > _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector