The DK7ZB 12 to 50 ohm coaxial matching transformer
We’re not going to republish excellent already published materials from known experts.
Authors such as DK7ZB need no introduction, so we’ll link directly to the page here. For HF you’d normally consider a hairpin match, but at VHF and UHF this fully symmetrical solution is king.
You can find all the info you need to create a world-beating 12 to 50 ohm match with ease.
For a 12 to 50 ohms impedance transformation, 2 equal lengths of 50 ohm coaxial cables are used. Link below.
A Simple Modification –
Changing a ‘4 to 1’ Balun into a ‘1 to 4’ Balun
As an alternative, here’s a simple modification to change your 4:1 Guanella Current balun into a 1:4 Guanella Current Balun. This type of balun can be ideal for low impedance Yagis or any other antenna where an impedance transformation from 12.5 to 50 ohms is required.
Take a look here at our article on designing a good high-power 4:1 current balun, then come back to this page. Below is the simple wiring requirement.
If you think about it, let’s reverse the input and output so rather than a 4 to 1 impedance transformation [200 to 50 ohms], we swap it to a ‘1 to 4’ impedance transformation – that’s 12.5 to 50 ohms. In essence what was the ‘output‘ now becomes the ‘input‘ and vice-versa. All pretty straightforward really, but here’s a diagram that simplifies the description.