This transformer can be used for VHF and UHF reception (from 50 to about 800 MHz). The input is 300 ohms balanced and the output is 75 ohms unbalanced, ready for coaxial cable connection. A device similar to what is presented here is used in commercially available antenna preamplifiers with 300 ohms input.
To build it you need a toroidal core with an outer diameter of 8 to 16 mm and a few copper wires of 0.3 to 0.5 mm diameter (you can use wires from UTP network cables). You will make 2 by 2...3 turns as described below.
|What you need|
Besides toroidal cores, if you have available, you can use double hole pig-nose cores which are specifically designed for radio frequency. Here is a photo of a ready made antenna amplifier that uses such transformers. As you can see, they left the input ground not connected.
|Pig nose core matching transformers|
- A russian page about reception preamplifiers with 300 ohms input: Новые антенные усилители.