This is a return loss bridge based on N6JF design. I use 2 100 ohm 1W metal film in parallel for the 50 ohm resistors permitting up to 8W power input. I use a FT37-43 Amidon core with 10 bifilar turns. The range is about 1 MHz to 1 GHz but it is practical from 1.8 up to 500 MHz. A 5*5 cm metal box is used. I use BNC but SMA is recommended as BNC do not make good contact occasionally. A small PCB was soldered under the components simulating a stripline.