A QRO tandem match for the amplifier build
A directional coupler for the amplifier. In this post we take a look at the directional coupler I built for the amplifier. I wanted a built-in coupler to measure power and have SWR protection. I built a tandem match coupler. Why, you might ask? Because I’ve built one before with good results, and after struggling with a Bruene coupler design(which I could never get to work properly), I decided to stick with what I know works. Schematic representation of a tandem match. The transformers are wound on ferrite toroids where the primary is one pass of coax thru the center. Note that the turns ratio needs to be the same for the transformers, even though the cores may differ. Theory in brief (with disclaimer) Expect no in-depth math here. This is a simplified explanation and more of a picture series on how I built mine, along with some thoughts on how to improve it. A tandem match coupler works by sampling both current and voltage in the transmission line using transformers: T...