Return Loss, SWR, Power Gain and Loss Calculator

A neat tool for your daily ham activities around the shack

This page describes how to build a very handy tool for quick conversion between the following parameters: gain, loss, SWR and return loss. It took me half hour to build one a couple years ago, and I have been using it since then every time I need to refer quickly one parameter to another without booting up the PC. This simple tool is very useful around the shack when doing RF designs, calculations, and measurements.

The original very neat idea comes from Patrick TK5EP, who has a PDF file available for download with the calculator artwork. My contribution was the idea of using two pieces of plastic to rigidize the design. I used one scrap CD and a blank disk, shown in the picture below.
Materials to build the RL tool

Fig 1. Materials to build the Return Loss Tool. A scrap CD will hold the base chart, the transparent disk will have the rotating piece of the calculator glued to it, and the metal round piece is to hold the pieces together.

Construction of the tool is very simple. Download and print the artwork. Using an Xacto knife, cut the window in the top portion of the calculator. Get a scrap CD and glue to it the bottom piece of the calculator (artwork facing you, the CD behind it) using a glue pen or other paper glue. Take the blank disk ( which you can find in almost any sleeve of CD recordables) and glue to it the top portion of the calculator (artwork facing plastic surface) using a glue pen applying just a small amount of glue around the blank CD center hole.
Parts of the Tool

Fig 2. Parts are ready to be put together. You have the bottom disk protecting the bottom artwork, the top disk protecting the top artwork, and a short length of a plastic, metal or wooden round alligning the disks.

Now find a suitable piece of round wooden or plastic stick, or a metal round 15mm in diameter. I used an aluminum shaft coupler which fit perfectly in the CD center hole. Just put the calculator parts together and use your mind to perfect the construction by may be securing the shaft to the bottom CD with epoxy or glue. Make sure the top piece can rotate freely around the shaft and the bottom piece. Done. Enjoy your super-puper Return Loss/SWR calculator.
Assembled Return Loss Tool

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