Here's a picture of my home-made variometer. It is wound on a piece of 4" (100mm) waste pipe and the inner, rotating, coil is wound on a 3" former. The inner winding is in series with the main winding and connected between the two sections.
Here's a picture of my home-made variometer. It is wound on a piece of 4" (100mm) waste pipe and the inner, rotating, coil is wound on a 3" former. The inner winding is in series with the main winding and connected between the two sections.