lightweight inductor

NOTA BENE: Since working out that my aluminium foil tape is probably less than 0.075mm thick and therefore probably much more resistive than 1mm diameter wire, I will create a new design using wire instead. When I have, I will update this page.

When I first constructed a balanced L-match (see image) to use with my inverted vee antenna, the inductors I constructed using aluminium wire were usable, but the turns were too flexible and close-spaced. When I last used that antenna (end of 2009), I promised myself that I would construct some better ones. The intended inductance of each unit is somewhere between 30 and 40 microhenries.

It is now August 2011. I recently did some prototyping, and now I am about to commence construction of the final units. However, such progress is often hindered by something unforeseen, so I’m writing this up before it’s done, so that the sharing of the idea will not depend on its implementation. I will provide pictures when there is something to see.

First, take a piece of PVC sheet of approximately 500mmx100mmx0.4mm. Before bending this into a former of diameter 150mm and fixing the join with staples and/or glue, describe the path of the coil with marker pen and ruler. 15 turns in 75mm. Also, make incisions on both sides of each tapping point, just long enough for the width of a paper clip to pass through. Extra tapping points can be made later, but this is the best time. Stagger tapping points so that adjacent ones will not touch.

The conductor will be cut from a roll of adhesive aluminium foil tape. The length required is about 7.19m, so cut a strip longer than that, about 2.5mm wide. This might be tricky, but at least the backing of the tape provides some security.

Stick the tape along the lines inside the former, from one end of the coil to the other, peeling off the backing as you go. The flexibility of the PVC should enhance this process.

Finally, pass each paper clip through one slit, across the conductor and back through the other slit. Connections made using this technique appear to be good.