Printed Inductors - Continued

To learn more information about Printed Inductors (see previous post) I decided to check the self-resonate frequency - by disconnecting the capacitors. This experimental coil is self resonate at 22.2mHz.

Scale = 1 to 41mHz
 Resonate at 22.2mHz

Above 60mHz all kinds of strange minor resonate modes occur.

Note: Flat-topping on the graph is over range.

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Printed Inductors

Today I started experimenting with Printed Inductors, which is something that I have always wanted to try. The idea is to print and etch inductors directly on the PCB, many commercial products and some kits use this technique.

For my first experiment I created a 25.5 Turn Inductor with a single 5mil spiral trace, 12mil centre-to-centre spacing, within a 1 inch diameter. The tuning capacitors are soldered to the upper two pads.

 A Tuned Tank Circuit

Note: it is difficult to see the spiral with the naked eye, it is just a blur of shiny copper.

This is the Centre of the Spiral Conductor

My goal was to resonate at my favourite QRSS frequency of 10.140mHz. With the help of a 47pF cap and a parallel 4-50pF trimmer, resonates was obtained on the desired frequency.

I thought the distributed capacitance of the spiral and of the 32mil double sided PCB would kill the Q of the circuit, but it seems to do well as indicated on an AIM-4170B Analyser. But, this will need more investigation.

Scale = 8 to 12mHz

I may have to plan a project using this technique for the tuned inductors.

As I have time, more experiments and information on Printed Inductors will follow!

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