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Impedance Matching Test Jig 3D Printed

impedance matching test jig

Another great ham radio use for a 3D printer is making an impedance matching test jig. Cheap and cheerful. 

I recently started playing with some ferrite cores to explore various methods of impedance matching. Ferrite materials have high magnetic permeability, which means they support creation of magnetic fields. You will find this property very useful when building inductors and transformers. Everyone has a ferrite rod antenna inside an AM radio receiver, which forms your antenna.

Typically, for small signal low-power uses, you simply wind magnet wire around or through a ferrite core. The inductance you achieve is a function of the number of turns and the type of material. If you are building a transformer, impedance is matched according to the square of the turns ratio between the primary and secondary windings.

You can get a sense of the shape and size of toroid cores at the wonderful toroid information web site. You can also use an online calculator to figure out turns and wire length for inductances, as well as reactance at various frequencies.

My biggest challenge in working with ferrite cores is their tiny size. Typically, diameters of less than a half inch. Also, magnet wire is very thin, usually in the range of 20 to 30 AWG. Most hobbyists use perfboard to test their designs, but this approach requires a lot of soldering of small parts and thin wires.

So I thought I would try something different: plastic and screws.

Pictured above is an impedance matching test jig with several transformers attached. In my case, the jig is 50 by 40 mm, about 5 mm thick. Machine crews are 4-40, quarter inch long, with hex nuts embedded in the plastic base. It took about 15 minutes to design the jig in CAD and then 3D print it. All the connecting wires are simply screwed down tight.

Impedance Matching Test Jig – Sourcing Toroid Materials

You can buy various powdered iron or ferrite toroid cores on the web. Major providers include Fair Rite and Amidon. Ham flea markets are another option. Just make sure what material you are getting as performance varies considerably by frequency.

Here in Canada, I found a great source for small quantities for toroid cores: Netty Electronics run by Earl VE3AB in Ontario.


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