Electronics > RF, Microwave, Ham Radio

Do any free tools allow you to model RF transformers?

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Basically I want to be able to model transformers - which cannot be done with RFSIM99.

Transmission line or flux-coupled transformer? EM simulation or component simulation?

Well, its a toroid core with three windings. Two small and one large. The small ones are the supposed to be 50-or-75-ohm input and output and the larger winding (have tried six to 20 turns, currently using #2 ferrite material..) is a tuned circuit.

It's a long time since I used RFSIM99 but I think it has a transformer model built in?

I've forgotten how well this model works but have you tried stacking several transformers in RFSIM99 to make up an (ideal or physical) equivalent for your three winding transformer? Maybe it won't allow this but in theory you should be able to make up something that resembles your wanted transformer in terms of basic RF performance.

Otherwise, have a look at something like the Simetrix SPICE simulator. The free version is only limited in circuit size and you can select various transformer options including the number of secondaries, the various ratios and also the primary inductance and the coupling factor(s). These are basic models but you can add a few parasitics if you choose.

You can make some basic estimates using wave-of-the-hands transmission line theory, but the construction has to be described very precisely (pictures, drawings, winding schedule..?).

BTW, ferrites do not come in numbers such as #2: that's a Micrometals designation for mu=10 powdered iron.

To clear up confusion, check out www.micrometals.com listing of power and RF materials, and www.fair-rite.com 's listing of ferrite materials.  (There are oodles of other materials, but these two manufacturers, or their designations at least, seem to be the most commonly seen in RF work.)



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