RF transformer design

[K8DI]

Can anyone point me to a reference on transformer design? There’s a fair amount on the web for power transformers, but I don’t find much for RF. I’m looking for target inductance, core selection criteria, and so on. Not rules of thumb like use mix 73 for 40 meters, but rather, numbers and calculations. Anyone know a good book? Or personal knowledge/training/design experience?

Ed

[W4AMV]

Start with 2 texts. Not the end all but loaded with good references.

J.Sevick, Transmission Line Transformers

DeMaw, Ferromagnetic Core Design and Application Handbook

and one chapter, chapter 12 in an excellent text:

Solid State Radio Engineering, Krauss, Bostian, Raab

Alan

[K8DI]

Thanks for the quick reply. The DeMaw is in the local college library, and I found the Krauss book online for $5, so I guess I'll be doing some reading!

Ed

[WA1MNQ]

Hello Ed,
                Do not forget simple coil coupling, remembering the ratio you want. Like air wound coils and no cores. We make our own and repair substantial sized transformers in addition to repairing the induction heaters at work and we do units up to 600 kilowatts. Also as small as 1 kilowatt.
In the frequency range of most induction heaters, 455 Khz you do not need a core.
Lower frequencies like 50 Khz do require a core. In between, yes likely.
But when you go into the Mhz range like we do in ham radio, not required unless size is a major issue.
We use typically 3/8 inch soft copper flex lines and run water through for cooling the copper because we run hundreds of amps for current. Sometimes we want only a couple of ohms in the target load.
Just saying, simple is sometimes easy and good.

Mike, WA1MNQ

[W4AMV]

Hello Mike, Ed. Thanks for the heads up on the auto transformer as well for Z matching.
I should add, the Solid State Radio Engineering Text, see Chapter 3, has an excellent section treating the approach of BB Z transformation via the RF transformer without the core. Also, the text is available as a pdf down load, see below: Although I prefer a printed version!


http://www.csun.edu/~ih20409/SCHOOL1/Solid.State.Radio.Engineering(Krauss.1980).pdf

Alan