Help: how to design air-core transformer?

The old Motorola App Note AN1304 discusses the use of coaxial baluns around 1GHz, to reduce Z mismatches of 100:1 to approximately 6:1.

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also

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......don't forget to check references listed in tha articles.

Going to 50ohms in the first place, may be part of the problem, as your active devices likely exhibit output impedances in the 10ohm range or less, to begin with. Matching earlier may help.

If galvanic isolation is required, a simpler 1:1 or 2:1 conventional balun transformer might be introduced additionally, in a convenient position. because required turns are low, you might consider winding shapes that are not normally seen in baluns - perhaps a single loop inside an isolated screen (~output winding).

With the app data aimed at achieving 50 ohms, it may be difficult to turn it around to make sense for low load values such as 0.5 ohms.

RL

Reply to
legg
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It isn't clear (to me, anyway) why you are specifically seeking an air-cored solution. What is the problem with a ferrite core? You can get a very good match with a 3:1 turns ratio, or if you really want to get precise then increase the turns so you get M:N ratio closer to SQRT(10).

Reply to
budgie

Ah, that's easy. You want a tuned impedance matching network, or perhaps a tuned transformer, or a tapped resonator, etc...

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And I did find an amazing report of a modestly wideband (15%) 50-ohm to 1-ohm transformer, working from 1200 to 1400 MHz.

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One thing, keep in mind that 0.2nH of inductance is more than 0.5 ohms at 500MHz. Watch out. Do you know what you're doing?

--
 Thanks,
    - Win
Reply to
Winfield Hill

increase

I switch to ferrite core now. Could you please tell me what is the upper frequency limit of ferrite core? I heard from someone that the limit is 200MHz.

Reply to
Jim

Note also the links to course notes, transmission line and Z-matching SW by Trueman at Concordia and Pozar at Amherst;

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RL

Reply to
legg

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Awww ferk - misread that bit didn't I ....

Reply to
budgie

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