I assume you want to measure them on a 50 ohm test system. A bit mathy, but
you could use a minimum loss T pad and include the pad's loss in the math...

For a transformer, ther turns ratio would be square root two...
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Steve N, K,9;d, c. i My email has no u's.

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I'm testing some 10/100 ethernet transformers and I need a 50:100 ohm
balun for 30 - 80 MHz. How do I make one? (I need to measure return
losses on the transformer. The spec is LT -18 db.)