Plain-language answer: A Ruthroff transformer connects transmission-line sections so part of the output voltage is added in series to obtain an impedance transformation.
Why the real component differs from the ideal
It can be broadband, but high-frequency response and common-mode behavior depend on line delay, winding, core, and connection topology.
What to verify
Confirm the exact Ruthroff schematic, impedance ratio, balance requirement, frequency, load, and power before construction or substitution.
The common mistake
Calling any autotransformer winding a Ruthroff transformer.
Component boundary
Use frequency-specific ratings and the exact topology, material, geometry, load, power, duty cycle, and cooling. Begin at low power and stop for heating, odor, arcing, distortion, or unstable measurements.
