Filters for power supply lines are measured according to CISPR 17, Appendix C (according to DIN EN 55017 Appendix C). This requires two broadband transformers that transform the typical measuring device impedance from 50 Ω to 0.1 Ω or to 100 Ω.
The 0.1 Ω transformer (voltage transformation ratio 22: 1) is connected to the 50 Ω generator while the 100 Ω transformer (voltage transformation ratio 1.4: 1) is connected to a 50 Ω receiver.
Please note: The transformers must not be connected to power supply lines or DC voltage sources!