Filters for power supply lines are measured according to CISPR 17, annex C (respectively DIN EN 55017, annex C).
Two wideband transformers are required to transform the typical impedance of measurement devices from 50 Ω to 0.1 Ω or from 50 Ω to 100 Ω respectively.
The 0.1 Ω transformer (voltage division ratio 22:1) has to be connected to the 50 Ω generator. The 100 Ω transformer (voltage division ratio 1.4:1) has to be connected to a 50 Ω receiver.