Case study – effectiveness of the EMI filter
The following two screenshots illustrate a conducted emissions measurement with the R&S®RTM3000 oscilloscope – without and with an EMI filter.
Channel 1 displays the measured time domain signal connected to the LISN. Due to the LISN, this signal is attenuated by a factor of 10 dB, which has to be taken into account when comparing measured values with emission limits. The bottom window shows the spectrum in dBuV on the input terminal of the power supply. Without an EMI filter, the noise spectrum generated at the input of the DC/DC converter is clearly visible. In contrast, the measurement with an EMI filter shows that the conducted emissions on the input line are effectively attenuated.
For some frequencies, up to 30 dB attenuation is visible.