How to select the impedance of the common-mode choke for the network port of an edge computing box?

When selecting the common-mode choke impedance for edge computing box network ports, the principle should be to maximize the common-mode impedance in the interference frequency band. For Gigabit Ethernet, which mainly radiates in the 100-500MHz band, a common-mode impedance of 90-120Ω is recommended for 100MHz. A model like CMZ2012A-900T (CM common-mode, Z impedance 2012, size 2.0×1.2mm) and 900T impedance of 90Ω for 100MHz are suitable. If interference is concentrated in the low-frequency 30-50MHz range, CMZ3225A-201T (200Ω) for 100MHz can be selected. However, it should be noted that excessively high impedance may degrade the signal eye diagram; generally, an impedance of 90-220Ω is selected, and signal integrity should be verified. For 100Mbps network ports, CML3225A-510T (inductive type, 51μH) with an impedance of approximately 1kΩ is suitable at 10MHz. Furthermore, it is important to note that the rated current of the common-mode choke must be greater than the interface power supply current; for example, PoE requires >0.6A. The CMZ2012A's rated 0.8A is sufficient. After selection, the differential-to-common-mode rejection ratio should be verified to be >20dB through TDR testing.