I got some TAIYO YUDEN 9012R0 LEADED COMMON MODE CHOKE COILS FOR AC LINES and thought some uses for them. The specifications for those from datasheet were:
TLH10UA 901 2R0 RoHS
Common mode inductance (mH): 0.9 min.
Normal mode inductance (mH): 0.067
DC resistance: 0.089
Rated current (A max): 2.0
Rated voltage AC (V max): 250
I did some measurements to see if those could be used for signal isolation transformers. I did some measurements.
Inductance one coil open, measured on other coil: 1.33 mH
Inductance one coil shorted, measured on other: 0.01 mH
Frequency response was quite OK well beyond 10 MHz.
Then I though could those pass Ethernet signal?
At least basic specs looked “close enough” to what Ethernet needs.
I did a test where I wired that common mode choke as signal isolation transformer to one wire pair of Ethernet. The 10M and 100M Ethernet use two wire pairs (pins 1,2 and 3,6). I wired this device being tested to one Ethernet direction to pair that connects to pins 3 and 6.
It seems that at least with just few meters lomg cables the Ethernet communication seemed to work with 10M and 100M speeds.