https://www.epanorama.net/circuits/teleinterface.html
Traditional transformer hybrid circuit
updated model
https://en.wikipedia.org/wiki/Hybrid_coil
https://en.wikipedia.org/wiki/Telephone_hybrid
https://www.epanorama.net/circuits/teleinterface.html
https://en.wikipedia.org/wiki/Hybrid_coil
https://en.wikipedia.org/wiki/Telephone_hybrid