MoCa - Ethernet over Coaxial
Begin from reading a datasheet on something like this:


Microchip's FastECoax7501


IMO, it's a good way to meet the technology, including the first time.

To build a modem on this chip, you also need a 100BASE-TX to 100BASE-FX converter/switch IC, but this is not a problem too because there are many solutions on the market today.