Thanks for the question. First, let me clarify, the only connection between the topside and the ROV is through the Fathom-X boards (and just two wires). There is no RS-485 unless you add it to support something else. The tether does have extra twisted pairs for that.
You can absolutely replace the Fathom-X connection with a standard Cat5 Ethernet cable. There are a few primary reasons that we use the Fathom-X boards:
- Uses only 2 wires instead of 8 wires, making for a simpler tether.
- Can handle much longer distances than regular Ethernet, which is limited to about 90 meters.
I hope that answers your question.