There is no way to get something like a passive coupler for RG6 to RJ45 - you are talking about effectively taking 2 wires (RG6) and trying to convert it to 8 wires. Can't be done.

[Mike Lu] likes to add serial ports to his routers to use for debugging but he didn’t want to drill holes in his new RT-N12. After a bit of head-scratching he thought about repurposing the fo… ...

That’s why many think a smaller Ethernet connector would be desirable.” The connector most likely to replace the RJ45, Messerer says, is the ix Industrial interface. This connector features 10 ...