You actually can overlap RX and TX bandwidth on coax, though you need magic-tees and very good impedance matching in either end, and of course constant impedanc

You actually can overlap RX and TX bandwidth on coax, though you need magic-tees and very good impedance matching in either end, and of course constant impedance cable. That limits it to about 100 Mbps, but you can buy the (magnetic) magic tees to do it. These are specifically for replacing analog video cameras with IP over the existing coax.