How would you combine DC power, bi-directional serial data, and an RF signal on a single 50-Ohm coax feedline?
They weren't originally designed for it, but I have seen applications that use bidirectional radio chips such as the TI CC1101 to pass control/status data in both directions through a coax alongside DC power and another RF signal.
The chip handles a lot of the details and is relatively easy to set up with a microcontroller. In fact, in one design, a very simple &quot;soft core&quot; microcontroller embedded in an FPGA takes care of it. The data rate can be set anywhere from 0.6 to 600 kbps.