I'd like only use one cable to my security cameras. They require either 9 or 12 volts and send an RF signal back. At the moment I use precut lengths of cable from Henrys or other sites that have the power connector and a BNC connector at each end. But they are fixed lengths and not that easy to feed through conduit etc.
I'd like to feed the 12v down the RG58 as well as the RF. I think that should be possible with care as this is how mast-head TV amplifiers are powered.
I think I should put capacitors at each end to isolate the RF from the low voltage but I'm not sure what values etc.