I have designed many years a VGA cable based video camera cable which could hande video in two directions (from camera to mixer and return video to cameraman), a two-way voice connection (ClearCom type) and 12V power to the camera. All the signals run along an equally long (tens of meters) VGA cable. These were used years ago in various multi-camera productions at various events, for example to produce an image on the big screen of concerts. Was used by at least Procam Tuotanto a long time ago.
Here are some pictures of a prototype:
To get the idea of the signals what go on the VGA cable normally, take a look at this:
In good quality VGA cable at least RGB signals are small coaxial cables. The HSYNC andf VSYNC could be coax or just wires.
Other ID and control signals just go through as thin wires on the cable.
The signals were arranged to VGA cable so that the video signals were carried over R and G signal coaxial cables. The audio communications uses B coaxial cable for audio and one other “free” wire for it’s power.
All the remaining wires were reserved for camera power feeding so that several wires in parallel were used and + and -. A floating 24-30V DC (current limited to less than two amps max) was fed to the power feeding wires. On the camera end the power goes to a Mascot voltage 24V to 12V linear regulator module that converts to 12V DC that is right voltage to power many video production cameras. This arrangement allowed stable voltage to camera and the many volts of loss (load current dependent) in cable does not affect the output voltage to camera. Because the power – gets connected to video signal ground only at camera end (the power supply is floating on sending end), the noise caused by power feeding voltage drop on the cable does not affect the video signals.