This is about a ground loop problem that I should have anticipated but I did not so there.
A camera is mounted on a crawler and the video feed goes through a 400 ft cable. Power to the camera is supplied through this same cable (the power from the cable supplies a dc-dc with 24v output whose ground I shall call crawler ground). When the motors on the crawler run there is a difference of almost 3 volts from crawler ground to power source ground. I thought of using a diff amp mounted on the crawler to produce a current loop and a diff amp where the power source is (where the video signal gets processed). Maybe a transformer for the video signal would work. I have 2 wires available through the cable for the video. I also have 2 wires available for communication to the crawler micro and I can see that is going to be another problem. If anyone can suggest a practical way to deal with this it would be greatly appreciated.