Ground Loop Explained
A ground loop occurs where there are two paths to ground over a section of cabling.  This can occur, for example in your case, where you have a ground shield on a coax cable.  If that ground shield were connected to a common ground between the two pieces of equipment (such as earth ground or some other shared ground at both ends of the cable), then there would be a potential ground loop due to multiple return paths from one end of the cable to the other and the resistance of the two paths is not the same.  There is also a potential for a ground loop problem if there is induced AC on the shared ground (this is often the source of hum on audio lines).



However, if the coax ground is not connected at the far end, or the equipment at the far end is not connected to a common ground point shared by both ends, then there is only one ground return path and no ground loop exists.  (However it is then possible to have a situation where you have no ground between the two pieces of equipment -- both paths are broken -- and your signal doesn't work as intended.)