avvora posted a topic in System DesignI have installed three 4 channel systems with 4 cameras and all of them have had vertical lines scrolling across the screen horizontally. It is not present (or not noticeable) when just one camera is connected to the DVR, but once you start adding more cameras it gets worse. I feel like it must be a ground loop problem because even if one of the baluns touches any metal surface on the DVR the lines come back, you don't even have to connect the camera, just let the metal surface of the BNC connector touch clean metal anywhere on the DVR - Boom! Lines come back. I fixed it on one of the jobs by powering each camera with its own dedicated 12v plug in AC/DC adapter. However this did not fix the problem with today's install. I spent hours troubleshooting the problem. I even powered two of the cameras locally with its own 12v battery so no power was being sent over the cat5 at all. The lines still didn't go away! If there are four cameras connected to the DVR it's really bad but if you unplug the power source from any three out of the four cameras, the remaining camera will have a clean picture. All four cameras tested individually had a clean picture when connected by itself. It's got to be ground loop interence right? But if I install ground loop isolators, what type should I use and should they go on the camera side or the DVR side, or both? Also I see Hikvision makes an HD-TVI ground loop isolator that goes on the power wire, not the video. I wonder if I should but ground loop isolators on both the video and power...this could start getting expensive! This is frustrating because it's holding me up from getting paid on this particular job, but at the same time I'm interested to find the cause of this problem. The symtom was the same on all three systems, all using Cat5e and baluns. Any suggestions or similar experiences? Please share!