Ground Loop Problem?

[garethnboyd 0]

So I've got a 16ch DVR set up in a main office building. 5 cameras are installed on this building and function just fine. There are 3 cameras on 2 outlying structures located about 200ft from the main building that houses the DVR. I have RG-6 running the distance in an underground conduit. Whenever the 3 outlying cameras are connected to the DVR I get no video from them, but a lot of interference on the whole DVR(and a certain camera from the first 5 in particular). If I connect these cameras to a test monitor instead of the DVR(still using the distance cable runs in the main building) they seem to function fine. I installed ground loop isolators on the coax lines, but still don't get any video. Any ideas?

[garethnboyd 0]

So after getting my tech to reposition the ground loop isolator to the camera side instead of the DVR side, I now get video. The video is really warped though. Any chance the (lower end) ground loop isolator just isn't stripping off all of the transient voltage? What if I put two ground loop isolators on one line? Any ideas or suggestions are welcome.

[tomcctv 187]

Hi. RG6 is not the best for CCTV can you pull cat5 ??

 

also which end are you powering cameras from

[daveshoot 0]

I did used to see ground loops with analog cameras that required more than one isolator to resolve. You could borrow one from one of the other lines to add as a test.

[garethnboyd 0]

Power on the 3 outlying cameras is local to those cameras. I get distortion on the DVR even when no power is going to those cameras and the BNC is touching any metal on the back of the DVR. I will be on site tomorrow to try some things, so we'll see. Cat5 really isn't an option here. Why would it be better for just 200ft? I know it has some distance advantages over coax, but I wouldn't this run to give me any trouble.

 

Thanks for the input

[tesc_cctvpro 0]

You need to establish where the cable is earthing (if it is an earth and not other induced interference). placing at the dvr or at the camera is a hit and miss affair - find and eliminate the source of the 2nd earth. Test your cable to see what voltage if any is running in the coax shield. If the outside structure is metal, have you mounted the cameras directly to the metal structure? Ground loop isolators won"t help with severe ground loops>

 

Metal camera brackets mounted directly to a grounded metal structure, BNC making contact with some other grounded structure, perhaps a join in the cable making contact with a grounded component, perhaps cable damage in the conduit.

 

Up to 500ft coaxial will give you twice the signal level at the dvr than passive UTP. Mostly the viewer doesn't even know that he's missing 40% of the image content.

 

Since the distortion occurrs without the three cameras powered, there has to be voltage in the shield of one or more cameras connected to your DVR.