Video Ground Loop Puzzle

Hi everyone.

I posted not too long ago some issues I was encountering at a local horse ranch in Scottsdale AZ. As it turned out, there was a bad gound in the electrical system that kept damaging a number of cameras. The electric company sent someone and found the issue which now appears to be fixed.

So I went ahead a re-installed new cameras and everything has been working fine since.

Except for one thing: a few cameras are exhibiting some significant ground loop video issue, and specifically 2 of them. So I was wondering if I could get some suggestions on how to resolve this in the most expedient and economical way (the usual here).

Here's the set up: this was an exisiting system that I have serviced and added cameras to for the last 2 years. 24 cameras, all analog, 2 DVR's (IC Realtime), a mix of RG59/18-2 and CAT5 wiring. A mix of 12VDC and 24VAC power supplies. Power supplies are not centrally located (a few were placed closer to some stalls and buildings).

The main issue: 2 cameras, sharing the same 24VAC ower supply located in the DVR room.

I have isolated the cameras from the metal structures they were mounted on which helped a bit but the rolling bars are still there. I tried lifting the ground of the DVR's and other power supplies located in the same room with no success ( which puzzled me). The wiring (16/2?) and CAT5 goes to a junction box and then is split into 2 different conduits to reach the camera locations.

The one thing I have discovered when troubleshooting is that if I disconnect any one of the 2 cameras in question from the DVR (bnc balun), the ground loop completely disappears on the remaining connected camera.

I appreciate any suggestion on the issue.

Thanks.

Alan

PS: The secondary issue involves 2 cameras sharing a local 12VDC power supply, CAT5 for the video. The video noise is intermittent, not fixed by lifting the ground on the power supply. I have not isolated the cameras from the metal square poles on which they are mounted (poles that are integrated into the property metal fence). This is less critical at this time since the issue is intermittent but I will get to it next.

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