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Hi all I have come across this for the first time in my five years of cctv installations. Here is the set up; 4 cameras (TVI - from GTec) TVI DVR from same company Coaxial Cabling (shotgun) Cameras powered with a 5A compact (adapter) power supply at the destination (i.e. same place where the DVR is located) Location of DVR and where all the cabling lives; in the loft of a bunglow. Output is completely teary and full of interference; see picture attached. Now I have been in contact with the supplier and they have advised us to carry out few tests and none of them seem to have worked so far: 1. At some places our coax cables were first running along the 220V electricals which the company thought was the major cause of interference. To remedy that we re-routed the wiring, i.e. made sure that it is 'completely' away from the 220s, and the closest we have ever got to a 220v with our cables runs is half a feet. Unfortunately the result is the same level of interference. 2. They asked us if by powering up the cameras individually using separate power supplies will fix the issue but using individual power supplies doesn't ever power up the cams. 3. We see output on the screen only in the case when ALL FOUR cameras are connected to 1 to 4 way connector lead. if you disconnect one or two from the lead then all the others do not show any video output 3.1 Also tried the boxed 10A power supply, same issue persists! 4. One of the 4 cameras doesn't even switch on, it comes on briefly for a second and then goes. This cam is the farthest away from the DVR 15 meters i suppose. 5. Now this is the reason I think it is a ground loop issue; I can feel a tingle on the BNC connectors at the back of the DVR when i touch them and of high intensity. 6. So keeping the above point in mind I decided to order some humblocks from systemQ, http://www.systemq.com/cgi-bin/commerce.exe?preadd=action&key=CON700 connected all of them up but there is NO video output when they are connected ( The sales guy at systemQ clearly said that these will work with TVI cameras, is there a compatibility issue here? My back up plan is to switch to analogue cameras and then use the humblock with them. Really do not have any other ideas, can anybody suggest anything please? ( Thanks Fahad