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May 18, 2013
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I have a question about image quality during night in IR mode. This is on the 8 Channel Ultimate Series H.264 D1 Realtime Security DVR using 700TVL Indoor/Outdoor Vandal Resistant Dome Security Camera . The cameras are connected to the DVR with cat5e cable and Single Channel Passive Video Balun with Video and Power . The images during the day are great. The images during night in IR mode are great except for some horizontal lines that rise from bottom to top. Three of the four cameras have the lines , one does not. They are powered by 8 Channel Output Switching Power Supply . This is on a residential home.
Thank You,
Perry Walters
November 21, 2012
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How long are your wire runs? What kind of baluns are you using? I'd be willing to bet your cameras are starting to starve for power.
May 18, 2013
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The wire runs are about 60 - 70 ft. the baluns are single channel passive with video and power they use the plug on the end of cat5 cable. Here is the link to the baluns. https://www.securitycameraking.....-prd1.html
On the 3 cables that you are experiencing the horizontal lines at night, are they ran over any higher voltage cables? Because with Cat5 cable, it is an unshielded cable, which will pick up interference faster than a shielded cable. Also, have you tried disconnecting a camera or 2 to see if it goes away on the other cameras? If it is happening on only some of the cameras and not all, then we need to isolate potential causes. Have you tried taking the camera/s down making a new cable and tried to see if you can duplicate the problem? You can always try one of these to help clean the image https://www.securitycameraking.....-prd1.html . We have a balun version, but I figure since you already have the RJ45 ends on the cable this is the easiest solution to try. These get put on the end at the DVR to isolate noise from the video feed.
May 18, 2013
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Thanks for the suggestions.
I ended up purchasing a power supply for each camera and that solved the problem.
Would you suggest in the future to have a separate power supply for each camera ? The power supply with multiple
ends on it sure is convenient but if it causes the ground loop interference then it's not good to use.
November 21, 2012
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It just depends on the scenario. It sounds like in this case you may have had an Ohms load issue with other devices on the circuit. Power conditioners are always recommended, but they're pricey. Honestly, every scenario is different and Murphy's Law states that the moment I tell you independent power supplies are the way to go, you'll start running into the situation where they cause problems. 
March 16, 2014
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Once I was able to solve this by grounding the negative of the multi-camera power supply to the DVR chassis. Another time I had to switch to one supply per camera (1A supplies are a dime a dozen, eh?). The problem is the camera connects signal ground to power ground, and your baluns do not block DC. It's always a ground loop. Always!! Just sometimes you get away with it. So since the signals are connected at the DVR, the power supplies must float or you must have DC-isolating baluns (good luck with that). My system stumped several professional installers who claimed never to have seen the problem, but I think it's actually quite common. My "video hum" was worst at dusk and dawn as the IRs were powering up and down... probably by switching at different duty cycles.
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