By: Don McClatchie


Many CCTV Closed Circuit TeleVision systems use a UPS Un-interruptible Power Supply to provide guaranteed continuous power to operate a surveillance system. The UPS also provides down stream voltage regulation that protects equipment in the event of under or over voltage swings that occur during “brown-outs” or brief power outages. The UPS will also protect equipment from voltage surges or spikes coming from the Main Power Line. Using a UPS to power your CCTV system is a good idea if you have a budget for it.


Have you ever had interference in your CCTV monitor that exhibited dozens of narrow vertical lines either black or white, and as thin as a pencil line. They may be staggered or jagged from the top of the screen to the bottom and may even dance side to side slightly while standing in one place or move across the screen slowly from side to side. If the lines stand still and dance around one spot your cameras are line locked, but if they slowly move across the screen then your cameras are not line locked. If you have this kind of interference on your monitor, there is a good chance that the system is being powered by a UPS and that the interference is coming directly from the UPS.


Some models of UPS Un-interruptible Power Supplies will induce interference into your CCTV picture. This interference can enter your CCTV system through the ground in the case of shared grounds like a ground loop or directly through the power supply used to power the camera. Technically UPS power supplies come in two output types. The most common kind is the low cost square-wave output type, like the kind used for computers and sold in computer stores, the second less common kind is the sine-wave, simi-sine-wave or quasi-sine-wave type used to power analog equipment.

The word “sine-wave” refers to the output waveform being sinusoidal in the shape. A pure sine-wave has only one frequency, and in the case of line voltage that frequency is 60Hertz or (60 cycles per second). The output of this type is well filtered to remove all other frequencies that might interfere with the equipment it is powering.

The “square-wave” type of UPS will put out the same 60Hertz frequency but its output waveform is that of a square-wave. A 60Hertz square-wave signal contains the “fundamental” or lowest frequency of 60Hertz, however it also has every “harmonic” or multiple of that frequency all the way up to and beyond the video frequency range. Strong high level signals in the Kilo-Hertz region (1000Hz) and even in the Mega-Hertz region (1000,000Hertz) will interfere directly with video. These interfering signals are multiples of 60 Hertz and are locked to the line rate which makes the interference stand still on the screen if your cameras are line locked. If not line locked the interference will slowly move across the screen.


One way that the interfering signal can get into the CCTV system is from a power supply. If a square-wave type UPS is used to power the camera, the high frequency interfering signals can enter through the AC or DC power supply and become part of the video by cross-talking directly to the video amplifiers in the camera. The high frequency interference will get through the cameras power regulators because the camera was designed to filter out 60Hz AC, not hundreds of Kilohertz of AC. DC powered camera’s can have the same problem for the same reason, however the interfering signal will always be moving on the screen because DC cameras cannot be line locked.


Another way interfering signals can enter the video is through an induced ground loop. The UPS is grounded and if the camera is also grounded some of the UPS energy can flow down the coax cable to the cameras ground. This sharing of grounds will induce the interfering signal onto the video. A ground at the camera can be a tricky thing. If you are using a DC powered camera, the coax cable shield and the negative power supply wire are the same at the camera. This means that if the negative power supply is grounded anywhere, then your camera coax shield is also grounded at that point and it can induce a ground loop.

If you are using a common power supply to power multiple cameras and even one camera is grounded then the ground connection will back up to all of the cameras. Common power supplies for DC cameras are especially susceptible to this problem. The common power supply ground loop may not affect all the cameras depending on the distance of coax and the grounding conditions at each camera.


To begin trouble shooting you must first identify the source of the interference. First disconnect the suspected UPS and turn it off (power it down). This will guarantee that the UPS cannot create the interference in the first place. Then reconnect the equipment that was powered by the UPS to a normal non UPS power line. Check the monitor and see if the interference has been eliminated. This test will check for direct camera power supply and ground loop type interference at the same time.

If your interference did not go away and you suspect that another UPS somewhere else in the building is operating, you can check for ground loop interference by placing a battery operated monitor on the end of the coax cable at the DVR end of the system. Observe the monitor. If the interference is gone, that indicates ground loop interference. Confirm this by touching the original DVR ground to the connector shield on your battery operated monitor while you are watching the picture. Use a short wire or a coax jumper (shield only). If you touch the ground to the monitor the interfering signal will re-appear if it is ground loop induced interference.


If the interference is resolved by disconnecting the UPS then you should replace the UPS with a sine-wave, simi-sine-wave or quasi-sine-wave type of UPS. The best way is not to create the interfering signal in the first place. If the interfering signal is getting in through a ground loop then isolate the cameras from ground at the camera end. This may be more difficult when using common power supplies however first try an isolated wall mount power supply on one camera to test whether power supply isolation will resolve the problem.


If you cannot isolate the problem and resolve the interference then please contact me at: 800-235-6960 my name is Don McClatchie and I would like to talk to you about your specific problem. Together we can find the solution to your problem.