HOW TO AVOID INTERFERENCE ON CCTV?

HOW TO AVOID INTERFERENCE ON CCTV?

If you install a large number of CCTV video systems, you have probably experienced external interference from one or more sources. The most common interference that occurs with video surveillance systems is the 60-hertz power from the power sources, which normally resembles two or more black horizontal bars on the monitor screen.

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It is useful to know that the number of bars or lines of interference you can see on the screen is the interference frequency and this will help you to find the source of the problem.

An example is when dozens of vertical lines (usually white and irregular) are executed up and down the screen, moving on the screen or dancing in one place. This type of problem may appear in your video image when there is an interference frequency source in the low kilohertz range that crosses the coaxial cable or directly into the camera through the power supply.

The source of this error is usually an inverter (uninterrupted power supply UPS) used to power your cameras and DVR.

If the vertical lines around a point like the Hula shape, it is probably the interference signal comes from a blocked (60Hz synchronized) rectangular wave UPS which is usually purchased for computer backups.

These inverter units have actually set a square wave of 60 Hz AC instead of the normal 60 Hz sine wave that is obtained from a socket. The normal 60 Hz has single frequency energy, 60 Hz, which is easy to determine by the internal power controllers of the cameras. However, the square wave has all frequencies from 60 Hz to several hundred megahertz. The signal can not be effectively filtered by the internal camera controllers. For example, the 60 Hz square wave harmonic frequencies enter the camera through the power supply and pass directly through the controls to the video amplifiers where they are printed on the video signal itself.

If this is the case, try to turn off the UPS system and disconnect it completely to ensure that the square wave energy can not reach the camera by any means. Then turn on the camera by connecting it to a local power supply to see if the problem is there. When you do this, you know that you need to replace the square wave UPS with half-signed waves or a quasi-signed wave UPS.

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A rectangular inverter should never be used with analogue devices. Another form of high-frequency interference enables the video to see the image through a screen door with hundreds of lines forming a cross pattern of woven material both vertically and horizontally. This indicates a high-frequency variable in the hundreds of kilohertz range.

Common sources for these types of interference are AM radio sender and FM radio transmitters. The good news is that you have to be very close to the sending tower to have a problem.

A station that is one kilometre away will not be a problem, but one on the street can enter your system. If you have this type of interference, go and look around large antennas, especially in the building where your system is installed. If your video splits the base of a high-power transmitter, you will be hard pressed to get the irritating jamming signals out of the picture.

Eliminating this form of a high-frequency cross talk on a video cable or input to video amplifiers requires an extremely efficient high-frequency input equalization circuit to be effective. F M Systems input balancing systems are extremely effective in eliminating RF interference in a CCTV video image.

When you discover this type of interference, the solution is to place a common mode high-frequency balanced amplifier in the video path of the DVR. This product not only eliminates most of the high-frequency interference but also alters the image and locks the low-frequency ground loops.

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Please call us on 0333 006 4005 or email us at sales at cctvdvrsystem.co.uk for more information.