RESTORING PICTURE QUALITY ON CCTV SYSTEMS
RESTORING PICTURE QUALITY ON CCTV SYSTEMS
By: Frank McClatchie
The quality of a CCTV picture basically depends on the number of “lines” the camera can delineate and the number of “lines” the DVR can store and the number of “lines” the monitor can display. The component with the lowest “lines” capability thus sets the highest possible picture quality that can be observed “on the test bench”. The term “lines”, in this case, refers to the number of vertical lines that could be distinguished in a picture (thus, a measure of picture quality), not the number of scanning lines used in the system. All North American standard CCTV cameras use 525 scanning lines, but may have anywhere from 330 to 700 lines of resolution (equating to quality). The final limitation on picture quality then, is the Coaxial Cable (or twisted pairs) loss between the camera and the monitor. The cable loss in the transmission facility is the greatest factor in degrading overall CCTV quality, and therefore deserves close scrutiny when designing a CCTV system (note the table below).
Color brightness and picture quality degrades as the picture travels down a coaxial cable. This is caused by the resistive losses, capacity and inductance of the cable itself and varies with the specific type of cable being used. This reduction in picture quality becomes noticeable on RG-59/U cable in 200 to 300 feet and becomes very apparent in another 500 feet. After two or three thousand feet of coaxial cable, the color fades out to a black-and-white picture and the picture becomes very fuzzy. This problem can be reduced by using a higher quality (low loss) type of cable, but a far better solution is to eliminate the problem altogether by canceling the cable loss entirely with an automatic amplifier/equalizer such as the ACE472 at the receiving end of the system. The following table shows the number of feet that any given number of “lines” can be transmitted without noticeable degradation:
LINES RG59/U CAT-5 RG59/U with ACE472
330 686 Feet 289 Feet 5300 Feet
400 615 Feet 259 Feet 5200 Feet
470 585 Feet 246 Feet 5100 Feet
570 521 Feet 219 Feet 4900 Feet
700 470 Feet 198 Feet 4700 Feet
The ACE472 Automatic Cable Equalizer will restore the picture quality of a CCTV system by completely restoring all color and picture detail to the exact same quality that was produced by the camera. The better the Camera, DVR, and Monitor, the better the received picture will be. Once the ACE472 is in place, much higher picture quality can be obtained by up-grading the Camera, DVR, and Monitor to the desired quality level.
The picture brightness and frequency-response correction provided by the ACE472 is fully automatic and does not require any routine adjustments even when video switchers are used to switch from one camera to another. That means that all cameras and cables connected to the “CABLE ACE” will always have the same peak brightness and best possible picture clarity on every picture. When the ACE472 is connected at the receiving end of the system the distance to the camera is no longer a factor in CCTV picture quality.
CLICK HERE to see more about the ACE472
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