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Network Video Technologies S E C U R I T Y I N D U S T R Y L E A D E R |
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Technical Bulletin |
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Comparison of Video Equalization Methods There are many UTP transmission methods available on the market today, resulting in confusion in the selection of a proper and well performing solution. Passive (non-amplified) Solutions These solutions consist of transformer-like devices that convert the un-balanced video signal to a balanced one that is suitable for transmission over UTP wire. There is a wide range of quality of these devices, with varying levels of interference immunity, transient protection, and reliability. Over the years, our customers have learned (sometimes at great expense) of the importance of a high quality device. That being said, virtually all passive devices on the market have negligible attenuation. It's the wire that limits our distance. NVT specifies its maximum wire distance at 750 feet (225 meters). This does NOT mean that the signal is lossless up to the specified distance, and then falls off rapidly. Rather, just like RG-59, the picture gets dimmer and grayer with distance. Some competitors may specify longer distances, but the same wire attenuation will produce the same results. Although NVT specifies 750 feet (225 meters) as our maximum distance, for excellent results we recommend shorter distances for higher-resolution cameras:
Please note that these distances are end-to-end and include any coax in the path. Passive-to-Active Solutions These solutions use a passive device at the camera and an active device at the receive end. That unit has gain to compensate for cable-loss. It also has a differential input, making the solution immune to ground-loops, and transient protection. There are three types of equalization methods: Dipswitch - NVT used to use this method long ago. The problem is that it affords only certain fixed gain settings while disallowing other desirable settings; Trimpots - NVT's single and 4-channel active devices use this ultra-stable method. It allows continuously variable adjustment to compensate for different wire gauges, categories, and lengths. Automatic Equalization - There are several products on the market that identify themselves as automatic. Some work over limited ranges, or require dipswitch range settings. We have yet to find one that doesn't have miserable performance above 1000 feet (300 meters). One problem with these solutions is the method by which the gain adjustments are made, often measuring the wrong portion of the signal. The last thing we need is for car headlights in a darkened parking lot to initiate changes in amplification. Another problem is frequency response. It does no good to compensate the DC gain if the high frequencies are out of adjustment. If mid-band frequencies are not respected, the result is right-shift "smearing." Finally, we have found that wide gain adjustment often comes with poor signal-to-noise (snowy video). Most manufacturers are unwilling to use more costly low-noise opamps. DigitalEQ™ The NV-872, NV-1672, and NV-3272 Active Receiver Distribution-Amplifier Hubs employ a four-band equalization method that ensures flat frequency response across the spectrum. The result is crisp clear video, allowing for the identification of license plate numbers, or faces, especially in darkened areas. The gain adjustment is continuous across all distances for each of the four frequency bands. The DigitalEQ™ detects signal polarity and will invert and correct a mis-wired ±30 Volt common-range input, ensuring a noise- and hum-bar free picture under ultra-hostile conditions. Finally, the DigitalEQ™ has at-a-glance per-channel LEDs, allowing immediate identification and diagnostics of functional, out-of-range, or faulty signals. Active-to-Active Solutions When required, this solution pre-amplifies the video, allowing extended-range video up to one mile (5,280 feet, 1.6km) when used with any NVT active transmitter. Active-to-Active Solutions When required, this solution pre-amplifies the video, allowing extended-range video up to one mile (5,280 feet, 1.6 Km) when used with any active NVT receiver. |
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