Kenrik Technology
The Kenrik Resources family of UTP Active Video Receivers uses carefully crafted compensation or “equalizers” to restore the severe video waveform degradation that occurs when passing through long runs of UTP cable. The equalizers are specifically tailored for the most popular and efficient type of UTP in use today, CAT5e.
Here is how it is done.
A Video Receiver Channel in this family of products has two major components: Differential UTP Video Receiver and Five Stage Video Equalizer.
Differential UTP Video Receiver
Video arriving on a long pair of CAT5e needs very careful processing to allow full recovery of the video waveform and rejection of all other noises added to the cable by the electromagnetic environment through which it passes. The active input electronics must accomplish this.
The input circuits consist of a very high performance wideband video differential amplifier that is optimized for video processing of UTP transmitted video sources. This amplifier has very high common mode rejection of the interfering signals that have been added to each wire in a UTP pair. The common mode rejection is broadband, covering the entire video frequency spectrum. The size of the common mode noise allowed is also considerable, up to at least 12 volts peak to peak. When the video leaves this amplifier stage, noise has been greatly suppressed and it can be presented to the Equalizer bank for proper restoration to nearly its original characteristics.
Five Stage Video Equalizer
Once the input video has been cleaned of common mode noise, it is presented to a bank of five equalizers. Only one equalizer will be selected to pass video to the Video Output BNC. The choice is made by an operator adjustment of the front panel COMP control. The operator judges video quality shown on a monitor or an oscilloscope as COMP is varied, choosing the setting giving the best-displayed image on the monitor or best video waveform display on the oscilloscope.
Each of the five equalizers has a frequency shaping network optimized for a range of length of CAT5e cable. For example, the number 5 equalizer, selected by turning COMP fully clockwise, corrects the video that has passed through approximately 2500 to 3000 feet of cable. Shorter lengths of cable fall into the ranges of the lower numbered equalizers. The recovered video waveform is quite good, with only small deviations from the ideal.
Equalizer correction takes care of both low frequency gain loss, due mainly to cable wire ohmic resistance, and high frequency losses due to wire skin effect and insulation losses. The goal is to give at the output, a video waveform that is correct in all its frequency dependent and time domain (step and pulse response) aspects as the original source video. This is most evident when test patterns such as Multburst and Pulse/Bar are used. Horizontal and vertical sync pulses, critical for reliable recording on DVRs, and proper display on monitors is guaranteed. Color subcarrier recovery is also very good, as the full video bandwidth is fully restored.
