Black Box ACU5011A, ACU5010A manual Troubleshooting, Reporting and Compensating for Video Skew

CHAPTER 7: Troubleshooting

7.2 Reporting and Compensating for Video Skew

If you notice that one or more of the primary colors (red, green, or blue) in the video image displayed on your monitor has separated from the others and is horizontally offset from them on your screen—for example, if colored shadows trail bright white objects, as shown in Figure 7-1—then your Extender system might be affected by video “skew.”

The delayed color usually appears as a vertical band on the right- hand edge of

the white object

Figure 7-1. Skew at its most visible (color trailing a white object against a

dark background).

The Extender works by transmitting the three primary video colors on three of the four wire pairs in a twisted-pair cable, as shown in the Appendix. These pairs are twisted differently from one another in order to prevent the signals on one pair from interfering with the signals on the other pairs. Over long distances, the pairs’ different twist ratios will actually cause the pairs to differ significantly in total length, with tightly wound pairs being longer than more loosely wound pairs. This is good for data transmission, but in an Extender system it will cause the three color signals to arrive at different times and to be displayed at different positions on the screen.

If this appears to be a problem in your system, there are several things you could do about it:

•Can you use a lower screen resolution? Lower resolutions produce less skew.

•Can you shorten the twisted-pair cabling distance between the Extender’s transmitter and receiver? Shorter cables cause less skew.

•Can you swap in a type or brand of cable with less extreme differences between the twist ratios of the wire pairs? Generally, the ratios in CAT5 cables are not as different as those in CAT5e cables, which in turn don’t differ as much as those in CAT6 cables, but the ratios will vary considerably depending on the manufacturer and make.

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