Black Box ACU5010A, ACU5011A manual Technical Note

SERVSWITCH™ WIZARD EXTENDER

The first section of the report indicates the length differences between the twisted pairs that are carrying the red, green, and blue color signals. One of the colors will have a reported length difference of “+0.0M”; this is the color carried by the shortest twisted pair. The other reported differences are how much longer the other pairs are than the shortest one.

TECHNICAL NOTE

Each meter of the length differences between the pairs that the Extender reports is equivalent to 5 nanoseconds of delay. For comparison, you can get a rough estimate of your system’s on-screen “pixel time” by multiplying the horizontal pixels by the vertical pixels by the refresh rate and then dividing 1 by the result. If the delay time is greater than the pixel time, color split will be noticeable.

For example, if the maximum reported difference is 1.5 meters, the delay between color signals will be 1.5 x 5 ns = 7.5 ns. If the screen resolution being used is 1024 x 768 x 75 Hz, the pixel time is roughly

1 / (1024 x 768 x 75) = 16.9 ns. Consequently, the color split will be less than half a pixel time and so is unlikely to be noticeable.

The second section of the report indicates which of the Skew Compensator’s top-panel switches should be set to ON to compensate for the twisted-pair length differences indicated by the report. All other switches should be OFF. You will see that each of these switches is constructed using 4 individual sliders. To set a switch to ON, all four sliders must be moved to the ON position. To set a switch to OFF, all four sliders must be moved to the OFF position. The example skew report on the previous page indicates that switches A3 and B4 should be ON and all the other switches should be OFF.

To compensate for the skew, set the Skew Compensator’s switches as indicated in the report and use a second cable to insert it into the twisted-pair cable run between the transmitter and receiver, as shown in Figure 7-2. If this is a lower- quality patch cable, it should be as short as possible. It doesn’t matter which cable you plug into which of the Compensator’s two RJ-45 jacks; the Compensator is fully bidirectional.

NOTE

Because the cabling between the CPU and the transmitter can itself introduce some signal skew, sometimes setting the Skew Compensator manually, by trial and error, produces better results than relying on the skew report. For any given wire pair (color), switches 1 and 2 each introduce a 10-nanosecond delay, switch 3 introduces a 5-nanosecond delay, and switch 4 introduces a 2.5-nanosecond delay. For more information, refer to the Skew Compensator’s manual.

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