Extron electronics IN1404XT, Руководство пользователя

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Installation, cont’d
IN1404XT Video Scaler and Switcher • Installation 2-6
The Microtest OMNI SCANNER 2 performs comprehensive certification testing to
the proposed CAT 6 standards. Other manufacturers also make testing equipment.
The tests include advanced diagnostics for troubleshooting the cause and location
of many cable and termination problems. For simple installation testing, the
Microtest MICRO SCANNER PRO tests wire map and cable length, including
individual cable pair length.
Equalizing pair skew
The manufacturing process for network (CAT 5) UTP cable leads to a condition
called pair skew. For best results, pair skew needs to be equalized when using the
CAT 5 cable in A/V applications. The design of Extron’s skew-free A/V UTP cable
minimizes pair skew to the point that equalization is not required.
Skew exists between pairs when the physical length of one wire pair is different
from another. As the transmission cable length increases, the amount of skew
increases. Skew affects the displayed image when the differential length between
wire pairs exceeds 2 feet, causing the timing of the red, green, and blue video
signals to appear out of alignment (horizontal registration errors). A white vertical
line on a black field can appear as individual red, green, and blue lines that are
close together; the signal transmitted on the shortest wire pair leads the other colors
and appears to the left on the display.
UTP cable test equipment measures and reports wire pair length. The report on the
various pair lengths can be used in equalizing pair skew. The nominal velocity of
propagation (NVP — the speed at which the signal travels on the transmission line,
measured as a percentage of the speed of light) of TP cable is very close to that of
conventional coaxial cable. The similarity in NVP means that:
• by using an Extron IN9045-L6 15HD male-to-5 BNC male, 6’ cable, to adapt
the output on a 15HD connector to BNC connectors,
• and then adding an additional length of coax equal to the length of pair skew,
placed on the receiver’s output,
you can equalize the effects of pair skew (figure 2-6).
If UTP cable test measurement cannot be done, pair skew can still be equalized by
viewing a test pattern with a critical eye. Examine the test pattern for loss of
horizontal registration and, through a process of trial and error, equalize any pair
skew with coax extensions on the red, green, and/or blue outputs.
Extron skew compensation coax cables are available in lengths of 2 through 20 feet,
see Appendix A, Reference Information, for part numbers.