Extron electronic Twisted Pair Receiver VTR001 - Manual (Page 20)

VTT001 and VTR001 • Installation
Installation, cont’d
2-8
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
Pair skew issues are eliminated when you use Extron
Skew-Free
™ A/V UTP cables.
The manufacturing process for CAT 5e or CAT 6 network UTP
cable leads to a condition called pair skew. For best results, pair
skew needs to be equalized when using the CAT 5e or CAT 6
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 two 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 difference in NVP means that an additional length of
coax equal to the length of pair skew, placed on the receiver’s
output, equalizes the effects of pair skew.
CAT 5 TP cable can lead to registration errors between the red,
green, and blue video signals. Pair skew can be measured with
test equipment or identified by viewing a crosshatch test pattern
closely to determine if either the red, green, or blue video image
leads (appears to the left of) the other two video images. These
images can be minimized or eliminated by one of the following
methods: