Extron Electronics VTR001 User Guide - Manual (Page 14)

Equalizing Pair Skew
Pair skew issues are eliminated when you use Extron Skew-Free AV 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 AV applications. The design of the Extron Skew-Free AV 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 coaxial cable 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:
• Switch to the Extron Enhanced Skew-Free AV UTP cable.
• Add a skew compensation cable equal to the length of pair skew to the output of the
receiver.
• Install an Extron Skew Equalizer, SEQ 100 15HD (part number: 60-676-01), on the
video output of the receiver and adjust the skew for the leading video image.
Sharpness Adjustment
The longer the cable being used, the greater the signal loss. The image sharpness may
be enhanced by turning a peaking adjustment screw located on the top of the receiver.
Increased peaking can compensate for detail (mid- and high-frequency) loss from low
bandwidth system components or capacitance in long cables. Adjust this control using the
included adjustment tool while viewing the displayed image to obtain the optimum picture
sharpness. Turning the control clockwise increases peaking and turning it counterclockwise
decreases peaking.
OUTPUT
VT R0 01 M AA P
SHARP
Sharpness
VTT001 and VTR001 User Guide • Installation 9