User guide

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.
OUTPUT
VTR0 01 MAAP
SHARP
Sharpness
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 A/V UTP cable.
• Add a skew compensation cable equal to the length of pair skew to the receiver’s
output.
• 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 (Extron part number: 100-014-01LF) while viewing the displayed
image to obtain the optimum picture sharpness. Turning the control clockwise increases
peaking and turning it counterclockwise decreases peaking.
VTT001 and VTR001 User Guide • Installation 9