Equalizing Pair Skew; Output Cabling; Computer Video - Extron electronics CAT 5 User Manual

Installation and Operation, cont'd
wire map and cable length, including individual cable pair
length.

Equalizing pair skew

The manufacturing process for UTP cable leads to a condition
called pair skew. 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) is very close to that of conventional coaxial cable. The
similarity 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 (figure 2-4).
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.

Output cabling

Computer video

The CAT 5 R BNC AV and the CAT 5 R BNC AV receive and
output RGB video. These receivers can also receive component
video, S-video, or composite video and output them on the R,
G, and B BNCs.
Reception of component video, S-video, or composite video
requires that internal jumper be reconfigured. See Jumpers in
this chapter.
2-6 CAT 5 Receivers • Installation and Operation
CAT 5 T 15HD A
AU
DI O
CO
MP
UT
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IFT
Audio NI TO
R
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T 5
T 1
5 H
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PC Computer
CAT 5 UTP Cable
Pair RGB video
... THEN insert a three foot
extension cable to equalize
1, 2 Red
UTP skew for red video.
4, 5 Green
7, 8 Blue
Figure 2-4 — Pair skew equalization
RGB Output BNCs — Connect the desired video output device
3
to the rear panel output BNCs:
For RGBHV video, use the R, G, B, H/HV, and V BNCs.
R G B
For RGBS video, use the R, G, B, and H/HV BNCs.
R G B
For RGsB or component video, use the R (R-Y), G (Y), and B
(B-Y) BNCs.
R G B
For S-video, use the R and B BNCs.
R G B
For composite video, use the R, G, and/or B BNC.
CAT 5 Receivers • Installation and Operation
IF cable measurement
indicates that the pair
with wires 1 and 2 is
three feet shorter than
the other signals...
R
PO WE DC
15V .5A
R
D IO B
AU L
A
L
R
V
CAT 5 R BNC A
V U T
H /H
O U TP
B
R G
B
G
R
T
IN PU
R G B
LCD Projector
H/HV V
H/HV V
H/HV V
H/HV V
2-7