Specifications

TECH CORNER
22 ExtroNews 11.2 May/June 2000
-DISADVANTAGES
A transmitter and receiver are required— Transmission of video over
CAT 5 requires both a transmitter and a receiver for each signal. Both
units require power, and are considerably more costly than the cable itself.
Performance variations—Compared to coax, CAT 5 impedance is
much less controlled. Because of this, cable bends can change the
performance of the system. Two cables of the same length will likely
have a different overall bandwidth. This could result in each color
having a different level of sharpness.
Length variations—Say you cut a 500 foot section of CAT 5. The various
twisted pairs should all have the same length, right? Wrong. There can be
significant length variations between the twisted pairs. If you use this
cable to run red, green, and blue the time delay variations could cause the
image to look unconverged, even on a LCD, DLP, or plasma display.
CAT 5 uses the same connector as computer cable—This makes it
relatively easy to confuse the computer and video connectors. If you
plug an A/V CAT 5 cable into a plug for Ethernet, it is very likely that
you will damage either the A/V hardware or the computer system.
CAT 5 requires special handling—Sharp bends or even semi-sharp
bends can degrade system performance. For instance, a cable bend
around a 3" diameter will increase near end crosstalk (NEXT) by 1.9 dB.
A bend around a 1" diameter will cause NEXT to increase by 2.1 dB.
This is not a problem with coax cable.
No standards—CAT 5 equipment is not standardized. Because of this
you cannot intermix various manufacturers’ equipment.
A CAT 5 system is easily degraded—The figure below shows a CAT
5 system where a computer is attached to a CAT 5 transmitter. As
indicated in the figure the cable between the CAT 5 transmitter and the
wall plate is a weak spot. Substitution of a non-CAT 5 cable can degrade
the system considerably. For instance, if a 2' length of CAT 3 quality cable
is substituted for a 2' length of CAT 5, the near end crosstalk (NEXT*) will
increase by 8.0 dB.
+ADVANTAGES
CAT 5 is easy to install—Because CAT 5 is so small, it is easy to install
and easy to pull. The small size allows multiple CAT 5 cables to be run
in even small sized conduit. It is also quite lightweight so running many
cables doesn't present weight problems for the cable trays and
supporting structures.
Low cable cost—CAT 5 is inexpensive, not only in initial cost, but also
in terms of installing and terminating. This can be a big advantage in
certain situations. Imagine doing a staging event or a trade show
booth. When it's time to strike, just pack up the electronics and leave
the cable, wasting no time tearing cable out from structures, walls, or
under carpet.
Parts are easy to find—CAT 5 can be installed/terminated with parts
found at most any electronics store.
CAT 5 may already be there—Many places, such as universities,
already have CAT 5 installed.
Small connector size—Since CAT 5 connectors are so small, CAT 5
products can be made a fraction of the size of standard video products.
Some CAT 5 equipment is less likely to have ground loop
problems—
Some manufacturers’ CAT 5 equipment will be less
susceptible to ground loop problems. This is dependent on the
particular design.
RGB INPUT
RGB OUTPUT
RGBH/HVV
A
A-V AUDIO
L
R
B
ISOG C SYNC
Computer
Non-CAT 5 cable can
degrade signal quality
VGA Cable
CAT 5 Cable
BNC Cable
Projector
CAT 5 T 15HD A
H-SHIFT
BUFFEREDCOMPUTER
INPUT
AUDIO
ID PIN 4 ID PIN 11
LOCAL MONITOR
CAT 5 (cont.)