THE BLUE BOX LT MAKING UP CAT. 5 CABLE WITH RJ45 CONNECTORS 31
LCDBBMUCAT03Sept08
THE IMPORTANCE OF A PROPER CRIMP
Imperfections in a crimp adds a resistive and capacitive load
at that point in the network. For example, if the voltage is
dropped to 75% of its previous value at each crimp, the
signal voltage will drop from 5V to 3.75V on the first crimp
and 2.8V after the second.
Therefore, multiple bad crimps can cause the signal to be
lost in the noise threshold after consecutive voltage drops;
this loss of signal through the length of a cable is called
attenuation. Impedance is the measurement of cable
resistance to a signal, measured in ohms.
If the RJ45 connectors are improperly terminated, the
additional resistance and capacitance at the connector
changes the “character” of the wire causing what is called
an impedance mismatch.
Impedance mismatch causes signal attenuation because
part of the transmitted signal is reflected back much like
an echo and does not reach the receiver. Inconsistent
crimps compound these effects and cause a larger part of
the signal to be reflected back.
When these reflected signals collide with the first
discontinuity, part of the signal will return to the original
CABLE AND CRIMPING qUALITY
direction and create multiple echo effects. This results in
an “unstable bus” because these reflections or echoes
make it difficult for our devices to receive data.
Figure 1. 4 shows a daisy-chained network; if there are bad
crimps as described above the transmitted signal from the
relay panel can lose strength with every device.
TYPE OF WIRE
There are three types of wire that use RJ45 crimped
connectors. The first is a flat telephone cable, made of 26
gauge wires. It is not Cat. 5 since the wires all run parallel to
each other and are not twisted and thus lack immunity to
noise. We use this type cable for low frequency signals and
short distances, such as to provide power to the clock.
The other two cables are round in form. They come in
stranded and solid varieties. The stranded wires are used
for “patch cables” from a computer to a wall socket.
Figure 1.4
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