CS 3432 Lab 3.
Measure, using floor tiles, and cut a 100ft. length of Category 5 Unshielded Twisted Pair
(Cat 5 UTP) cable. This Cable is used for Local Area Networks (LANs) and consists of 4 pairs of
wires, each of which have been twisted together to improve noise rejection. You will be using two
pairs in this lab.
1. Carefully cut back a about two inches of the outer blue jacket from each end of the cable.
Notice the color coding scheme of the wires. There will be blue, green, orange and brown
pairs, with one of each pair having more white (or even being all white). Carefully strip about
3/4 inch of the insulation from the Orange and Brown pairs on both ends. On one end (End A),
join the Orange wire to the brown wire and the two whites to each other by twisting them into
a double helix.
On the other end (End B) connect the Orange wire to the clock output on the breadboard
and its white wire to ground. For now, leave the brown wire and its white wire disconnected.
Connect an Oscilloscope probe to End A with the ground to the white wire and the probe
tip on the junction of the orange brown wires.
Figure 1.Initial setup
2. Drive the wire with a 100KHz signal. Observe and record the wave form. (If the waveform is
unusable because of noise, try making a differential measurement using two scope probes and
subtracting.) Explain what’s happening. Think about the speed of the signal as it travels along
the pairs.
3. Next connect the brown wire to its white partner. Repeat the measurements. Explain what’s
happening.
4. Now connect the brown wire and its partner to the 1k ohm potentiometer (variable resistor).
Since this is a three terminal device, leave one of the end connections open. Turn the knob of
the potentiometer to observe its effects on the waveform. Explain what’s happening. At the
point where the waveform looks the best, disconnect the cable and measure the resistance
using a hand held meter.
5. What is the characteristic impedance of the cat 5 cable?
100 ft. 100 ft.