ideal
= no
losses
Seneca College - School of Electronics and Computer Engineering - C. Rodgers
DCM555 - Data Communications
Practice Exercise 2 - Transmission Lines
(Note: Show all calculations, express your answers to an appropriate number of significant digits (at least three) and
use the correct units in your answer. Place your answer in the space provided.)
1.
An ideal transmission line exhibits the following Time Domain Reflectometer (TDR) waveform. Find
the terminating load resistance and the length of the line if the velocity factor is 76%:
4 div X 0.2 s/div = 0.8 s
4 div
v=d/t
d= vt/2
factor of 2
from round
trip
d = (0.76)(3 X 108) (0.8 s) / 2
0.2V/div
= 91.2 m
0.2µs/div
Reflected pulse is In Phase and equal to incident pulse (since ideal)
Therefore, ZL = Open
ideal
= no
losses
2.
ZL = ____________________
91.2 m
l = ____________________
An ideal 270m transmission line is terminated in a short circuit. Complete the TDR waveform below
if the velocity factor of the line is 60%.
v=d/t
t = 2d / v
t = 2 (270m) / (0.6)(3 X 108)
= 3 s
# of div = 3 s / 0.5 s/div
6 div
= 6 div
100mV/div
Reflected pulse is Out of Phase and
equal to incident pulse (since ideal)
500ns/div
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Seneca College - School of Electronics and Computer Engineering - C. Rodgers
3.
Below is the TDR waveform for an ideal 50Ω transmission line with a velocity factor of 80%. Find
the length of the line and determine what you can about the termination load.
t = 5.4 div (5 s / div)
= 27 s
5.4 div
d= vt/2
d = (0.8)(3 X 108) (27 s) / 2
= 3240 m
= 3.24 km
Reflected pulse is Out of Phase and
smaller than incident pulse
2V/div
Therefore, 0 < ZL < ZO
5µs/div
NOTE: Tx line is ideal, so no losses are associated
with the Tx line itself. However, the mismatched
load results in only a partial reflection, the rest is
absorbed by the load
4.
3.24 km
l = ____________________
0 < ZL < ZO
ZL = ____________________
Below is the TDR waveform for an ideal 50Ω transmission line with a velocity factor of 55%. Find
the length of the line and determine what you can about the termination load.
t = 4.5 div (1 s / div)
= 4.5 s
d= vt/2
d = (0.55)(3 X 108) (4.5 s) / 2
= 371.3
Reflected pulse is In Phase and
smaller than incident pulse
4.5 div
Therefore, ZO < ZL <
0.5V/div
1µs/div
NOTE: As in 3 above, the partial reflection results
from some of the pulse being absorbed by the
load, the rest being reflected.
371m
l = ____________________
Z <Z <
O
L
ZL = ____________________
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