3) Hills and valleys in the waveform, these can show bends, kinks, frays and water in the applicable cable.
(e)
If you see a failure condition in the applicable cable, turn the <>POSITION control.
(f)
Put the cursor on the leading edge of the rising or falling pulse.
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MAINTENANCE MANUAL
TEST PULSE
RISE IN IMPEDANCE CAUSED
LEAVING TDR REFLECTED
BY FRONT PANEL CONNECTOR
PULSE
SEE
O F F
O
N
O F F
O F F
O F F
O N
O F F
O F F
O F F
O
USUAL CABLE CONDITIONS
Time Domain Reflectometer Displays
Figure 202 (Sheet 1)
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MAINTENANCE MANUAL
SHORT
ac 20.000 ft
O
N
O F F
O F F
O F F
SHORTED CABLE
OPEN
ac 20.000 ft
O
N
O F F
O F F
O F F
CUT CABLE
EXAMPLES OF CABLE FAILURE CONDITIONS
Time Domain Reflectometer Displays
Figure 202 (Sheet 2)
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MAINTENANCE MANUAL
POSITIVE IMPEDANCE
ac 20.000 ft
O F F
O F F
O F F
O F F
FRAYED CABLE
NEGATIVE IMPEDANCE
ac 20.000 ft
O F F
O F F
O F F
O F F
CRIMPED CABLE
EXAMPLES OF CABLE FAILURE CONDITIONS
Time Domain Reflectometer Displays
Figure 202 (Sheet 3)
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(g) Read the distance in the top right corner of the LCD.
NOTE: This value is the distance from the start of the
____ applicable cable to the cause of the failure.
(h)
If you do not use a 50 ohm terminator, you will see an open circuit at the end of the applicable cable.
(i)
Make a note of the distance to the open circuit. 1) Use a jumper to cause a short circuit on the other end of
the applicable cable. 2) Examine the waveform shown on the LCD. 3) Make sure the waveform now shows a short circuit where the
open circuit was.
NOTE: The length of the applicable cable is the distance
____
shown on the LCD.
4) If the waveform continues to show an open circuit at the same distance from the TDR, this is a failure.
NOTE: The distance to the open is the distance to the
____
failure.
S 972-013
(3) Measure the reflection coefficient:
NOTE: The reflection coefficient (p) is a measure of the impedance
____ change at a point in the applicable cable. It is used to find if the failure condition is important or not.
(a)
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