EXFO CableSHARK P3, Руководство пользователя, Страница: 23 / 321

CableSHARK
P3
User Guide
11
Not all cables are the same, hence the variations in VOP. Conversely, not all local loops are the same.
Some local loops are longer than others and susceptibility to noisy environments varies. All signals on these
loops, regardless of cable length or environment, are subject to attenuation. Attenuation affects both
transmitted and reflected signals and, if the signal-to-noise ratio is low enough, impairments may not be
identifiable. To overcome the affects of attenuation, use a larger pulse width (more energy) to locate
impairments or take measure from both ends of the cable.
The following diagrams depict possible TDR traces and their causes.
Cursor position =
Marker position =
Cursor / Marker Delta =
0.0 1250.0 2500.0 5000.0 3750.0
ZOOM IN
VERT
MAIN
MENU
E F
CHG
-1.000
-0.750
-0.500
-0.250
0.000
0.250
0.500
0.750
1.000
1998.7
0
1998.7
Pulse Width: ft
ft
300 ns
ZOOM IN
HORIZ
SELECT
MARKER MORE
AUTO
REPEAT
Reflections at ft(dBRL): 1998.7 (33.8+)
Cursor position =
Press or to move cursor
The above figure depicts an OPEN circuit or a
high impedance fault. Depending upon the size of
the reflected pulse, the OPEN could be an partial
(small pulse) or complete (large pulse) open
circuit. Of course, the length of the cable,
attenuation on the line, and the size of the
outgoing pulse will play a big role in determining
the reflection.
0.0 1250.0 2500.0 5000.0 3750.0
ZOOM IN
VERT MAIN
MENU
E F
CHG
-1.000
-0.750
-0.500
-0.250
0.000
0.250
0.500
0.750
1.000
ZOOM IN
HORIZ SELECT
MARKER MORE
Reflections at ft(dBRL): 1998.7 (33.8+)
AUTO
REPEAT
Cursor position =
Marker position =
Cursor / Marker Delta =
1998.7
0
1998.7
Pulse Width: ft
ft
300 ns Cursor position =
Press or to move cursor
The above figure depicts a SHORT circuit or a
low impedance fault. Depending upon the size of
the reflected pulse, the SHORT could be an
partial (small pulse) or complete (large pulse)
short circuit. Of course, the length of the cable,
attenuation on the line, and the size of the
outgoing pulse will play a big role in determining
the reflection.