Operating Instructions
1502C MTDR Service Manual
1–15
O
F
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O
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F
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O
N
ac 452.000 ft
Short
Figure 1–12: 455-ft Cable
A “rise” or “fall” is a signature of an impedance mismatch (fault). A dramatic rise
in the pulse indicates and open. A dramatic lowering of the pulse indicates a short.
Variations, such as inductive and capacitive effects on the cable, will appears as
bumps and dips in the waveform. Capacitive faults appear as a lowering of the pulse
(e.g., water in the cable). Inductive faults appear as a rising of the pulse (e.g., fray).
Whenever an abnormality is found, set the cursor at the beginning of the fault and
read the distance to the fault on the distance window of the LCD.
The reflection coefficient is a measure of the impedance change at a point in the
cable. It is the ratio of the signal reflected back from a point, divided by the signal
going into that point. It is designated by the Greek letter
r
and is written in this
manual as rho. The 1502C measures the reflection coefficient in millirho
(thousandths of a rho).
To measure a reflection, adjust VERT SCALE to make the reflection one division
high. Read the reflection coefficient directly off the display above the VERT
SCALE control. For reflections that are greater than 500 m
r
/div, adjust VERT
SCALE for a reflection that is two divisions high and multiply the VERT SCALE
reading by two.
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N
ac 0.000 ft
Figure 1–13: Reflection Adjusted to One Division in Height
Reflection Coefficient
Measurements
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