Operating Instructions
1–18
1502C MTDR Service Manual
The series resistance of the cable to the point at the cursor affects the accuracy of
the impedance measurement directly. In a cable with no large impedance changes,
the series resistance is added to the reading. For example, the near end of a long 50
W
coaxial cable might read 51.5
W
, but increase to 57.5
W
several hundred feet along
the cable. The 6
W
difference is due to the series resistance of the cable, not to a
change in the actual impedance of the cable.
Another limitation to the ohms-at-cursor function is that energy is lost going both
directions through a fault. This will cause readings of points farther down the cable
to be less accurate than points nearer to the instrument.
In general, it is not wise to try to make absolute measurements past faults because
the larger the fault, the less accurate those measurements will be. Although they do
not appear as faults, resistive pads (often used to match cable impedances) also
affect measurements this way.
When pushed, the VIEW INPUT button displays the input at the front panel CABLE
connector. When VIEW INPUT is turned off and no other buttons are pushed, the
display will not have a waveform on it (see Figure 1–16). The default condition
when the instrument is powered up is to have VIEW INPUT on.
O
F
F
O
F
F
O
F
F
ac 0.000 ft
O
F
F
Figure 1–16: Display with VIEW INPUT Turned Off
When pushed, the STORE button puts the current waveform being displayed into
memory. If already stored, pushing STORE again will erase the stored waveform.
The front panel control settings and the menu-accessed settings are also stored. They
are accessed under View Stored Waveform Settings in the first level of the menu.
Using VIEW INPUT
How to Store the
Waveform
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