Operating Instructions
Ohms-at-cursor
The CT100 also displays the impedance in Ohms (Ω) at the cursor position. A reading before
and after a reflection from a fault shows the impedance mismatch that could cause such a
reflection.
Impedance measurements at the first fault in a cable are more accurate than impedance
measurements at more distant faults.
VSWR
VSWR is voltage standing wave ratio. VSWR measures the ratio of the maximum-over-time
amplitude of the nodes and anti-nodes of the standing wave off of a reflection. If there's no
reflection, VSWR will be 1. If all energy is reflected, VSWR goes to infinity. VSWR is a
unitless, scalar value.
The CT100 displays two different VSWR values. The first, labeled VSWR on-screen, will be
calculated from the total reflection relative to the output impedance of the CT100 (50 Ohms).
The second, labeled RVSWR, will be calculated from the reflection between the two cursors.
In other words, VSWR is based on the millirho reflection coefficient, while RVSWR is based on
the RRC, relative reflection coefficient calculation.
VSWR and RVSWR have a menu option to toggle the display of the values on-screen in the
Display menu.
Relative distance measurements
The CT100 displays the absolute distance from cable start and also the relative distance from
the passive cursor to the active cursor.
Note that Vp must be set accurately for the section of cable between the cursors for the CT100
to measure relative distance accurately. The pulse velocity of any part of the cable that is not
between the cursors will not affect the measurement. To measure the relative distance
between two points in a cable, do the following:
1) Move the active cursor to the beginning of the section to be measured.
2) Press the CURSOR button to switch cursors.
3) Move the newly active cursor to the end of the section to be measured.
40 Mohr CT100 / CT100HF Operator's Manual
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