61
Figure 3-53
Figure 3-54 is an example Measurement Screen with 10ft (3m) of Start
Distance (off-set). Note the Range Scale at the bottom of the trace is now set
for 10 to 60ft (3-18.3m). The upward spike in the trace indicates the open end
of the cable. The first 10ft (3m) of cable and any test lead are not in the trace,
but the cursor reads the cable’s correct length of 58ft (17.7m). Using the Start
Distance off-set by 10ft (3m) permits a better resolution view on the 50ft
(20m) Range than moving up to the 100ft (50m) Range.
Figure 3-54
CAUTION: This feature will set an intentional blind zone between the TDR’s
connector and the start of the trace. Be sure to check the first section of
cable from the TDR’s connector to the planned Start Distance before setting
an off-set and to reset the Start Distance to zero when its use is completed.
Test Lead Null
This feature is designed to measure any test lead in time-delay to end of the
lead and remove the lead from the cable’s measured distance. By measuring
the lead in time-delay rather than distance it eliminates the VF. This way if
the VF of the test lead is different than that of the cable being tested there will
be no affect on the cable’s distance measurement.