35
50 Ohm coax with series resistive fault – figure 3-13. Cursor 2 (left cursor) marks
the fault, a step up in impedance that never lets the trace return to normal and
stays added to the total impedance and loop resistance. RG-174 is a small
diameter coax with a high loop resistance due to the thin center conductor, hence
the more dramatic dribble-up in the trace. Cursor2 (right cursor) marks the open
end of the cable. The total length is the distance to C Cursor
∆
(distance
between Cursor 1 and 2) or 99 feet 2 inches (30.2m).
Figure 3-13
Wet 75 Ohm hard-line coax – figure 3-14. Looking at the trace starting at the left
is the test lead connection using F-to-alligator clips leads to bare coax, hence the
up bump in impedance at about 2ft (60cm). Moving right Cursor 2 is next at 12ft 6
inches (3.8m) marking a relatively dry section of the cable. Finally, Cursor 1 at
17ft 1 inch (5.2m) beyond Cursor 2 marking the open end of the cable. The dips
and noise are the result of wet sections so none of the distances can be trusted.
The cable is actually longer than the 29ft 7 inches (9m) indicated by the cursors
total.
Figure 3-14